Supply of potable water has been affected by contamination of water sources in most developing countries. Rivers, lakes and groundwater have been polluted by industrial effluents, pesticides and fertilisers from agricultural run-off and urban waste. According to "Critical Trends', brought out by the United Nations, chronic water scarcity is common in areas where groundwater has been overdrawn for irrigation, industrial use or to meet the requirements of urban populations. Clearing of forests which increase surface run-off and reduce groundwater have worsened the situation. Many countries are fast using up their groundwater and moving from a situation of crisis to disaster.