Water-related diseases are a growing human tragedy, killing more than 5 million people each year - 10 times the number killed in wars. About 2.3 billion people suffer from diseases linked to dirty water.

Some 60 per cent of all infant mortality worldwide is linked to infectious and parasitic diseases, most of them water-related.

Adverse human health effects from water can be divided into four main categories:

Water-borne diseases
Those caused by water that has been contaminated by human, animal, or chemical wastes.

Water-borne diseases include cholera, typhoid, shigella, polio, meningitis, hepatitis A and E and diarrhoea, among others. These are dirty water diseases. Most of them can be prevented if water is treated before use.

Diarrhoeal diseases
 Every day, diarrhoeal diseases cause some 6,000 deaths, mostly among children under five.
 In 2001, 1.96 million people died from infectious diarrhoeas; 1.3 million were children under five.
 Diarrhoel diseases have killed more children in the past ten years than all the people lost to armed conflict since World War II.
 Between 1,085,000 and 2,187,000 deaths due to diarrhoeal diseases can be attributed to the 'water, sanitation and hygiene' risk factor, 90 percent of them among children under five.
 In China, India and Indonesia, twice as many people die from diarrhoel diseases as from HIV/AIDS.
 With simple hygiene measures such as washing hands after using the toilet or before preparing food, most of these deaths are preventable.

Water-based diseases
Those caused by aquatic organisms that spend part of their life cycle in the water and another part as parasites of animals.

Water-based diseases include guinea worm, paragonimiasis, clonorchiasis and schistosomiasis. These diseases are caused by a variety of flukes, tapeworms, roundworms and tissue nematodes, often referred to as helminths, that infect humans. Although these diseases are not usually fatal they prevent people from living normal lives and impair their ability to work.

The prevalence of water-based diseases often increases when dams are constructed, because stagnant water behind dams is ideal for snails, the intermediary host for many types of worms. For instance, the Akosombo Dam, on Volta Lake in Ghana and the Aswan High Dam on the Nile in Egypt have resulted in huge increases of schistosomiasis in these areas.

Schistosomiasis (bilharziasis)
 Of the 200 million people in the world infected with the worm that causes schistosomiasis, some 20 million suffer severe consequences. The disesase is still found in 74 countries.
 Studies show that the disease has been cut by 77 per cent in some areas through providing better water and sanitation access.
 88 million children under fifteen years are infected each year with schistosomes.
 80 percent of transmission takes place in Africa south of the Sahara.

Water-related vector diseases
Those transmitted by vectors, such as mosquitoes and tsetse flies, that breed or live in or near polluted and unpolluted water.

Millions of people suffer from infections transmitted by vectors, such as mosquitoes and flies. Such vectors infect humans with malaria, yellow fever, dengue fever, sleeping sickness and filariasis. Malaria, the most widespread, is endemic in 100 developing countries, putting some 2 billion people at risk. In sub-Saharan Africa alone, malaria costs and estimated $1.7 billion a year in treatment and lost productivity.

The incidence of these diseases appears to be increasing. There are many reasons: people are developing resistance to antimalarial drugs; mosquitoes are developing resistance to DDT, the major insecticide used; environmental changes are creating new breeding sites; and migration, climate change, and creation of new habitats mean that fewer people build up natural immunity to these diseases.

Malaria
  About 90 percent of the annual global rate of deaths from malaria occur in Africa south of the Sahara.
 Malaria causes at least 300 million cases of acute illness each year
 The disease costs Africa more than US$12 million annually and slows economic growth in African countries by 1.3 percent a year.
 Sleeping under mosquito nets would be one simple but effective way to prevent many cases of malaria, especially for children under five.

Water-scarce diseases
Those diseases that thrive in conditions where freshwater is scarce and sanitation poor, such as trachoma and tuberculosis.

To serve the additional 5 billion people expected to live on the planet by the year 2050, there is a need to provide sewerage facilities to 383,000 new customers a day.

These diseases are becoming rampant throughout the world. They can be controlled easily through better hygiene, but adequate supplies of clean freshwater must be available.

Source: People and the Planet, World Water Assessment Programme