While the new industrial water conservation programs recently been adopted by the Taiwan, have been remarkably successful, few notice the inter-relationship between domestic water use and energy consumption, particularly in urban residential buildings. Energy consumption for residential water supply and drainage systems involves numerous variables. This study merely presents an overview of residential water use, and provides a simple equation for analyzing energy consumption with regard to the electric power of urban water treatment systems. Electricity consumption by house pumps is relatively minimal, and is frequently overlooked by the general public. In fact, the city shoulders the bulk of the energy costs of supplying water to citizens, with its electricity expenses per unit of water delivered being six times higher than those of a house pump. This phenomenon also indicates that water saving is crucial to energy conservation. Accordingly, residential water use consumes significant energy. On the other words, it means that raising public awareness of water conservation can also achieve significant energy savings.