Sandy Cairncross and Vivian Valdmanis.
- Isaac CH Fung2 and
Water supply in the context of this chapter includes the
supply of water for domestic purposes, excluding provision for irrigation or
livestock. Sanitation is used here in the narrow sense of excreta
disposal, excluding other environmental health interventions such as solid
waste management and surface water drainage.
The effect of these other measures on disease burden is largely confined
to urban areas and is considerably less than that of water supply, sanitation,
and hygiene promotion (Cairncross and others
2003). More fundamentally, expenditure on solid waste disposal and drainage
is rarely seen as forming part of a portfolio of investments in public health
or competing with public health investments. Rather, it is generally perceived
by decision makers as comparable with other investments in municipal
infrastructure and services, such as roads or public transportation, which are
not considered to be public health interventions.
This chapter focuses on water supply, excreta disposal, and hygiene
promotion and considers the costs and benefits of each in turn. Water supply
and sanitation can be provided at various levels of service, and those levels
have implications for benefits. Water supply and sanitation offer many benefits
in addition to improved health, and those benefits are considered in detail
because they have important implications for the share of the cost that is
attributable to the health sector. From the point of view of their effect on
burden of disease, the main health benefit of water supply, sanitation, and
hygiene is a reduction in diarrheal disease, although the effects on other
diseases are substantial. In the concluding sections, the percentage reductions
arrived at in the discussion throughout the chapter are used together with data
on existing levels of coverage to derive estimates of the potential effects of
water supply and excreta disposal on the burden of disease, globally and by
region, and with cost data to derive cost-effectiveness estimates.
Water Supply
What constitutes a perfectly satisfactory water supply to some consumers
leaves others, even in developing countries, considering themselves unserved.
In much of rural Africa, a hand pump 500 meters from the household is a luxury,
but most residents in urban Latin America would not consider themselves served
by a water supply unless they had a house connection. In Asia, urban planners
would consider a community served if there were sufficient standposts on the
street corner; however, if the water only flows for a few hours per week,
producing lengthy nighttime queues, the residents may regard this situation as
a lack of service and opt to buy water expensively from itinerant vendors. As
these examples illustrate, water supply is not a single, well-defined
intervention, such as immunization, but can be provided at various levels of
service with varying benefits and differing costs.
Levels of Service and Their
Costs
Many public health workers unfamiliar with the water sector assume that
the most important characteristic of a water supply is its improved quality.
However, most of the benefit is attributable to improved convenience of access
to water in quantity. Moreover, global statistics are not available on
the coverage and costs of provision of water in terms of its quality. The Global
Water Supply and Sanitation Assessment 2000 Report (WHO and UNICEF 2000),
the most recent compilation of global statistics on water supply, changed the
way that such data are compiled, from the previous unreliable estimates by
provider agencies to consumers' responses in population-based surveys. The
change required a departure from the old definition of reasonable access to
safe water, because most consumers cannot tell whether their water supply
is safe. They can, however, state the type of technology involved, and that fact
was used to define a new indicator of improved water supply. In the
main, improved water supplies could be expected to provide water of better
quality and with greater convenience than traditional not improved
sources. The report treated the following technologies as improved: household
connection, public standpipe, borehole, protected (lined) dug well, protected
spring, and rainwater collection. Unprotected wells and springs, vendors, and
tanker-trucks were considered unimproved. Bottled water was also considered
unimproved because of concerns about the quantity of water supplied, not
because of concerns over the water quality.
Reasonable access was defined as the
availability of at least 20 liters per capita per day from a source within 1
kilometer of the user's dwelling. Within the broad category of those with
reasonable access to an improved water supply, two significantly different
levels of service can be distinguished:
- house connections
- public or community sources.
In most settings, these subcategories correspond to very different
levels of water consumption, different amounts of time spent collecting water,
and as discussed in later sections, different health benefits.
The Global Water Supply and Sanitation Assessment 2000 Report
also gives median construction costs per person served for the various
technologies in the three main regions of the developing world. These costs are
shown in figure 41.1. However, local conditions, such as the size of
the community to be served and the presence of suitable aquifers, can cause
tremendous variations in the unit cost of water supply.
Median Construction Cost of Water Supply Facilities for Africa, Asia,
and Latin America and the Caribbean
For a community of given size, there are no significant returns to scale
in the number of house connections made. Most of the investment in major works
must be made before house connections can be offered, so that the marginal cost
of each connection is only a fraction of the total. For those and other
reasons, water supply is a natural monopoly requiring "lumpy"
investments, which makes the unit costs difficult to calculate.
The cost of house connections may be representative in Latin America and
the Caribbean, where they are often provided in rural areas. In Asia and
Africa, however, the reported costs of house connections relate almost
exclusively to urban areas because such connections are only rarely provided in
smaller communities. The smaller size of rural communities means that piped
systems in general—and house connections in particular—will tend to be more
expensive per capita there than in urban areas. An overall unit cost figure of
US$150, just above the highest of the three continental medians, is therefore
taken for house connections in the cost-effectiveness calculations.
For public water points corresponding to improved water supply, hydrogeological
and other constraints mean that the cheapest technology is not feasible in
every community. A cost figure of US$40 per capita is about the middle of the
range offered by different technologies (standpost, borehole, and dug well)
providing this level of service for each continent (figure 41.1) and, therefore, seems reasonable for this level
of service, although it can be expected to vary between US$15 and US$65 or
more, depending on local conditions. The range of costs reported by individual
countries for the Global Water Supply and Sanitation Assessment 2000 Report
varied by more than an order of magnitude.
In calculating the cost-effectiveness of investment in water supplies,
one must amortize these capital costs over an appropriate lifetime. Most major
components of an urban water supply system have a potential lifetime of 50
years or more, but a prudent utility would aim to amortize them within about 20
years. A reasonable basis for calculation, for both urban and rural supplies,
is to allow an amount of 5 percent of the capital cost as an annual
straight-line amortization of the construction cost of the water supply.
Construction costs do not represent the full cost of water supplies. The
Global Water Supply and Sanitation Assessment 2000 Report also gives
median reported production costs per cubic meter for urban (house connection)
water supplies as US$0.20 for Asia and US$0.30 for Africa and Latin America and
the Caribbean. If we assume a mean daily water consumption of 100 liters per
capita by those with household connections, those figures give annual per
capita operation and maintenance costs of US$7.30 and US$10.95, respectively,
or 8 to 10 percent of the capital cost of construction. In this chapter, a
generic figure of US$10 is used for the annual per capita operation and
maintenance cost.
Reliable figures for the annual maintenance costs for rural water
supplies are harder to find, particularly because much of the maintenance is
carried out by the volunteer labor of villagers. Arlosoroff and others
(1987), after reviewing a wide range of rural water supply projects in various
countries, concluded that with a centralized maintenance system, the annual per
capita cost of maintenance of a hand pump–based supply can range from US$0.50
to US$2.00, while well-planned, community-level maintenance can bring that
figure down as low as US$0.05 per capita per year. A nominal annual figure of
US$1.00 per capita is therefore used in this chapter. A similar figure can be
applied to urban public standposts, for which volunteer labor is less
forthcoming but transport costs are lower. This maintenance cost represents 2.5
percent of the construction cost arrived at above.
The Time-Saving Benefit
Benefits to health are not normally foremost in the minds of those
provided with new water supplies. An exhaustive study of the economics of rural
water supply by the World Bank concluded that "the most obvious benefit is
that water is made available closer to where rural households need it. . . . It
is not clear that rural populations think much about the relationship between
water and health" (Churchill and others
1987, 21–22).
The Value of Time
The saving in time and drudgery of carrying water home from the source
is substantial, and several reasons exist to attribute a money value to it. The
most powerful argument for the money value of poor women's time is that
households often pay others to deliver their water, or pay to collect from
nearby rather than from more distant sources that are free of charge. Thompson and others
(2001) found that, of urban East African households lacking a piped supply,
the proportion paying for water had increased from 53 percent to 80 percent
over 30 years. In a survey of 12 sites in 10 countries, Zaroff and Okun (1984)
found that households were spending a median of over 20 percent of their income
on the purchase of water from vendors. The prices charged by vendors are
typically more than 10 times—and can be up to 50 times—the normal tariff
charged by the formal water supply utility.
Cairncross
and Kinnear (1992) found that vendor prices increased with the time
required to collect the water, showing that households pay more as the
alternative of collecting water themselves becomes more burdensome. If the
amount paid to the vendor for bringing the water is divided by the time saved
from collecting it, the implicit value that people ascribe to their time can be
calculated. Whittington,
Mu, and Roche (1990), working in rural Kenya, showed in this way that the
implicit value of the time saved was roughly US$0.38 per hour, very close to
the average imputed wage rate for such households of US$0.35 per hour.
Because the poorest urban households typically spend more than 90
percent of their household budget on food, the money they spend on water is
sacrificed from their food budget (Cairncross and Kinnear
1992). The provision of water more cheaply thus offers a substantial
nutritional benefit to the poorest.
Assessing the Time Saved
The cost of water collection in rural areas is usually in time and
effort rather than in money paid to vendors. The saving in time and drudgery
underlies many social benefits. Given the relevance of the time-saving benefit
to water supply policy and the fact that the benefit is usually uppermost in
the mind of the consumer, it is remarkable how few data have been collected on
the amounts of time spent collecting water.
Working in 334 study sites in Kenya, Tanzania, and Uganda, Thompson and others
(2001) found a mean distance from rural unpiped households to their water
sources of 622 meters. In urban areas, the distance was only 204 meters, but
queuing at the tap meant that a water collection journey took almost as long.
Feachem and
others (1978) found in 10 villages of the densely populated lowlands of
Lesotho that the installation of a water supply had saved the average adult
woman 30 minutes per day. In one-third of the villages, the saving per woman
was more than an hour a day. Lesotho has many springs, so that time saving is
likely to be on the low side compared with Africa as a whole.
