Sources of potable water

• Water that is safe to drink is called potable water. Potable water is not pure water in the chemical sense because it contains dissolved substances.
• The methods used to produce potable water depend on available supplies of water and local conditions.
• In the UK, rain provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers and most potable water is produced by: • choosing an appropriate source of fresh water • passing the water through filters • sterilising.
• Sterilising agents used for potable water include chlorine, ozone or ultraviolet light.
• If supplies of fresh water are limited, desalination of salty water or sea water may be required.
• Desalination can be done by distillation or by processes that use membranes such as reverse osmosis. Energy resources have to be used to run these processes.
• Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment.
• Sewage and agricultural waste water require removal of organic matter and harmful microbes. Industrial waste water may require removal of organic matter and harmful chemicals
• Sewage treatment includes: • screening and grit removal • sedimentation to produce sewage sludge and effluent • anaerobic digestion of sewage sludge • aerobic biological treatment of effluent.