More water, better health

Posted: 16 August 2000

Author: Sandy Cairncross

Author Info: Sandy Cairncross, an engineer and epidemiologist, is Professor of Environmental Health at the London School of Hygiene & Tropical Medicine.

For nearly 100 years, public health workers have generally believed that the most important advantage of a good water supply is that it is safe from contamination. Mothers of small children in poor communities around the world have long known better. To them the most important advantage is that it is convenient and provides enough for their needs. Sandy Cairncross reports.

Only in the last decade or so have public health workers and engineers come to understand that improved convenience and quantity of water available can bring greater benefits to the users than improvements in quality.boy with waterTonga Child carrying water from a well, Zimbabwe© Neil Cooper/Panos PicturesThis is true, even though many different infectious diseases are related to water in a variety of ways. These can be grouped into four categories.

The most common and important are Faecal-oral which are caused by micro-organisms (such as bacteria or viruses). These are present, usually in vast numbers, in the faeces of infected people. One only needs to swallow a few to have a chance of falling ill, so that if microscopic amounts of faecal material from one person reach the mouth of another, the disease can be passed on. Most of them cause diarrhoea. They kill over three million children a year, mostly under five years old. Some of these diseases, such as cholera and typhoid fever, are famously described as "water-borne diseases". However this is a misnomer, as drinking water is only one way in which they can be transmitted. All of the faecal-oral infections can also be passed on by contaminated food, fingers, utensils and even clothes. One study in Dhaka, Bangladesh found that poor women sometimes used the corner of their sari to wipe the dishes, clean their child's face, and even to clean his bottom! Disease transmission in ways such as this can be prevented by having more water available in the home to keep things clean. Water-washed skin and eye diseases have little to do with water quality. They are most common in arid areas where water for household use requires hours of drudgery to carry it home, or a heavy payment to a water vendor. For them too, more water, readily available, is the best preventive measure. Some of these diseases can have very serious effects; for example, trachoma can cause permanent blindness - a terrible fate to suffer in the Third World.

Water-based diseases are caused by certain parasitic worms which cannot pass directly from person to person, but must first develop in another animal which lives in water, usually a snail. The most famous of these is schistosomiasis (bilharzia), which is caught by wading or swimming in infected water. Even a tap in the backyard is unlikely to prevent this, unless it prevents children from swimming in the local pond on a hot day. Water-related insect vector diseases are spread by insects which breed in water (such as mosquitoes) or bite near to rivers. The different types of insect responsible for each disease in each part of the world prefer different bodies of water in which to breed. One type, for example, breeds in the water storage tanks on large buildings in Indian cities, and transmits malaria; another likes septic tanks and puddles of waste washing water, and transmits a disfiguring condition known as elephantiasis, in Asia, East Africa and coastal Brazil. Water supplies do not often help to control these; rather, they can make things worse. The greatest public health benefit from improved water supplies is the reduction in faecal-oral diseases. It has been estimated that of the deaths and hospital admissions in East Africa which can be prevented by water supplies, 90 per cent and 50 per cent respectively are in the faecal-oral category.

Engineers in the Third World therefore need to ask whether the faecal-oral infections are mainly water-borne (due to poor water quality), or mainly transmitted by food, fingers and other such "water-washed" routes (related to water quantity). Should they spend the scarce funds available for water supply on better water treatment to improve quality, or on more and bigger pipes and water sources, to increase quantity?

This has not been an easy question to answer. It is not possible to catch a micro-organism in flagrante delicto at the moment when it infects somebody; by the time someone gets ill, the contaminated water has usually been drunk, the food eaten, the hands washed. Nevertheless, research in recent decades has underlined the importance of general domestic hygiene.

For example, a few years ago a Bangladeshi epidemiologist persuaded the families of some dysentery patients to wash their hands with soap before handling food, and after defecation; this simple measure, he found, prevented 85 per cent of cases of dysentery in these families. By contrast, a Brazilian team persuaded poor households to disinfect the water in their storage pots with chlorine. Tests showed that the water was being disinfected correctly, but these families had no less diarrhoea than others who drank heavily contaminated water. Drinking water from school faucet, Kenya© Sean Sprague/Panos Pictures

Of course, this does not mean that water quality is unimportant; everyone knows that contaminated water can cause serious epidemics, because large numbers of people drink from the same supply. Rather, the endemic disease which is the day-to-day reality of poor families around the Third World, and particularly affects their small children, is unlikely to be reduced by better water quality. How can people living in poverty, who may hardly be able to afford soap, be encouraged to be more hygienic? One way is to make water more easily available to them. One would at first think that providing water closer to home would lead people to use more of it; but surprisingly, this is only true in certain cases.

If the water is originally more than 1 km away, then bringing it closer will increase the amount used. However, at about that distance (or when a round trip time to collect water takes about 30 minutes) a plateau is reached and the level of use stays constant. Only when water is within a few yards of the house, on the plot or even piped indoors, does consumption increase. Then it doubles or trebles.

Why should this be? Perhaps we need to explain the changes in consumption, rather than the plateau. A mother on the plateau keeps a container of water in her kitchen; when it is empty, she goes and fills it. There is a qualitative difference from one beyond the plateau; since water collection takes more than half an hour, she plans it for a particular point in her day, and if the water starts to run out before then, she economises. On the other hand, when one has water available in the house or yard, there is another qualitative change; one uses the water directly at the tap or pump.

Policy implications The first lesson for policy-makers is that households and communities which will benefit most from improved water supply are those farthest from their existing sources of water. Not only will their health show the greatest improvements (through the reduction of facecal-oral and water-washed skin and eye diseases); they will also benefit most from the saving in women's time and drudgery spent collecting water and carrying it home. Many poor households pay substantial amounts for water delivered to their door, which shows that their time has a money value.

Second, if all are already on the plateau, the provision of water at public taps or pumps, however, pure, is unlikely to produce any substantial health benefit, though they will of course be glad of the convenience. (An exception to this rule is where Guinea worm is common, as this water-based disease is only caught from drinking water. Guinea worm disease is rarely found outside the Sahel belt of Africa, and a campaing to eradicate it is making rapid progress).

Third, in-house connections are well worth considering if they are affordable and enough water is available to meet the increased demand they will generate. Not only can they be justified on health grounds. A sceptical World Bank economist found some years ago that the value of time spent carrying water was enough to justify house connections in most typical circumstances, regardless of any health benefit.

A further advantage is that people appreciate them so much that they are more willing to pay for them; and it is easier to collect the revenue, because non-payers can be disconnected. Studies in Latin America, also by a World Bank team, have shown that provision of free water at public stand-pipes has neglibile effect on the demand for house connections.