These time-saving benefits are confirmed by the Multi-Indicator Cluster
Surveys of the United Nations Children's Fund (UNICEF). A recent analysis of
the responses in 23 African countries has produced a more representative
account of water collection journey times in that continent (G. Keast, UNICEF,
personal communication 2003). Nearly half the households interviewed (44
percent) required a journey of more than 30 minutes to collect water, implying
that the women in such households spent an hour or more each day in water
collection. At almost any reasonable level of service, most of that time would
be saved by an improved water supply.
In Asia, an Indian national survey for UNICEF found that women spent an
average of 2.2 hours per day collecting water from rural wells (Mukherjee 1990). A
study in Sri Lanka, which is generally considered to be well provided with
water sources, found that 10 percent of women had to travel more than 1
kilometer to their nearest source (Mertens and others
1990).
Valuation of the Time-Saving
Benefit
Putting a precise figure on the money value of the time of poor people
is a tricky task, even for the most self-confident economist. In 1987,
Churchill and others took US$0.125 per hour as an illustrative but not
unrealistic figure. To take the same figure today could hardly be described as
extravagant. Assuming this valuation of an hour of time—and that a water supply
bestows a mean saving of only 15 minutes per person per day—yields a
conservative estimate of the value of the time-saving benefit of US$11.40 per
year. The data presented earlier indicate that, at least in Africa, the true
figure is nearer to double that amount, enough to justify the full construction
cost of a dug well or borehole supply in a single year. In Latin America and
the Caribbean, costs are higher, and time savings may be less, but rural
incomes are also higher—and so, therefore, is the value of people's time.
Little doubt exists that, in all three regions of the developing world, the
value of time saved is sufficient on its own to justify both the investment
costs (at any reasonable rate of amortization) and the operation and
maintenance costs of water supplies.
Even in settings where water vending is not common, contingent valuation
surveys have widely demonstrated a willingness to pay for water supplies,
particularly at the level of service of house connections (World Bank Water
Demand Research Team 1993). In general, such measured willingness to pay
has exceeded the cost of providing the supplies, and payment to vendors often
exceeds it by many times.
Policy Implications
Whether the consumers actually pay for the full value of the time-saving
benefit, it is what makes water supplies popular and largely it is what
motivates politicians to invest in them. More than half the total annual investment
in water supply in the developing countries of Africa, Asia, and Latin America
and the Caribbean is from domestic sources (WHO and UNICEF 2000).
Most of the investment is from the public sector. In general, investments in
water supply—whether by the governments of developing countries or by external
support agencies—do not come from health sector budgets and are not compared
with other health interventions when investment decisions are made, even though
health benefits do arise from water supply improvements.
Water supply is thus a health-related intervention that comes without
cost to the budgets of the health sector. Although it undoubtedly offers health
benefits, it has a sufficient economic and political rationale in other social
benefits associated with time saving. The health benefits are a positive
externality to this rationale. However, this fact does not mean that the
authorities responsible for public health should ignore the water sector. The
function of the health sector is one of regulation, advocacy, and provision of
supplementary inputs, as appropriate, to ensure that potential health benefits
of water supply are realized to the optimal extent.
For example, the regulatory role of the health sector in quality
surveillance of drinking water is well known and widely accepted. Substantial
and largely unexploited additional potential is present in this role if quality
is interpreted in the wider sense of quality of service rendered by the
water supply utility, in terms not only of water quality but also of quantity,
continuity, coverage, control of sanitary hazards, and cost. Those other
aspects, as will be argued in the following sections, are no less important for
health.
Where a regulatory role is not available to the health sector or
agencies concerned with public health, advocacy can be no less cost-effective.
For example, connection charges are a major barrier to house connections for
low-income groups. In many cities of the developing world, the individual
connection charge is about a month's basic wage. Advocacy of lower connection
charges, with the amount recovered from the monthly water tariffs, can
therefore help achieve an increase in the number of people who have house
connections and who can benefit from the corresponding health gain at no cost
to the public purse. Finally, the health sector can provide important
complementary services, such as hygiene promotion and promotion of low-cost
sanitation to increase coverage; because of the nature of such services, the
water sector, with its focus on technology, is ill-equipped to offer them.
The unit costs of such regulation and advocacy are minimal. One example
is the case of UNICEF's participation over the past 30 years in India's rural
water supply program. UNICEF's investment has represented no more than 1
percent of the total, but its influence has played a central part in the
evolution of the technical and institutional model of the program that supplies
water to 1 in 10 members of the human race.
An example of the effectiveness of such measures is provided by the
interventions of the Mexican Ministry of Health in June 1991. Fostered by fear
of the devastating effects of cholera, these measures included the chlorination
of water supplied for human consumption and the prohibition of sewage
irrigation of fruit and vegetables. As a result, the incidence of diarrhea in
children under five years of age fell from 4.5 to 2.2 episodes per child-year,
and the corresponding mortality rate fell from 101.6 to 62.9 per 100,000
children (Gutiérrez
and others 1996).
The current rate of annual investment per capita in water supply and
sanitation, including both national investment and external aid funds, is
reportedly US$2.25 in Asia, US$7.53 in Africa, and US$8.87 in Latin America and
the Caribbean (WHO
and UNICEF 2000). One percent of the water sector's investment would,
therefore, be US$0.02 to US$0.10 per capita. If each ministry of health in the
developing world were to invest such a sum in public health advocacy and
regulation related to water supply, the sector's performance, at least where
low-income groups are concerned, could be transformed. It is hard to put a
figure on the health effects of such investment, but the Mexican example
suggests that they would be substantial. For the sake of cost-effectiveness
estimation, such spending is arbitrarily assumed to have the effect of ensuring
improved water supplies for an additional 10 percent of the population to which
it refers.
Direct Health Effects
The full list of water-related infections is large and varied, but most
are only marginally affected by water supply improvements. The first effort to
simplify the relationship between water supplies and health in developing
countries was made by David Bradley (White, Bradley, and
White 1972), who developed a classification of disease transmission routes
in terms of whether they were
- waterborne, in the strict sense in
which the pathogen is ingested in drinking water
- water-washed—that is, favored by
inadequate hygiene conditions and practices and susceptible to control by
improvements in hygiene
- water-based, referring to
transmission by means of an aquatic invertebrate host
- water-related insect vector
routes, involving an insect vector that breeds in or near to water.
Whereas the prevention of waterborne disease transmission requires
improvements in water quality, water-washed transmission is interrupted by
improvements in the availability—and hence the quantity—of water used for
hygiene and the purposes to which it is put. Water supply may affect
water-based transmission (for example, if it reduces the need for people to
enter schistosomiasis-infected water bodies) or water-related insect vectors of
disease (for example, if a more reliable supply averts the need for the
water-storage vessels in which dengue vectors breed), though that will depend
on the precise life cycle of the parasite involved and the preferred breeding
sites and behavior of the vector.
Classification and Burden of
Water-related Diseases
Before Bradley's classification can be applied to diseases (rather than
transmission routes), it requires a small adjustment (Cairncross and Feachem
1993) to allow for the fact that practically all potentially waterborne
infections that are transmitted by the feco-oral route can potentially be
transmitted by other means (contamination of fingers, food, fomites, field
crops, other fluids, flies, and so on) all of which are water-washed routes. In
addition to the feco-oral infections, a number of infections of the skin and
eyes can be considered water washed but not waterborne. The final
classification is shown in table 41.1.
The Bradley Classification of Water-related Infections.
The classification can now be used to assess how the disease burden
prevented by water supply is distributed among disease groups. Bradley himself
did this, a time long before the disability-adjusted life year (DALY) had been
invented as a unit of benefit measurement (White, Bradley, and
White 1972, 191). He used official statistics on the number of cases of
each disease diagnosed and treated by health services in East Africa and
combined them with notional percentages by which morbidity and mortality caused
by each condition could be expected to fall if water supply were
"excellent."
Those notional reductions were based on subjective assessments of the
literature available at the time and were described by their author as
"little more than guesses," but it is hard to prove many of them
seriously at fault, even today. A selection is presented in table 41.2.
Percentage Reductions in Disease Rates Assumed by Bradley.
The result of these calculations was that the feco-oral disease group
accounted for 91 percent of the deaths preventable by water supply, 50 percent
of inpatient bed nights, and 33 percent of outpatient consultations. Rosen and Vincent
(2001) have made a similar calculation for the whole of Africa in 1990 and
found that the feco-oral group accounted for 85 percent of the preventable
DALYs. When measured in terms of deaths or DALYs, feco-oral infections account
for the vast majority of the impact, because of the high mortality caused by
diarrheal diseases among young children. Most deaths from diarrheal diseases
are of children younger than age five, and most of those are among children
younger than two. A child death averted is worth 30 DALYs. Varley, Tarvid, and
Chao (1998) have calculated that for diarrhea morbidity reduction to have
the same effect in DALYs as averting one such death, it would have to prevent
115,000 child-days of diarrhea. After the diarrheal diseases, the next most
important category in terms of DALYs (12 percent of the total) is the
water-based group, primarily schistosomiasis. The purely water-washed diseases,
mainly skin infections, represent a more conspicuous portion only when compared
in terms of the burden placed on health services by inpatients or outpatients.
How representative is this African breakdown of the developing world as
a whole? Diarrheal disease among poor communities is cosmopolitan. A global
review of studies of the incidence of diarrhea morbidity could find no clear
geographic or climatic trend (Bern and others 1992),
so the burden of disease is no doubt similar around the developing world. The
second most important disease group is represented by schistosomiasis, which is
absent from much of Asia and Latin America. The relative importance of
feco-oral disease is, therefore, likely to be still greater in the poor
communities of Asia and the Western Hemisphere than it is in Africa.
Epidemiological Questions and
Problems
The predominant contribution of feco-oral diseases to the burden of
disease attributable to water supply raises an important question, because this
group can be transmitted by both waterborne and water-washed routes. It is
important for the water engineer to know whether scarce funding should be spent
on improved water treatment and measures to protect water quality or instead on
providing a limitless supply of water at a high level of access and convenience
and encouraging its use for improved hygiene practices. We need to know, that
is, whether the feco-oral infections endemic in poor communities are mainly
waterborne or mainly water washed.
Moreover, the fact that some diarrheal diseases are still prevalent in
communities with a high level of water supply service indicates that water
supply alone cannot completely prevent these diseases. A further question then,
is this: by how much do water supply improvements reduce diarrheal diseases?
