Water is the essential ingredient for all plant and animal life on earth, yet millions of people perish or fall ill because they do not have enough. And all too often available supplies are contaminated or disease-ridden. Two additional and increasingly significant problems are the short-term devastation that drought can bring and the longer-term consequences of ‘desertification’, whereby fertile land turns to desert.

Of all water on earth, 97.5 per cent is salt water, and of the remaining 2.5 per cent that is fresh water some 70 per cent is frozen in polar icecaps. The other 30 per cent is mostly present as soil moisture or lies underground. This leaves about 0.007 per cent of all water available for direct use by humans.

One of the primary tenets of the World Health Organisation (WHO) and its member states is that “all people, whatever their stage of development and their social conditions, have the right to have access to an adequate supply of safe drinking water”. With that in mind, a WHO report reveals that over 1 billion people do not have access to an adequate supply of safe water for household consumption, while nearly three billion lack a sanitary means of sewage disposal. The WHO also estimates that 250 million people worldwide have been directly affected by desertification and that nearly one billion are at risk.

Water contamination by human, chemical or industrial waste is a global problem and can cause a variety of communicable diseases through ingestion or physical contact. The WHO classifies these as waterborne, water-washed, water-based and water-related diseases.

Waterborne diseases are caused by the ingestion of water contaminated by human or animal faeces or urine containing pathogenic bacteria or viruses. These include cholera, typhoid, amoebic and bacillary dysentery, and other diarrhoeal diseases. Water-washed diseases are caused by poor personal hygiene and skin or eye contact with contaminated water. Included here are scabies, trachoma, and flea, lice and tick-borne diseases.

The cause of water-based diseases comes from parasites found in organisms living in water. Water-related diseases caused by insect vectors, which breed in water, include dengue fever, malaria and yellow fever.

According to the WHO, no single type of intervention has greater overall impact upon a nation’s development and public health than the provision of safe drinking water and the proper disposal of human excreta. Water supply and sanitation systems have been badly neglected in developing countries for years, often due to a combination of poor organisation of suppliers, lack of spare parts, inappropriate technology and insufficient funds.

The direct effect of improved water and sanitation services on health are clearly seen in the case of water-related diseases, which arise from the ingestion of pathogens in contaminated water or food and from insects or other vectors associated with water. Improved water and sanitation can reduce the morbidity and mortality rates of the most serious of these diseases by 20 and 80 per cent.

But some problems go much deeper that that. High levels of arsenic are often found in water that has flowed through arsenic-rich rocks, for instance. Long-term exposure to arsenic can cause cancer of the skin, lungs, bladder and kidney, as well as skin changes such as thickening and pigmentation. Severe health effects have been observed in populations worldwide drinking arsenic-rich water over long periods.

Examples of many countries where arsenic in drinking water has been detected at concentrations greater than WHO guidelines include Argentina, Australia, Bangladesh, Chile, China, Hungary, India, Mexico, Peru and Thailand. In the US, the Environment Protection Agency has estimated that some 13 million people, mostly in the western states are exposed to arsenic in drinking water, although concentrations appear to be lower in places like Bangladesh and West Bengal. Information on arsenic in drinking water on a country-by-country basis is currently being collected by the United Nations and added to a UN report on arsenic in drinking water.*

Water in swimming pools, lakes and seas can also be contaminated or carry disease. Anything from microbiological hazards and chemicals to freshwater and marine algae can cause contamination. Some recreational waters may carry warnings. Swimmers at the Serpentine Lake in London’s Hyde Park, for instance, are warned about every-thing from botulism and poliomyelitis to green algae and Weil’s disease – the latter caused by micro-organisms that arise in the urine of rats and farm animals and can lead to a flu-like illness, fatal in as many as 2 per cent of cases. But while warnings for swimming in some countries may be good, in others they might not. In an East African lake there may be no notification about the potential risk of say, bilharzia.

For further information, see: www.who.int/wate_sanitation_health/dwq/arsenic/en/