Over 80% of all illness in the developing world is directly or indirectly associated with poor water supply and sanitation. The lack of these fundamental services provokes great centres of infection, which are characteristic of the developing countries. Large water development schemes, dams and irrigation, invariably favour the spread of diseases, if the projects are not implemented with proper drainage and water management systems. Occupational contact with free standing water, as lake fishing and rice farming, also exacerbates the spread of certain diseases. Onchocerciasis, transmitted through the larvae of a black fly vector breeding in watercourses, causes visual impairment and blindness. Trachoma, considered to be the single most important cause of preventable blindness in the world, is common under conditions of poor hygiene, sanitation and nutrition. Filariasis, cholera and bacterial enteric infections, the latter a major cause of death among children in the tropics, are also related to water supply and sewage facilities. Skin infections, trachoma, guinea worm and schistosomiasis are some of the other diseases transmitted by water.
[Developing countries] Everyday, over 30,000 people in the developing countries die as a result of inadequate water supply and sanitation. Lack of safe water is the start of a tragic disease cycle; millions of people are unable to work due to water-related diseases, and countless are crippled, blinded or maimed for life. It is estimated that the majority of people in developing countries use domestic water from sources that are subject to contamination. For example, in 5 villages from widely separated parts of India it was found that from 23% to 75% of the people were infected with roundworm, hook worm, pin worm, dwarf tapeworm and intestinal amoebas. Many villagers are consequently sick a great deal of the time. They are unable to absorb all the food the eat because of the damage done by parasites to the intestinal membranes and because part of their food goes to feed the worms and protozoa that infest their intestines. Malaria, a parasitic disease reported to be increasing, is transmitted through insect vectors breeding in water. In developing areas there are 514 million people still without specific protection against this disease, and about 60% of them live in the African region. Schistosomiasis is a water-based disease, common in regions lacking water supply and sanitation facilities. According to WHO estimates, more than 600 million people are exposed to the disease, and some 200 million people in the developing countries are suffering from it. In some Latin American cities 60% of the children die before the age of 5 because of water-borne diseases.