Numerous studies have sought to answer these questions, but they are
hard to answer rigorously, for several reasons. First, it is almost impossible,
ethically and politically, to randomize the intervention. Where the
intervention is an improvement in the level of access to water, it cannot be
blinded; no placebo exists for a standpost. Where quasi-experimental studies
have been used—opportunistically exploiting an intervention allocated by
political or technical means—significant confounding has frequently been found
(Briscoe, Feachem,
and Rahaman 1985).
Confounding has been especially intractable in studies in which the
allocation of facilities has been on a household basis, so that the exposure
groups are self-selected—for instance, studies in which individual households
that have chosen to install a private tap are compared with others that have
chosen not to do so. The former households are likely to be wealthier, better
educated, and more conscious of hygiene than their neighbors, so it would not be
surprising if they were also more likely do many other things that protect
their families from feco-oral disease. The more sophisticated studies have used
multivariate models to control for confounding, but where relative risks are
low and the exposure groups are self-selected, even those models do not
guarantee that confounding is eliminated (Cairncross 1990).
A further difficulty arises from the fact that cases of feco-oral
disease in a given community cannot be considered independent events, because
such diseases are infectious. The sample size, it can be argued, is the number
of such villages rather than the number of individuals enrolled in the study.
Yet a number of important studies in the literature compare a single
intervention area with only one control area.
Other epidemiological weaknesses exist in the data. Blum and Feachem
(1983) reviewed 50 studies of the health effect of water supply and
sanitation projects and noted that every one contained one or more of these
basic errors of methodology. A further weakness in the evidence for the effect
of water supply on diarrheal disease burden is that most of it relates to
diarrheal disease morbidity, and significant assumptions are needed to
extrapolate such evidence to an effect on diarrheal mortality.
Effect on Diarrheal Disease
Esrey and
Habicht (1985) and Esrey and others
(1991) reviewed the same literature from a different perspective. Though
conscious of the methodological shortcomings of most studies, they sought to
assess the overall reductions in diarrheal disease that water supply could be
expected to cause. They applied a number of criteria of epidemiological rigor
and took the median reduction in morbidity reported from each type of
intervention. Their conclusions are summarized in table 41.3.
Median Reductions in Diarrhea Morbidity Reported from Different Water
Supply and Sanitation Interventions.
For more than a decade, this review has remained the most authoritative
on the subject. However, the small reductions in disease that it reports for
water supply conceal an important heterogeneity. Though these overall results
are frequently quoted, the following remark by Esrey and others (1991,
613) has usually been overlooked:
In the studies reporting a health benefit, the water supply was piped
into or near the home, whereas in those studies reporting no benefit, the improved
water supplies were protected wells, tubewells, and standpipes.
In the studies in the two reviews by Esrey and Habicht
(1985) and Esrey
and others (1991) in which the water supply was provided in the home, the
median reduction in diarrheal disease is 49 percent (from 12 studies), and the
reduction from the two better studies is 63 percent. Those reductions are
several times greater than the overall median impacts in table 41.3. The 63 percent figure will be used in the burden
of disease calculations that follow. In the two better studies, the members of
the comparison group were using not an unimproved water supply, but a protected
water source away from the home. The reductions they found are, therefore, in
addition to those resulting from a public standpost level of service.
Some subsequent studies have confirmed this pattern. For example, Bukenya and Nwokolo
(1991) showed in Papua New Guinea that use of a household tap was
associated with 56 percent less diarrhea than use of public standposts
providing water of good quality.
Conditions for Health Effect
Providing a public water point appears to have little effect on health,
even where the water provided is of good quality and replaces a traditional
source that was heavily contaminated with fecal material. By contrast, moving
the same tap from the street corner to the yard produces a substantial
reduction in diarrheal morbidity. How is this pattern to be understood?
The first step to an explanation is an understanding that most endemic
diarrheal disease is transmitted by water-washed routes and is not waterborne.
Although waterborne epidemics of diarrheal diseases such as cholera and typhoid
have been notorious in the history of public health, the endemic pattern of
transmission seems to be different, particularly in poor communities. Five
types of evidence support this view:
- Negative health impact studies. As
mentioned earlier, Esrey and Habicht
(1985) and Esrey
and others (1991) cite a number of studies of the health impact of
water supplies in which water quality improvements have failed to have a
significant effect on diarrheal disease incidence.
- Food microbiology. Studies of the
microbiology of foods in developing countries—particularly the weaning
foods fed to children in the age group most susceptible to diarrheal
disease—have shown such food to be far more heavily contaminated with
fecal bacteria than is drinking water (Lanata 2003),
even when the water has been stored in open pots.
- Seasonality of diarrhea. In countries with a
seasonal variation in temperature, bacterial diarrheas peak in the warmer
season, whereas viral diarrheas peak in the winter. This pattern suggests
that the bacterial pathogens show environmental regrowth at some stage in
their transmission route, which means that they must have a nutritional
substrate. Water is, thus, a less likely vehicle than food.
- Fly-control studies. Trials in rural Asia and
Africa have shown that fly control can reduce diarrheal disease incidence
by 23 percent (Chavasse
and others 1999).
- Hand-washing studies. A recent systematic review
of the effect of hand washing with soap has shown that this simple measure
is associated with a reduction of 43 percent in diarrheal disease and 48
percent in diarrheas with the more life-threatening etiologies (Curtis and
Cairncross 2003).
Those five types of evidence suggest that domestic hygiene—particularly
food and hand hygiene—is the principal determinant of endemic diarrheal disease
rates and not drinking water quality.
The second step is an understanding of how the level of service and
convenience of a water supply influence such hygiene practices in the home.
Taking the amount of water used per capita as an indicator of hygiene changes,
other things being equal, one finds that providing a source of water closer to
the home—and therefore more convenient to use—has very little effect on water
consumption unless the old source was more than 1 kilometer (30 minutes'
roundtrip journey) away from the user's dwelling (Feachem and others
1978).
However, water consumption doubles or triples when house connections are
provided (White,
Bradley, and White 1972), and reason exists to believe that much of the
additional consumption is used for hygiene purposes. For example, Curtis and others
(1995) found that provision of a yard tap nearly doubled the odds of a
mother washing her hands after cleaning her child's anus and more than doubled
the odds that she would wash any fecally soiled linen immediately.
In conclusion, water supplies are likely to have an effect on diarrheal
disease when they lead to hygiene behavior change—that is, when the old source
of water was more than 30 minutes' roundtrip away or when house connections are
provided.
By a happy coincidence, then, the health benefits of water supply are
most likely to be realized in exactly those cases in which the time-saving
benefit is greatest—when the old source of water is farthest away, and when the
new one is on the plot of the individual household. Though water supplies
offering house connections are more expensive, the additional time savings
offered by this level of service mean that people are willing to pay more for
them. Moreover, collecting revenue from households with private connections is
far simpler than collecting it from public taps because the sanction of
disconnection can be used against households that default on payment of the
tariff.
Calculating the burden of disease associated with inadequate water
supply requires a figure for the reduction associated with the levels of service
for which coverage statistics are available. The following burden of disease
calculations are based on a reduction of 17 percent from an improved public
water supply (table 41.3) and of a further 63 percent from house
connections.
The effect of water supply improvements (and of hygiene practices such
as hand washing) on diarrhea mortality can be expected to be at least as great
as—and probably greater than—their effect on morbidity for several reasons. A
theoretical argument for this improvement pattern is given by Esrey, Feachem, and
Hughes (1985) in terms of infectious doses. Esrey and others
(1991) also reported a median reduction of 65 percent in diarrhea mortality
attributable to water supply, sanitation, or both in three studies, compared
with 22 percent from 49 studies of morbidity. The effect of hand washing on
life-threatening diarrheas—shigellosis, typhoid, cholera, and hospitalized
cases—is greater than that on diarrhea morbidity as a whole (Curtis and Cairncross
2003). Finally, the two known direct studies in the literature of the
effect of house connections on diarrhea mortality ("Serviço Especial da
Saúde Pública," an unpublished study in Palmares, Pernambuco, Brazil,
cited by Wagner and
Lanoix 1959; Victora
and others 1988) found reductions of 65 percent (relative to a public
standpost) and 80 percent (relative to various communal sources, some
polluted), respectively.
Effect on Other Disease
Categories
Water supplies have a beneficial effect on a number of disease groups
other than diarrhea, although the corresponding burden of disease is far less.
The median reductions in morbidity from other water-related conditions,
reported by Esrey
and others (1990), are shown in table 41.4.
Median Reductions in Morbidity Associated with Improved Water Supply and
Sanitation: Conditions Other Than Diarrhea, Related Most Closely to Water
Supply.
To be effective in controlling schistosomiasis, the water supply must be
so convenient as to discourage water contact for laundry and bathing. It is
unlikely that this level of convenience can be achieved without house
connections.
Evidence suggests that water availability and hygiene can produce
substantial reductions in trachoma (Emerson and others
2000). Because the reductions come from hygiene improvements such as hand
and face washing, they are also likely to be greatest with house connections.
Dracunculiasis is affected by water quality, but the simplest improved water
supply is adequate to prevent transmission.
Conflicting evidence exists about whether water supply or improved
water-washed hygiene affects the transmission of intestinal helminths. On one
hand, Henry (1981)
found in an intervention study in St. Lucia that piped water supplies were
associated with a 30 percent reduction in ascariasis among children under age
three over a two-year period. On the other hand, Han and others (1988)
showed in Burma that an intervention to promote hand washing with soap had no
effect on prevalence or intensity of infection with Ascaris spp.
However, the potential contribution of water supply to reducing the burden of
disease through its effect on these other infections is relatively minor when
compared with its effect on diarrheal disease.
Excreta Disposal
In much the same way as with water supply, care is needed to ensure that
different people who talk about sanitation are referring to the same thing.
When the WHO-UNICEF Joint Monitoring Program was compiling the Global Water
Supply and Sanitation Assessment 2000 Report (WHO and UNICEF 2000),
a major effort was needed to persuade some of the Latin American partners that
a pit latrine, considered a status symbol in much of rural Africa, was an
acceptable form of excreta disposal. In some countries, even engineered
sewerage systems are considered unacceptable if not connected to a functioning
wastewater treatment plant.
