Water management refers to the management of both water inputs and water outputs in the city. Cities need to have robust water management systems in place to provide their residents with clean water as well as to keep the city clean. The type of water management systems in cities largely depend on the natural landscape of the city as well as its level of development. However, they can be broadly categorised as closed (recyclatory) and open (constant water input) systems. Water management systems include water sources (e.g. groundwater, sea water, reservoirs), other material inputs (e.g. manpower, natural resources), service inputs (e.g. water treatment, sewage treatment, finance, accounting, research & development, logistics and regulatory agencies).