Megacities, i.e., cities with more than ten million residents are growing fast. In developing countries, and especially in Africa the growth is fastest. Water-related problems in these cities are already enormous, and further degradation is expected. Water shortage is a rapidly growing problem and delivery of safe drinking water cannot be ensured. In many places municipal and industrial wastes are disposed of to the natural environment, generally without adequate treatment. Infrastructure and wastewater treatment facilities are usually by far insufficient. The present situation with respect to pollution of ail; land, and water, as well as lack of basic water and sanitation facilities in these cities creates living conditions that are nothing less than a derision of human dignity. Megacities constitute the most important source of global environmental pollution. Solution of this megaproblem of megacities requires efficient regulations and actions to stop further population growth and, in the water sector to develop novel environmentally friendly and economically efficient methods of water conservation and treatment. A vicious cycle of losing nutrients and carbon in agriculture, causing land degradation, hunger and urban migration, cannot be broken by traditional technology. Improvements that can break this cycle cannot be accomplished without local initiatives and the active participation of the local population. Development of a novel approach and a new technology of urban water management that is economically affordable for developing countries and more environmentally sound is necessary. Technological change must be accompanied by basic changes in all sectors, social and central structures, educational and research programs, and in lifestyle.