Levels of Service,
Technologies, and Their Costs
A wide range of technologies is used, particularly for settings in which
low-cost solutions are required, and this variation has led some to inquire
whether the different types of latrine might confer differing health benefits.
In the early 1980s, the World Bank established a Technology Advisory Group for
low-cost sanitation, and this question was among those it was asked to
investigate. Using field studies and a thorough literature review, the group
concluded that all types of systems can be operated hygienically, and that
The greatest determinants of the efficacy of alternative facilities are,
first, whether they are used by everyone all the time, and second, whether they
are adequately maintained. . . . Pit latrines would, from the viewpoint of
health rather than convenience, approximate the same rating as a waterborne
sewerage system. (Feachem
and others 1983, 49–50)
The group therefore judged it most appropriate not to distinguish
between sanitation technologies and to consider all of them as providing
adequate access to sanitation as long as they were private or shared (but not
public) and hygienically separated human excreta from human contact. This
definition was followed in the Global Water Supply and Sanitation Assessment
2000 Report, which accepted only sewerage, septic tanks with soakaways,
pour-flush latrines, and pit latrines as improved technologies. Service or
bucket latrines and latrines with an open pit were not accepted. The effect of
technology type on health benefit is discussed further in the sections that
follow.
Public latrines, however, do not provide an adequate solution to the
excreta disposal needs of a community. Quite apart from the notorious and
widespread inadequacies in their maintenance, they are not usually accessible
at night or by the elderly, by those with disabilities, or—if there is an entry
charge—by young children. Thus, some promiscuous defecation continues to be
practiced, particularly by children, in communities where public latrines are
the only level of service available.
Figure 41.2 shows the regional median construction costs per
capita of the various sanitation technologies found by the Global Water
Supply and Sanitation Assessment 2000 Report. Although the simple, on-site
systems tend to be cheaper than systems such as sewerage and septic tanks, the
difference is less than might be expected. For example, a World Bank survey in
several developing countries found the mean cost of conventional sewerage to be
10 times that for on-site systems such as improved pit latrines and pour-flush
toilets (Kalbermatten,
Julius, and Gunnerson 1982). It is likely that the off-site costs of
sewered systems and the cost of the additional water needed for them to
function have not been fully included in national reports to the Global
Water Supply and Sanitation Assessment 2000 Report. For the purposes of
calculating cost-effectiveness, a construction cost of US$60 per capita seems
adequate for basic sanitation facilities (a household pit latrine,
ventilation-improved latrine, or a pour-flush toilet) in any region of the
developing world. Taking a relatively short lifetime of five years for a
latrine and straight-line amortization gives an annual cost of US$12 per capita
per year. In such a short lifetime, very little maintenance is normally
required, other than occasional cleaning; the cost of maintenance is,
therefore, considered to be included in the amortized annual cost.
Median Construction Cost of Sanitation Technologies in Africa, Asia, and
Latin America and the Caribbean
That said, it should be borne in mind that substantially cheaper
solutions are often feasible, such as the "15 taka latrine" (costing
only US$0.27 per household) developed in Bangladesh, which includes a
pour-flush pan made of tin sheet and an odor-and insect-proof seal made of
flexible plastic pipe.
Social Benefits
Like water supply, sanitation offers a number of social benefits in
addition to direct health gains, which tend to feature more prominently in the
minds of the users. This outcome is illustrated by the responses given by a
sample of householders in rural Benin when asked to rate the importance they
ascribed to the various benefits of latrines on a scale of 1 to 4 (table 41.5). Health-related benefits (shown bold in table 41.5) were rarely mentioned spontaneously and generally
rated among the less important benefits.
Benefits of Latrine Ownership as Perceived by 320 Households in Rural
Benin.
With sanitation as with water supply, strong gender differences exist in
the perception of the social benefits of sanitation. For male heads of
household in Benin as in other countries around the world, enhanced social
status figures highly among the benefits of latrine ownership, whereas for
women, security, convenience, and aesthetic factors count for more. Women who
lack sanitation often risk sexual harassment on the way to and from their
defecation site. In some cultural settings, women are constrained to go out for
defecation and urination only during the hours of darkness, effectively
becoming prisoners of daylight. Though no systematic study has been made of the
health implications of such practices, they are likely to include an increased
prevalence of urinary tract infections. The emancipation that a latrine bestows
on such women cannot lightly be dismissed.
Willingness to Pay
The governments of developing countries cannot afford to provide heavily
subsidized sanitation to all—or even to the majority—of their populations. The
2.6 billion people in Africa, Asia, and Latin America who do have adequate
sanitation—53 percent of the population of those regions—have paid most of the
cost themselves. Even those of the urban poor who do not have sanitation have
expressed a willingness to pay for its full cost—or at least the local cost
(excluding major interceptor sewers and treatment works, if required)—in a
number of surveys, as long as credit is available on reasonable terms to smooth
the cash flow (Altaf
1994). With regard to the rural poor, the success of well-conceived sanitation
promotion programs in achieving coverage close to 100 percent, without a
substantial subsidy, in some of the poorest rural communities in the world (Allan 2003) shows
that people are willing to pay for sanitation if a suitable product is offered
to them on suitable terms.
Why then do 2.4 billion people still lack sanitation? Several factors
constrain the expression of the existing demand.
The constraint most frequently mentioned by unserved householders is
cost, but this factor is usually more a perceived constraint than an objective
one, for several reasons. First, many households are unaware of the true cost
of latrines in their area, or the lower-cost models are not offered because
local suppliers and artisans do not know about them or are attracted by the
greater margins to be made on the more expensive technologies. Second, the high
cost of capital to the poor rules out their borrowing the cost of a latrine,
which to them would be a substantial investment. Third, they may be wary of
investing in a property that belongs to their landlord, lest it be used as an
excuse for a rent increase or even eviction. They may also feel, with some
reason, that it is for the landlord to make the investment, rather than
themselves, and they may be waiting for the landlord to do so. This belief has
a similar effect to the common misapprehension of citizens, often encouraged by
politicians, that the local government is responsible for sanitation and will
eventually come to their aid; in either case, the outcome is inaction.
Other constraints include lack of ready access to necessary techniques
and skills or to specific building materials and components. Where the skills
exist locally, residents may lack confidence in the quality of work and value
for money offered by the local artisans, or they may not know how to contact
the right artisans. In many urban areas, local building regulations make
low-cost sanitation technologies illegal.
Those constraints are compounded by the fragmentation of governmental
responsibility for sanitation. Often it is devolved to local governments with
little capacity to implement sanitation improvements. At the national level,
one ministry may be responsible for sewerage and another for low-cost
technologies; one may be responsible for construction, another for promotion,
and a third for enforcing building codes and planning regulations.
Policy Implications
There are important externalities to households' investment in sanitation.
Households are protected from their own feces by their sanitation facilities,
but so, too, are their neighbors, and this factor is probably more important in
epidemiological terms. If households are not fully aware of the health
benefit—or if much of it accrues to others—a case exists for public
intervention to increase coverage because these externalities exist.
This public intervention need not be in the form of subsidy. Strong
arguments can be marshaled against a subsidy for low-cost sanitation (Cairncross 2003a).
Subsidy limits the number of facilities that are built to the size of the
subsidy budget; it encourages the design and marketing of unaffordable
sanitation systems; it frequently leads to capture by the better-off, who
install expensive toilets while the poor go without; and it distorts the
market, diverting the efforts of latrine builders who would otherwise be
seeking to meet the needs of low-income groups.
The intervention can be by regulation. National and local governments
have substantial regulatory powers that can be used to increase sanitation
coverage without significantly increasing costs or public expenditure. For
example, more than 90 percent of households in the town of Bobo Dioulasso,
Burkina Faso, have their own latrine (Traoré and others 1994)
as a direct result of the local administration's practice in the past of
withdrawing rights of land tenure from owners who did not build a latrine on
their plot within a specified time. Another regulatory intervention is to
enforce the obligation of landlords to provide sanitation for their tenants.
An alternative strategy is to provide support to the marketing of
sanitation. This strategy can be undertaken in a number of ways that are not
feasible for the existing producers, mainly artisan builders and small
component manufacturing workshops. Those interventions would aim principally at
overcoming the constraints to the expression of effective demand for sanitation
and could include the following:
- advertising and other forms of promotion
- facilitation of building regulation approval
- brokerage to put potential purchasers in touch with providers
- quality assurance and guarantee schemes
- training in low-cost construction techniques and in marketing
- centralized production of essential components
- provision of pit emptying and desludging services.
Promotion of improved hygiene practices, including appropriate use and
maintenance of the sanitation facilities, is another possible intervention by
the public sector. All of those measures will help increase sanitation coverage
and health benefits and are appropriate interventions for the health sector.
The costs of several of them are recoverable (after an initial launch period)
as fees, so that public intervention need not require public expenditure.
Costs of Promotion
The costs of promotion and administration found in two government-run
rural sanitation programs documented by the World Bank were US$16.80 (Zimbabwe)
and $20.00 (the Philippines) per latrine, respectively (Cairncross 1992).
Because these costs are largely fixed, the cost per unit falls as the number of
units built increases. Unit costs will therefore be high in relatively
unsuccessful programs. Successful programs, on the other hand, often engender
the construction of more latrines than they can account for, which also gives an
upward bias to the promotional costs per unit built. For example, for every
latrine built by Lesotho's rural sanitation program in the late 1980s, four
others were built independently but as a result of its promotional activities.
More recently, successful sanitation programs managed by nongovernmental
organizations (NGOs) have documented slightly lower unit costs for promotion.
For example, the Zimbabwean NGO AHEAD (Applied Health Education and Development),
working through district-level health staff and a network of community health
clubs, achieved the construction of 3,400 latrines in Makoni district within
two years at a total promotional cost of US$45,660, or US$13.43 per unit,
equivalent to US$2.24 per household member served (Waterkeyn 2003).
