The current use of the freshwater resowxs in many parts of the wwld is snot sustainable. PI-cw~tly. about we-thit~d 01 the world population is living in areas suffering from moderate to severe water stress, i.e.. where water limits the possibilities of economic and social development. Unlcs? actions are taken. up to two-thirds of the world population. or clox to 5.5 billion people, will be at risk of facing this situation by 2025. At the same time, it is of uttnost importance to leave enough clean water to preserve aquatic and terrestrial ecosystems. Water quality is deteriorating due to pollution from almost all human activities. As an example can be mcntioned that most cities in the developing world still treats less than IO per cent of the sewage. In 1995, 20 per cent of the world population lacked access to safe drinking water and as much as SO per cent lacked access to adequate sanitation. In order to provide all people of the world with access to sanitation by 2025, five billion will need to be served over the next 30 years, or about 450,000 each day.