Impact of Safe Water, Sanitation on World's Poor

Both improvements lead to better health, although how much each contributes has been hard to measure. That is because people's health is also affected by personal habits, methods of storing and cooking food, as well as by education and income.

Piped water reduces the incidence of typhoid fever -- an outcome seen both in contemporary studies and in historical analysis. In Philadelphia, for example, a study showed that as water filtration was brought to the city's six water districts between 1902 and 1909, typhoid mortality in each district fell. Between 1888 and 1912, deaths in German cities from that disease fell by 80 percent, with half of the decrease attributed to piped water.

But clean water by itself has relatively little effect on rates of other water-borne infections, such as childhood diarrhea. Those illnesses are mostly transmitted by the fecal contamination of food, dishes and hands. They reflect the amount of water a household has for washing and hygiene, not the quality of the water.

For that reason, bringing the source of water to the house or yard reduces the diarrhea rate by 44 percent, while water delivered to a public "standpipe" -- where someone must go with a water container -- reduces the rate only by 6 percent.

Improved sanitation cuts diarrhea incidence by a quarter to a third. Interventions that promote personal hygiene, such as hand washing, decrease it by 42 percent, according to a recent analysis of studies by Lorna Fewtrell of the University of Wales and Jack M. Colford of the University of California at Berkeley.

Traditional water-borne diseases, however, are not the only ones reduced by clean water and toilets.

Trachoma is a bacterial infection of the eyelid responsible for about 6 million cases of blindness worldwide. Better water and sanitation reduces trachoma rates by an average of 27 percent. Once-a-day face washing with a handful of water is one of the four chief interventions being pushed in an international effort to eliminate trachoma.

Curiously, health benefits are far down the list of reasons that people in poor countries give for wanting better water and sanitation services. Relief from the drudgery of carrying water long distances -- a chore borne almost entirely by women and girls -- is the chief benefit that people mention.

A 2002 UNICEF study of rural households in 23 sub-Saharan countries found that a quarter of them spent 30 minutes to an hour each day collecting and carrying water, and 19 percent spent an hour or more. With closer water comes greater self-esteem, less harassment of women, and better school attendance by girls -- three things spontaneously mentioned by people in Ethiopia, Ghana, Tanzania and India in a different study.

Toilets are similarly liberating. In many cultures, rural women venture out to urinate and defecate only at night.

In a study of 320 households in the West African nation of Benin, people were asked to rank the benefits of owning a latrine on a scale of 1 to 4. "Avoid discomforts of the bush" came in at 3.98. "Gain prestige from visitors" was 3.96. "Avoid snakes" was 3.85.

"Health" was 1.27.