In Bangladesh, WaterAid and its partner, a local NGO named VERC (Village
Education Resource Centre), have developed an approach that has successfully
achieved 100 percent sanitation coverage and the elimination of open defecation
in more than 100 villages in six districts at a cost of US$8 per household, or
US$1.50 per capita (Allan
2003). Both programs also promoted domestic hygiene practices in addition
to the construction and use of latrines. In Bangladesh, all (and in Zimbabwe,
most) of the costs of latrine construction were paid by the population
themselves.
The programs in Bangladesh and Zimbabwe were particularly successful and
well managed. The promotion cost is taken as US$2.50 per capita for
cost-effectiveness calculations, which is slightly above the higher of the two,
to allow for the imperfections of sanitation programs in the real world.
Direct Health Benefits
Evidence supports the claim that improved excreta disposal helps prevent
a number of diseases, including diarrhea, intestinal worm parasites, and
trachoma. Of these, the effect that accounts for the largest burden of DALYs is
that on diarrheal disease.
Diarrheal Disease
The effect of sanitation on diarrhea morbidity has already been
mentioned. Table 41.3 shows the results of Esrey and others'
(1991) review, attributing a median reduction in incidence of 36 percent to
sanitation. Although this figure is the median of the five "better"
studies, it must be interpreted with great care because almost all the known
studies on the health effects of sanitation are observational studies that use
self-selected exposure groups. Confounding by a sense of hygiene is likely to
be a significant problem in any such study. From Brazil to Bangladesh, the
owners of latrines have been observed to behave more hygienically than their
neighbors in practices such as hand washing that are not affected by the
presence of a latrine (Hoque and others 1995—see
table 41.6; Strina and others 2003).
It is thus impossible to prove, except by an intervention study, that any
health benefit associated with latrine ownership is due to the latrine and not
to the hygiene habits of latrine owners.
Factors Associated with Hand-Washing Behavior by 90 Women in Bangladesh.
The overall reduction in diarrhea from sanitation quoted by Esrey and others
(1991) likely disguises considerable heterogeneity in terms of the context
rather than the type of sanitation technology. For example, sanitation is
likely to have a greater effect on diarrheal disease in high-density urban
areas, where open defecation leads to gross fecal pollution of the
neighborhood, and less effect in rural communities, where all but the youngest
children use communal defecation sites some distance away from their homes.
For example, Moraes
and others (2003), working in urban favelas in northeast Brazil,
found that diarrhea incidence among children in households with a toilet was
half that in households that did not have one. This comparison is likely to be
affected by confounding because the households with toilets were a self-selected
group. Comparison between communities is less likely to be affected by
confounding, but Moraes and others found a greater reduction. The mean
incidence of diarrhea in young children in communities with sewers was only
one-third of that in the communities that, for administrative and technical
reasons, did not have sanitary drainage.
Thus, although the quality of the studies reviewed by Esrey and others
(1991) was in general poor and the range of reductions wide, little doubt
exists that excreta disposal can be associated with significant reductions in
diarrhea morbidity. Studies showing that proximity to open or overflowing
sewers (Moraes and
others 2003), failure to dispose hygienically of children's stools (Traoré and others 1994),
or the presence of excreta on the ground in the household compound (Bukenya and Nwokolo
1991) is a risk factor for fecal-oral infections provide supporting
evidence for the likely effect of sanitation infrastructure, particularly in
urban settings, on diarrheal disease transmission.
In conclusion, there are some reasons, such as the likelihood of
confounding, to believe that Esrey and others'
(1991) median reduction is an overestimate, but reasons exist also to
believe that the reductions measured were not as great as they might have been
had the provision of sanitation been accompanied by hygiene promotion to ensure
that the facilities were fully and appropriately used (especially by young
children) and maintained. A systematic review of the effect of sanitation on
diarrheal disease is urgently required. Meanwhile, and on balance, Esrey and
others' median reduction of 36 percent in diarrhea incidence is the most
authoritative estimate available.
Interaction with Water Supply
The results of Esrey and others'
(1991) review suggest that the effect of water supply and sanitation
combined is no greater than that of either on its own. However, that conclusion
is based on only two studies, and the percentage reductions found in the
individual studies of each type of intervention exhibit a wide range.
Reflection on how in practice each of the two interventions interrupts the
transmission of fecal-oral pathogens would suggest that their effects would be
largely independent: whereas water supply helps prevent contamination of
drinking water, hands, and food, excreta disposal helps prevent contamination
of the household yard and surroundings, including children's play areas. Esrey and others
(1990) reported three other studies in which sanitation and water supply
had a greater effect together than individually, but the reductions in diarrhea
incidence in those studies could not be calculated.
For the purpose of burden of disease calculations, therefore, the
effects of water supply and sanitation improvements on diarrhea are considered
here to be independent and additive, which has the advantage of simplicity.
Effect on Other Disease
Categories
The first evidence for the health benefits of excreta disposal related
not to its effect on diarrheal disease but on intestinal helminths.
A prolonged series of in-depth studies from 1920 to 1930 by researchers
of the Rockefeller Foundation established beyond doubt that promiscuous
defecation, especially in the household surroundings and particularly by
children, played a major role in the transmission of Ascaris spp., Trichuris
spp., and hookworms in a range of settings from Panama to China and the
southeastern United States. By implication, the use of sanitary toilets should
interrupt transmission by that route.
However, more recent attempts to measure the reductions in parasite
prevalence or intensity attributable to improved sanitation have often suffered
from the same shortcomings as the studies of their impact on diarrheal disease;
many have been cross-sectional studies and, therefore, subject to confounding.
Esrey and
others (1991), in reviewing this literature, found that water supply and
sanitation reduced the prevalence of ascariasis by a median of 28 percent
(range 0 to 83 percent) and of hookworm infection by 4 percent (0 to 100
percent). Those reductions are likely caused by the sanitation rather than by
the water-supply improvements. Indeed, three of the nine positive studies of
ascariasis and three of the five positive studies of hookworm involved
sanitation alone. It is also likely that the effect of excreta disposal on Trichuris
infection is similar to that on ascariasis (Henry 1981).
Much emphasis has been placed in recent years on chemotherapy as a
control intervention for intestinal helminths, particularly the chemotherapy of
schoolchildren. However, that option is not always sustainable because the
children are quickly reinfected by the eggs and larvae that remain in the
environment. Sanitation, particularly school sanitation, has been adopted by
the major international donor agencies as an integral component of the FRESH
(Focusing Resources on Effective School Health) framework to ensure its
sustainability.
A study in Bangladesh (Mascie-Taylor and
others 1999) suggested that chemotherapy was more cost-effective (though
less effective) as a helminth control intervention than a health education
program that included the promotion of sanitation. However, the health
education program was excessively labor intensive and, therefore, expensive; it
involved the constant deployment of six health educators and a supervisor in each
study area of only 550 households, resulting in a cost of Tk 1600 (US$30) per
household, compared with Tk 330 (US$6) per year for chemotherapy. That cost
compares with the total cost of US$8 per family for WaterAid's successful
"100 percent sanitation" approach in rural Bangladesh (Allan 2003).
Whereas the promotion of sanitation is a one-time cost, the cost of
chemotherapy is a recurrent annual expenditure. Allowing for such a sanitation
promotion initiative once every five years—and using the chemotherapy costing
of Mascie-Taylor
and others (1999)—sanitation promotion is more cost-effective against
helminths in Bangladesh than is chemotherapy. If the cost were apportioned
between the effect on diarrheal disease and the effect on helminths, sanitation
would be far more cost-effective than chemotherapy.
Sanitation can also help prevent trachoma. More than 70 percent of the
incidence of this infection has been shown to be caused by flies, mainly of the
species Musca sorbens, which breeds preferentially in scattered human
feces. Pit latrines have been shown to reduce the population of these flies by
depriving them of their breeding sites (Emerson and others
2004).
Hygiene Promotion
To a greater degree than with water supply and sanitation, lamentably
little reliable evidence exists on the cost or the effectiveness of
interventions to change hygiene behavior and still less on the relative
cost-effectiveness of different approaches to the design of such interventions.
The Shortage of Evidence
With regard to effectiveness, Loevinsohn (1990)
reviewed health education interventions in developing countries and applied
four relatively modest criteria of scientific rigor to the 67 published studies
he found:
- a description of the intervention in sufficient detail to allow its
replication
- an objective outcome measure, based either on health status or on
behavior change
- a control group and a sample size greater than two clusters or 60
individuals
- a description of the target population (in terms of their level of
education and other factors) adequate to permit a judgment of the
relevance of the study to other contexts.
Only three studies were found to meet all four criteria. One (Stanton and Clemens
1987) dealt with environmental hygiene promotion and raises some
doubts—although the hygiene behavior of the intervention group was better than
the control, both were significantly worse than they had been before the
intervention.
A subsequent review of 31 studies (Cave and Curtis 1999)
found 5 more studies that could be considered methodologically sound, but none
showed a clear effect on behavior. Of a further 11 studies of
"reasonable" rigor, only two showed a major effect on behavior.
Shortcomings also exist in the cost data. Many costings are based on
budget forecasts and not on real expenditures. Even when actual expenditures
are used, major difficulties exist in apportioning the overhead costs that make
up a significant proportion of the total. Health educators and the resources
they use (such as vehicles) are rarely dedicated exclusively to health
education. A further problem in the derivation of unit costs is agreeing on the
denominator, which can be the number of people attending health education
sessions, the number of members in their households, or the number of people in
the target catchment area. For those reasons, different analysts are likely to
derive different unit costs from the same data; indeed, the same authors have
on occasion arrived at widely differing unit cost figures from the same data.
Time adds a further dimension to this discussion. Do interventions to
promote hygiene behavior change have to be implemented continuously, or at
least annually, if their effect is to be sustained, or are such changes
self-sustaining?
Sustainability
We will take the last question first. Wilson and Chandler
(1993) returned after two years to a population in which a four-month
intervention to promote hand washing with soap had included provision of free
soap. They found that 79 percent of mothers, the original target group, had
continued the practice despite the fact that they now had to buy the soap.
