Water and energy are inextricably linked. Water is needed to generate energy and energy is needed to extract, treat and distribute water and to clean the used and polluted water. This is the water-energy nexus and as a consequence both challenges must be addressed together. Energy, water and environmental sustainability are closely interrelated and are vital not only to the economy but to the health and welfare of all humans .. Sustainable solutions require that we do not address singles issues in isolation, but have to adopt a systems approach with integrated solutions. The whole system has to be considered, including pure water resources, energy consumption, water usage, wastewater treatment, water reuse, receiving water and possible energy production. Still it must be remembered that technology offers only part of the solution. The attitude towards water consumption may be the crucial ingredient. Furthermore, new approaches to financing, managing and maintaining systems must be developed.