In the developing countries, water scarcity and indiscriminate disposal of industrial wastes together account for a general crisis. Freshwater sources such as the lakes, rivers and ponds have been disposal sites for domestic wastes, industrial solid and chemical wastes. Bathing, washing clothes and open defecation all go to make these sources highly polluted and these have become daily occurrences as well. These sources are indeed the sources of drinking water for several communities. Hence, 80 per cent of all diseases spread through water. Particularly, diarrhea is the most dangerous disease of the developing countries. This disease afflicts a large number of children below five years of age.
Health of humans is affected because of water pollution, quality deterioration, scarcities and water caused diseases. Diseases that affect human may be conveniently classified as five types, following the World Health Organisation, as shown below.
1. Water-breeding insects such as mosquitoes carry malaria, filariasis and yellow fever. Blackflies transmit river blindness via a parasitic worm. Water-breeding diseases: malaria, filariasis, yellow fever, blackflies and river blindness. Malaria carried by mosquitoes, affects perhaps 160 million people at any one time. There are an estimated 800 million infections each year.
2. Water-washed Diseases such as scabies, trachoma and leprosy and conjunctivitis attack the skin and eyes. All are spread by insufficient water for personal hygiene. Water-washed diseases are scabies, leprosy, conjunctivitis and trachoma
3. Water-based Diseases carried by invertebrates. Schistosomiasis is transmitted by snails; guinea worm is a parasite of a crustacean water flea. Schistosomiasis has been linked to spread of irrigation canals and reservoirs, a veritable habitat for snails. 600-1000 working days are lost per case.
4. Waterborne Diseases are spread by drinking or washing in contaminated water. Diseases include typhoid, cholera, dysentery and diarrhoea. Diarrhoea kills 6 million children every year. Repeated attacks exacerbate malnutrition, reducing food intake and impairing absorption.
5. Defective Sanitation aids the spread intestinal worms. Eggs are excreted in human faeces. The infection cycle begins on swallowing the eggs. Hookworm larvae usually enter humans by burrowing through the soles of the feet. Heavy infestations can cause death in children.
6. Trachoma is a contagious inflammation of the inner lining of the eyelids. This often causes blindness. Some 500 million people in the world suffer due to the severity of these diseases.
In the countries of the North (developed), 9 out of 10 people have ample clean, piped water and sanitation. In the South (developing and underdeveloped), only 2 out of 5 people have easy access to safe water and 1 in 4 to proper sanitation. The provision of clean and adequate supplies of water is one of the major problems of humanity in the developing world today. Rivers, lakes and ponds serve both as a source of clean water and as a sink for all wastes generated by humans. Dirty water is believed to be the principal transmission agent for at least 80 per cent of the diseases which afflict the developing countries. The rural poor, who lack access to standpipes, have little choice but to collect their water from rivers, streams, ponds, mud holes and wells. Millions of women and children often spend 6 hours a day walking long distances to bring home a few litres of dirty water. Water scarcities thus call for a concern for water supply and overcoming scarcities of any type.