Further evidence of the sustainability of new hygiene behaviors was
found by Cairncross
and Shordt (2003) in a collaborative study with partner organizations in
six developing countries in Africa and South Asia. Target populations of
previous hygiene promotion projects were visited at 12-month intervals, and
various indicators of hygiene behavior were assessed and compared. In four of
the six countries, indicators for populations in which the intervention had
ended relatively recently were also compared with those in areas where the last
intervention had ended several years previously. Those two types of comparison,
with the various indicators assessed in each country, allowed a total of 46
comparisons to be made. Only in three such comparisons was there any indication
of a falling-off of hygiene with time since the intervention ended; in one
case, the falling-off was attributable to the deteriorating condition of the
latrines from wear and tear rather than to a decline in compliance.
In some cases, new hygiene practices have become stronger or more
prevalent after the ending of external intervention to promote them, as they
become self-propagating and consolidated in the community's material culture (Allan 2003).
It is likely that hygiene promotion activities need to be repeated from
time to time—say, every five years—but are not required on a continuous basis.
It follows from this observation that calculations of cost-effectiveness should
take into account the morbidity and mortality averted not only during the
implementation of the intervention, but also for a number of years—perhaps
five—thereafter.
Costs
Cases in which the costs as well as the effectiveness of hygiene
promotion programs have been documented objectively are few indeed. In the
absence of suitable data, Varley, Tarvid, and
Chao (1998) calculated a costing for a typical program from first
principles, arriving at a cost of US$3 (range US$2 to US$3) per household per
year, or US$0.60 per capita.
One of the few cases in which data exist is a program in urban Burkina
Faso described by Borghi
and others (2002). Their data show that the total cost to the provider of
the three-year intervention was US$0.65 per capita, or US$4.54 per seven-person
household, after deducting the cost of the international research component. Of
this total, 63 percent is composed of administration and undifferentiated
start-up costs of the project. Most of the remaining costs were accounted for
in roughly equal measure by house-to-house visits, discussions in health
centers, hygiene lessons in schools, and street theater presentations.
Additional costs were incurred by the 18.5 percent of households that
complied, practicing improved hygiene as a result of the program, amounting to
US$8 per household per year. More than 90 percent of that sum was the cost of
soap for hand washing.
However, on the basis of the observed increase in prevalence of hand
washing with soap, the intervention was estimated to have averted sufficient
diarrhea morbidity and mortality to save US$2.80 per household per year (US$15
per compliant household per year) in direct costs of medical care and indirect
costs attributable to lost productivity. Of this total, 93 percent represented
the lost future productivity associated with the deaths of young children.
Waterkeyn
(2003) provides an example from rural Zimbabwe. In the two districts in
which the Community Health Clubs approach was examined, it was successful in
increasing the prevalence of hand washing with soap among the club members by 6
percent and 37 percent, respectively, and it was successful in reducing the
prevalence of open defecation by 29 percent and 98 percent, respectively. The
marginal cost of the intervention, which used existing health staff, was
US$4.00 per club member, or an average of US$0.67 per member of an affected
household. Including the salaries of staff members would roughly double the
figure to about US$1.40 per capita.
Those figures can be compared with an estimate of US$5.00 per mother (in
1982 dollars) by Phillips
and others (1987) based on a review of several programs. Assuming that
roughly 1 in 10 members of the population are mothers of young children, this
cost is equivalent to about US$0.50 per capita. For cost-effectiveness
analysis, a nominal cost of US$1.00 per capita is, therefore, taken because it
is roughly the midpoint of the range of recent estimates.
Effect on Diarrhea
Esrey and
others (1991) found only six studies of the effect of hygiene promotion interventions
on diarrhea morbidity, with a median reduction of 33 percent. A subsequent
review by Huttly,
Morriss, and Pisani (1997) arrived at a similar result—a median reduction
of 35 percent.
The interventions promoting the single hygiene practice of washing one's
hands with soap tended to achieve greater reductions in disease than those that
promoted several different behaviors. That finding was confirmed by a
systematic review of the literature on hand washing (Curtis and Cairncross
2003), which concluded that hand washing with soap—and interventions to
promote it—could reduce diarrhea morbidity by 43 percent and life-threatening
diarrhea by 48 percent. Because the effect of diarrhea prevention in DALYs is
mainly attributable to the prevention of diarrhea deaths, the higher of these
two figures is more appropriate for calculating the effect of hygiene promotion
on the burden of disease.
It is not surprising that interventions advocating more behavior changes
should have less effect, because numerous messages dilute one another in the
minds of the target audience. Because some of the interventions in the
systematic review were planned without an adequate prior program of formative
research, it is possible that they could have had a still greater effect if
they were better conceived.
Effect on Respiratory
Infections
Reasons exist to believe that hand washing with soap could be a
cost-effective intervention not only against diarrheal diseases, but also for
the prevention of acute respiratory infections (ARIs). The intervention is
plausible, given what is known about the transmission routes of ARIs,
and there is also epidemiological evidence, in that all six published studies
of the effect of hand washing on ARIs show a significant reduction (Cairncross 2003b).
These two disease groups are the most important causes of child
mortality worldwide, and respiratory infections also cause significant adult
mortality, for which no alternative preventive intervention is yet available,
field-tested, and ready for implementation. A randomized, controlled trial of the
efficacy of hand-washing promotion on an ARI outcome is an urgent priority for
future research.
Interactions with Water Supply
and Sanitation
It can be argued that there is little point in encouraging people to
wash their hands if they do not have access to water or to use a latrine if
they do not have one.
The argument has only limited validity where sanitation is concerned; an
important role for any hygiene promotion is to promote sanitation itself. With
regard to water, in the studies reviewed by Curtis and Cairncross
(2003), the reductions in disease achieved by hand washing in settings with
indoor piped water supply were not significantly different from those achieved
elsewhere. Given that the rationale is ambivalent and the evidence
inconclusive, the simplest plausible assumption is that the effects of water
supply, sanitation, and hygiene promotion on diarrhea are independent and
additive to one another.
Effect on Burden of Disease
The effect of water supply, sanitation, and hygiene on the global burden
of disease can now be estimated, in two stages. First, the evidence presented
in this chapter is used to arrive at the reductions in diarrhea that are
expected to result from the various combinations and levels of service and that
are assumed for the calculation. Then, these figures are applied to the
coverage levels for individual countries and the burden of diarrheal disease
prevailing in the different regions of the world. Because such a calculation
has been done before by Prüss and others
(2002) from rather different premises, it was desirable to examine the
comparability of the results.
Assumptions: Reductions in
Diarrheal Disease
In summary of the discussion of health effects in this chapter, water
supply, sanitation, and hygiene promotion are considered to be associated,
under typical conditions, with the reductions in diarrheal disease morbidity
shown in table 41.7. These reductions are considered to be independent
of one another, so that the relative risks for several interventions can be
multiplied.
Assumed Reductions in Diarrhea Attributable to Water Supply, Sanitation,
and Hygiene Promotion.
These assumptions can be compared as follows with the assumptions
underlying a previous calculation of the global burden of disease from water,
sanitation, and hygiene (Prüss and others 2002;
WHO 2002). For
that calculation, the following seven scenarios were considered:
VI. No improved water supply or basic sanitation
Va. Basic sanitation only
Vb. Improved water supply only
IV. Improved water supply and basic sanitation
III. Improved water supply and basic sanitation plus house connection
water supply, or improved hygiene or water disinfected at point of use
II. "Regulated" water supply (presumably house connection) and
full sanitation
I. Ideal situation, corresponding to absence of disease transmission
through water, sanitation, and hygiene.
Scenario II is essentially the position prevailing in industrial
countries. Leaving out scenarios I and III, which apply to only a small
proportion of the population, the following scenarios are broadly equivalent to
the categories considered earlier in this chapter:
VI. No improved water or sanitation
Va. Sanitation only
Vb. Improved water supply (public source)
IV. Both improved water supply and sanitation
II. House connection water supply, and sanitation.
In the Prüss model, the relative risks associated with transition from
scenarios Va and Vb to VI are taken as 1.26 and 1.60, respectively, comparable
with the figures of 1.20 and 1.56 in table 41.7. However, Prüss and others
(2002) assume equal risks in scenarios IV and Va, whereas a relative risk
of 1.20 follows from the assumption in this chapter that the effects of water
supply and sanitation are independent. The Prüss model assumes a relative risk
of 1.54 between scenarios III and IV, corresponding to the diarrhea reduction of
35 percent from hygiene promotion found by Huttly, Morriss, and
Pisani (1997). Scenario III is essentially a theoretical construct, and
between it and scenario II a further relative risk of 1.8 is assumed (in what
Prüss and others term their realistic approach), on the basis of some
recent trials of home disinfection of water, giving a total of 2.76 between
scenarios IV and II. The latter figure is close to the corresponding value of 2.70
implied by the assumptions made here, for different reasons. Scenario I, like
scenario III, is included not because it is prevalent in reality, but to
illustrate a point. Its equivalent would be the generalized and effective
implementation of a well-conceived hygiene promotion intervention. Because such
hygiene promotion has hardly ever been provided to whole populations, it is
similarly hypothetical. From that perspective, the corresponding relative risks
of 2.5 (Prüss and
others 2002) and 1.92 (table 41.7) are of a similar order of magnitude.
The similarity of the two sets of assumptions, based on rather different
premises, is illustrated in figure 41.3.
Comparison of Assumptions Made by Prüss and others (2002) and in this
chapter
To allow for the uncertainty in their assumptions, Prüss and others
(2002) calculated the burden of disease attributable to water supply,
sanitation, and hygiene using two approaches. The realistic approach
used the assumptions described above and shown in figure 41.3. The minimal approach assumed no
difference in risk between scenarios II and III. Given the ideal and
hypothetical nature of scenario I and the low probability of intensive hygiene
promotion being funded for a population that already benefits from high levels
of water supply and sanitation provision, we consider the model on the right of
figure 41.3 as optimistic and prefer to take for our
more realistic approach the less ambitious baseline of house connections
and full sanitation, which approximates the current position in most of Western
Europe and North America. This approach responds to recent calls for
"baselines and counterfactuals which should include alternative,
operationalizable policy/program options (including the status quo)" (Ezzati 2003, 458).
It also has the advantage of providing an estimate of burden of disease to
which the industrial countries contribute only a negligible amount.
