Water is one of the basic necessities of life. Without one to two liters of water per day a human being cannot survive. And, to lead a minimal human existence, one needs between 20 and 50 liters of water per day for drinking, the preparation of food, and personal hygiene. For many people, this bare minimum is unattainable, because clean water is scarce.

Although two-thirds of the earth's surface is covered by water, only 0.8% is available for human beings to use - and even this small fraction is largely contaminated. More than half the population of the Third World have no adequate access to clean drinking water three-quarters have no sanitary facilities.

The rural population is especially affected. Polluted water and fecal matter are the main factors responsible for the spread and transmission of infectious diseases in the Third World, some of the consequences of which are short life expectancies, high rates of infant mortality, high costs of medical care, and low productivity.

The United Nations have declared 1981 - 1990 the International Decade of Water - the goal of which is to provide all of both the urban and rural populations with clean drinking water and adequate sanitary facilities within this time period, giving precedence to those areas most neglected - namely, rural areas and urban slums.

Table 1: Number of people in the Third World (mill.) without access to clean water and sanitation (excluding China); see [1, 2, 3].