Tall buildings may also need to store water locally in pressure vessels in order for the water to reach the upper floors. Water purification usually occurs close to water supply distribution system pdf final delivery points to reduce pumping costs and the chances of the water becoming contaminated after treatment.
Traditional surface water treatment plants generally consists of three steps: clarification, filtration and disinfection. Sand, anthracite or activated carbon filters refine the water stream, removing smaller particulate matter. While other methods of disinfection exist, the preferred method is via chlorine addition. Chlorine effectively kills bacteria and most viruses and maintains a residual to protect the water supply through the supply network. The water is typically pressurised by pumps that pump water into storage tanks constructed at the highest local point in the network.