Calculation of Burden of
Disease
Prüss and
others (2002) worked with water and sanitation coverage data for individual
countries (WHO and
UNICEF 2000) to derive distributions of the population in each region
between five of the seven scenarios, as shown in table 41.8. They then combined these figures with the
relative risks in figure 41.3 and diarrhea incidence and case fatality rates
from Murray and
Lopez (1996) to derive estimates of the number of DALYs attributable to
water supply, sanitation, and hygiene in each region and mortality subregion.
The results are shown, for their realistic and minimal models, in the first two
columns of table 41.9. The realistic estimates are those presented in
the World Health Report 2002 (WHO 2002, 225).
Distribution of the Population between Scenarios of Water Supply and
Sanitation Provision (percent).
Distribution of DALYs Attributable to Diarrhea Caused by Poor Water
Supply, Sanitation, and Hygiene by Subregion, According to Various Assumptions (thousands).
Using the same spreadsheets but the relative risks on the right of figure 41.3, we derive the results in the third and fourth
columns of table 41.9 for the optimistic and realistic versions of the
present model. The figures for the burden of disease attributable to deficient
water supply, sanitation, and hygiene in the industrial countries of Europe,
North America, and the Pacific are very different, but the global totals are
remarkably similar.
It should be no surprise to find that the attributable burden in the
industrial (that is, low-mortality) countries of Europe, North America, and the
Pacific is zero or very close to zero. The realistic model was deliberately
designed to take as its baseline the conditions prevailing in those countries.
This finding does not mean that no diarrheal disease in those countries can be
attributed to deficient water supply, sanitation, or hygiene; rather, it means
that the baseline there is the current condition, because no realistic policy
option is available to reduce the burden of such disease in the immediate
future.
Table 41.10 shows the two realistic assessments of DALYs
attributable to water supply, sanitation, and hygiene in terms of percentages
of the total DALYs in each region and subregion. Again, the two estimates are
close. The proportion of the total disease burden attributable to water,
sanitation, and hygiene is greatest in the high-mortality countries of the
Eastern Mediterranean region, reaching 6 to 7 percent of the total. They are
followed by the high-mortality countries of Southeast Asia and Africa, where
the water and sanitation complex accounts for 4 to 5 percent of the total.
Globally, improvements in water supply, sanitation, and hygiene could eliminate
3 to 4 percent of the global burden of disease.
DALYs Due to Diarrhea Attributable to Poor Water Supply, Sanitation, and
Hygiene by Subregion, as a Percentage of Total DALYs.
Cost-Effectiveness
The assumptions regarding effect on diarrheal disease are summarized in table 41.7. Because the effect on diarrheal disease accounts
for the vast majority of the effect, no effort is made to apportion the costs
between their effectiveness in preventing the other diseases affected by water
supply, sanitation, and hygiene. The costs derived in this chapter are
summarized in table 41.11.
Costs Assumed for Cost-Effectiveness Calculations (US$ per capita).
The annual costs used for water supply included both the amortized
construction cost and operation and maintenance costs. Given that investments
in water supply and sanitation are made largely by other sectors (and for other
motives) than health, an alternative cost-effectiveness estimate is made that
is based only on the costs of regulation, advocacy, and promotion.
The other assumptions used to calculate the cost-effectiveness of
improved water supply—of house connections, of sanitation, and of hygiene
promotion—other than those set out above, are as described by Varley, Tarvid, and
Chao (1998). The key parameters are as follows:
- proportion of population under age five: 17 percent
- diarrhea incidence: five cases per child under age five per year
- median age at onset of disease: 1 year
- average duration: 8 days
- case fatality rate: 0.5 percent
- coverage by oral rehydration therapy: 30 percent
- oral rehydration therapy reduction in case fatality rate: 50
percent
On this basis, we arrived at the cost-effectiveness values in table 41.12.
Cost-Effectiveness of Water Supply, Sanitation, and Hygiene Promotion
(US$/DALY).
All of these figures underestimate the cost-effectiveness of investments
in water and sanitation, for several reasons:
- The effects of these interventions on diseases other than diarrhea
have not been taken into account; they seem to be relatively minor for
water supply but may be substantial if hand washing proves to affect ARI.
- Effects on diarrhea mortality, which account for 98 percent of the
DALYs, are likely to be greater than the reductions in morbidity shown in table 41.7.
- The cost figures have generally been taken so as to be sufficient
for all contexts, whereas water supply and sanitation can be implemented
more cheaply in favorable settings—such as where a convenient aquifer or
reliable rainfall exists.
- Potential economies exist in combining the interventions; for
example, sanitation promotion can be combined with hygiene promotion and
water pipes laid with sewers.
- The current global initiative to promote hand washing, involving
commercial marketing expertise, may identify more cost-effective
approaches to hygiene promotion.
- If a sustainable low-cost sanitation industry can be developed, it
will have an interest in promoting its own product.
As they stand, the cost-effectiveness values above, except for house
connections and construction of latrines, are well below the US$150/DALY cutoff
value proposed by the World Bank (1993)
as a criterion of cost-effectiveness. Allowing only for the cost component that
should fall to the health sector puts them all well within this ceiling. For
comparison, the cost-effectiveness of promoting oral rehydration therapy, the
principal other measure available to prevent diarrhea mortality, has been
estimated at US$23/DALY. The cost-effectiveness of promoting sanitation and
hygiene as derived above (US$11.15 and US$3.35, respectively, per DALY)
compares favorably with that figure.
Acknowledgments
The calculations of the burden of disease were made by Dr. D. Campbell-Lendrum,
using spreadsheets derived by Annette Prüss-Üstün. Their collaboration is
gratefully acknowledged.
References
- Allan, S. 2003. "The WaterAid Bangladesh/VERC 100% Sanitation
Approach; Cost, Motivation and Subsidy." M.Sc. dissertation, London
School of Hygiene and Tropical Medicine.
- Altaf M. A. Household Demand for Improved Water and Sanitation in a
Large Secondary City: Findings from a Study in Gujranwala, Pakistan. Habitat
International. 1994;18(1):45–55.
- Arlosoroff S., G. Tchannerl, D. Gray, W. Journey, A. Karp, O.
Langenegger, and R. Roche. 1987. Community Water Supply: The Handpump
Option. Washington, DC: World Bank.
- Bern C., Martines J., de Zoysa I., Glass R. I. The Magnitude of the
Global Problem of Diarrheal Disease: A Ten-Year Update. Bulletin of the
World Health Organization. 1992;70(6):705–14. [PMC free
article] [PubMed]
- Blum D., Feachem R. G. Measuring the Impact of Water Supply and
Sanitation Investments on Diarrheal Diseases: Problems of Methodology. International
Journal of Epidemiology. 1983;12(3):357–65. [PubMed]
- Borghi J., Guinness L., Ouedraogo J., Curtis V. Is Hygiene
Promotion Cost-Effective? A Case Study in Burkina Faso. Tropical Medicine
and International Health. 2002;7(11):960–69. [PubMed]
- Briscoe, J., R. G. Feachem, and M. M. Rahaman. 1985.
"Measuring the Impact of Water Supply and Sanitation Facilities on
Diarrhea Morbidity: Prospects for Case-Control Methods." Offset
publication WHO/CWS/85.3, World Health Organization, Geneva.
- Bukenya G. B., Nwokolo N. Compound Hygiene, Presence of Standpipe,
and Risk of Childhood Diarrhea in an Urban Settlement in Papua New Guinea.
International Journal of Epidemiology. 1991;20(2):534–39. [PubMed]
- Cairncross S. Health Impacts in Developing Countries: New Evidence
and New Prospects. Journal of the Institution of Water and Environmental
Management. 1990;4(6):571–77.
- ———. 1992. "Sanitation and Water Supply: Practical Lessons
from the Decade." Water and Sanitation Discussion Paper 9, World
Bank, Washington, DC.
- ———.2003a. Sanitation in the Developing World: Current Status and
Future Solutions International Journal of Environmental Health Research 13Suppl.
1S123–31.31. [PubMed]
- ———.2003b. Handwashing with Soap: A New Way to Prevent ARIs? Tropical
Medicine and International Health 88677–79.79. [PubMed]
- Cairncross, S., and R. Feachem. 1993. Environmental Health
Engineering in the Tropics. 2nd ed. Chichester, U.K.: John Wiley &
Sons.
- Cairncross S., Kinnear J. Elasticity of Demand for Water in
Khartoum, Sudan. Social Science and Medicine. 1992;34(2):183–89. [PubMed]
- Cairncross, S., D. O'Neil, A. McCoy, and D. Sethi. 2003. Health,
Environment, and the Burden of Disease: A Guidance Note. London:
Department for International Development.
- Cairncross S., Shordt K. It Does Last! Some Findings from a
Multi-Country Study of Hygiene Sustainability. Waterlines. 2003;22(3):4–7.
- Cave, B., and V. Curtis. 1999. "Effectiveness of Promotional
Techniques in Environmental Health." WELL Study 165, London School of
Hygiene and Tropical Medicine for Department for International
Development.
- Chavasse D. C., Shier R. P., Murphy O. A., Huttly S. R., Cousens S.
N., Akhtar T. Impact of Fly Control on Childhood Diarrhea in Pakistan:
Community-Randomised Trial. Lancet. 1999;353(9146):22–25. [PubMed]
- Churchill, A. A., D. de Ferranti, R. Roche, C. Tager, A. A.
Walters, and A. Yazer. 1987. "Rural Water Supply and Sanitation: Time
for a Change." World Bank Discussion Paper 18, Washington, DC, World
Bank.
- Curtis V., Cairncross S. Effect of Washing Hands with Soap on
Diarrhea Risk in the Community: A Systematic Review. Lancet Infectious
Diseases. 2003;3(5):275–81. [PubMed]
- Curtis V., Kanki B., Mertens T., Traore E., Diallo I., Tall F.,
Cousens S. Potties, Pits and Pipes: Explaining Hygiene Behaviour in
Burkina Faso. Social Science and Medicine. 1995;41(3):383–93. [PubMed]
- Emerson P. M., Cairncross S., Bailey R. L., Mabey D. C. Review of
the Evidence Base for the `F' and `E' Components of the SAFE Strategy for
Trachoma Control. Tropical Medicine and International Health. 2000;5(8):515–27.
[PubMed]
- Emerson P. M., Lindsay S. W., Alexander N., Bah M., Dibba S.-M.,
Faal H. B. et al. Role of Flies and Provision of Latrines in Trachoma
Control: Cluster-Randomised Controlled Trial. Lancet. 2004;363:1093–98. [PubMed]
- Esrey S. A., Feachem R. G., Hughes J. M. Interventions for the
Control of Diarrheal Diseases among Young Children: Improving Water
Supplies and Excreta Disposal Facilities. Bulletin of the World Health
Organization. 1985;63(4):757–72. [PMC free
article] [PubMed]
- Esrey, S. A., and J-P. Habicht. 1985. The Impact of Improved
Water Supplies and Excreta Disposal Facilities on Diarrheal Morbidity,
Growth, and Mortality among Children. Cornell International Nutrition
Monograph Series 15. Ithaca, NY: Division of Nutritional Sciences, Cornell
University.
- Esrey, S. A., J. B. Potash, L. Roberts, and C. Shiff. 1990.
"Health Benefits from Improvements in Water Supply and Sanitation:
Survey and Analysis of the Literature on Selected Diseases." WASH
Technical Report 66, Environmental Health Project, Rosslyn, VA, for USAID.
- ———.1991. Effects of Improved Water Supply and Sanitation on
Ascariasis, Diarrhea, Dracunculiasis, Hookworm Infection, Schistosomiasis,
and Trachoma Bulletin of the World Health Organization 695609–21.21. [PMC free
article] [PubMed]
- Ezzati M. Complexity and Rigour in Assessing the Health Dimensions
of Sectoral Policies and Programmes. Bulletin of the World Health
Organization. 2003;81(6):458–59. [PMC free
article] [PubMed]
- Feachem, R. G., D. J. Bradley, H. Garelick, and D. D. Mara. 1983. Sanitation
and Disease: Health Aspects of Excreta and Wastewater Management.
Chichester, U.K.: John Wiley & Sons.
- Feachem, R. G., E. Burns, S. Cairncross, A. Cronin, P. Cross, D.
Curtis, and others. 1978. Water, Health, and Development: An
Interdisciplinary Evaluation. London: Tri-Med Books.
- Gutiérrez G., Tapie-Conyer R., Guiscafré H., Reyes H., Martínez H.,
Kumate J. Impact of Oral Rehydration and Selected Public Health
Interventions on Reduction of Mortality from Childhood Diarrheal Diseases
in Mexico. Bulletin of the World Health Organization. 1996;74(2):189–97. [PMC free
article] [PubMed]
- Han A. M., Hlaing T., Kyin M. L., Saw T. Hand Washing Intervention
to Reduce Ascariasis in Children. Transactions of the Royal Society of
Tropical Medicine and Hygiene. 1988;82(1):153. [PubMed]
- Henry F. J. Environmental Sanitation Infection and Nutritional
Status of Infants in Rural St. Lucia, West Indies. Transactions of the
Royal Society of Tropical Medicine and Hygiene. 1981;75(4):507–13. [PubMed]
- Hoque B. A., Mahalanabis D., Alam M. J., Islam M. S.
Post-Defecation Handwashing in Bangladesh: Practice and Efficiency
Perspectives. Public Health. 1995;109(1):15–24. [PubMed]
- Huttly S. R. A., Morriss S. S., Pisani V. Prevention of Diarrhea in
Young Children in Developing Countries. Bulletin of the World Health
Organization. 1997;75(2):165–74. [PMC free
article] [PubMed]
- Jenkins, M. W. 1999. "Sanitation Promotion in Developing
Countries: Why the Latrines of Benin Are Few and Far Between." Ph.D.
thesis, University of California–Davis, Department of Civil and
Environmental Engineering.
- Kalbermatten, J. D., D. S. Julius, and C. G. Gunnerson. 1982. Appropriate
Sanitation Alternatives: A Technical and Economic Appraisal.
Baltimore: Johns Hopkins University Press.
- Lanata C. F. Studies of Food Hygiene and Diarrheal Disease. International
Journal of Environmental Health Research. 2003;13(Suppl. 1):S175–83. [PubMed]
- Loevinsohn B. P. Health Education Interventions in Developing
Countries: A Methodological Review of Published Articles. International
Journal of Epidemiology. 1990;19(4):788–94. [PubMed]
- Mascie-Taylor C. G. N., Alam M., Montanari R. M., Karim R., Ahmed
T., Karim E., Akhtar S. A Study of the Cost-Effectiveness of Selective
Health Interventions for the Control of Intestinal Parasites in Rural
Bangladesh. Journal of Parasitology. 1999;85(1):6–11. [PubMed]
- Mertens T. E., Fernando M. A., Marshall T. F., Kirkwood B. R.,
Cairncross S., Radalowicz A. Determinants of Water Quality, Availability,
and Use in Kurunegala, Sri Lanka. Tropical Medicine and Parasitology. 1990;41(1):89–97.
[PubMed]
- Moraes L. R. S., Cancio J. A., Cairncross S., Huttly S. Impact of
Drainage and Sewerage on Diarrhea in Poor Urban Areas in Salvador, Brazil.
Transactions of the Royal Society of Tropical Medicine and Hygiene. 2003;97(2):153–58.
[PubMed]
- Mukherjee, N. 1990. People, Water, and Sanitation: What They
Know, Believe, and Do in Rural India. New Delhi: National Drinking
Water Mission, Government of India.
- Murray, C. J. L., and A. D. Lopez. 1996. Global Health
Statistics. Cambridge, MA: Harvard School of Public Health for WHO and
World Bank.
- Phillips, M. A., R. G. A. Feachem, and A. Mills. 1987. Options
for Diarrhoel Disease Control: The Cost and Cost-Effectiveness of Selected
Interventions for the Prevention of Diarrhea. London: Evaluation and
Planning Centre for Health Care.
- Prüss A., Kay D., Fewtrell L., Bartram J. Estimating the Burden of
Disease from Water, Sanitation, and Hygiene at a Global Level. Environmental
Health Perspectives. 2002;110(5):537–42. [PMC free
article] [PubMed]
- Rosen, S., and J. R. Vincent. 2001. "Household Water Resources
and Rural Productivity in Sub-Saharan Africa: A Review of the
Evidence." African Economic Policy Discussion Paper 69, John F. Kennedy
School of Government, Harvard University, Cambridge, MA.
- Stanton B. F., Clemens J. D. An Educational Intervention for
Altering Water-Sanitation Behaviors to Reduce Childhood Diarrhea in Urban
Bangladesh: II. A Randomized Trial to Assess the Impact of the
Intervention on Hygienic Behaviors and Rates of Diarrhea. American Journal
of Epidemiology. 1987;125(2):292–301. [PubMed]
- Strina A., Cairncross S., Barreto M. L., Larrea C., Prado M. S.
Childhood Diarrhea and Observed Hygiene Behavior in Salvador, Brazil. American
Journal of Epidemiology. 2003;157(11):1032–38. [PubMed]
- Thompson, J., I. T. Porras, J. K. Tumwine, M. R. Mujwahuzi, M.
Katui-Katua, N. Johnstone, and L. Wood. 2001. Drawers of Water II: 30
Years of Change in Domestic Water Use and Environmental Health in East
Africa. London: International Institute for Environment and
Development.
- Traoré E., Cousens S., Curtis V., Mertens T., Tall F., Traoré A. et
al. Child Defecation Behaviour, Stool Disposal Practices, and Childhood
Diarrhea in Burkina Faso: Results from a Case-Control Study. Journal of
Epidemiology and Community Health. 1994;48(3):270–75. [PMC free
article] [PubMed]
- Varley R. C. G., Tarvid J., Chao D. N. W. A Reassessment of the
Cost-Effectiveness of Water and Sanitation Interventions in Programmes for
Controlling Childhood Diarrhea. Bulletin of the World Health Organization.
1998;76(6):617–31. [PMC free
article] [PubMed]
- Victora C. G., Smith P. G., Vaughan J. P., Nobre L. C., Lombardi
C., Teixeira A. M. et al. Water Supply, Sanitation, and Housing in
Relation to the Risk of Infant Mortality from Diarrhea. International
Journal of Epidemiology. 1988;17(3):651–54. [PubMed]
- Wagner, E. G., and J. N. Lanoix. 1959. Water Supply for Rural
Areas and Small Communities. WHO Monograph Series 42. Geneva: World
Health Organization.
- Waterkeyn, J. 2003."Cost-Effective Health Promotion: Community
Health Clubs." In Proceedings of the 29th WEDC Conference, Abuja,
Nigeria. Loughborough, U.K.: Water Engineering and Development Centre.
- White, G. F., D. J. Bradley, and A. U. White. 1972. Drawers of
Water: Domestic Water Use in East Africa. Chicago: University of
Chicago Press. [PMC free
article] [PubMed]
- Whittington D., Mu X., Roche R. Calculating the Value of Time Spent
on Collecting Water: Some Estimates for Ukunda, Kenya. World Development. 1990;18(2):269–80.
- WHO (World Health Organization). 2002. Reducing Risks, Promoting
Healthy Life: World Health Report 2002. Geneva: WHO.
- WHO and UNICEF (World Health Organization and United Nations
Children's Fund). 2000. Global Water Supply and Sanitation Assessment
2000 Report. Geneva: WHO with UNICEF.
- Wilson J. M., Chandler G. N. Sustained Improvements in Hygiene
Behaviour amongst Village Women in Lombok, Indonesia. Transactions of the
Royal Society of Tropical Medicine and Hygiene. 1993;87(6):615–16. [PubMed]
- World Bank. 1993. World Development Report 1993: Investing in
Health. New York: Oxford University Press.
- World Bank Water Demand Research Team. The Demand for Water in
Rural Areas: Determinants and Policy Implication. World Bank Research
Observer. 1993;8(1):47–70. [PubMed]
- Zaroff B., Okun D. A. Water Vending in Developing Countries. Aqua. 1984;5:284–95.
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