Potable Water

•  Potable water is not pure water, because it contains dissolved substances.
• Water that is safe to drink is called potable water. 
• One way of obtaining drinkablewater with low levels of dissolved substances (fresh water) is by collecting the water in the ground and in lakes and rivers. To make this water potable, it must go through these steps:

  1. sedimentation - solids sink to the bottom and are removed
  2. filtration - fine particles like sand are removed
  3. sterilisation - microbes are killed (sterilising agents used for potable water include chlorine, ozone or ultraviolet light)
• If supplies of fresh water are limited (such as on an small island), desalination of sea water (high salt levels) may be required. Desalination can be done by distillation or by processes that use membranes such as reverse osmosis. These processes require large amounts of energy.
• water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. This can help separate the salt from salt water.
• Potable water

  Water that is safe to drink
• Pure water

  Water that contains no dissolved substances at all
• Drinking water must have sufficiently low levels of dissolved salts such as sodium chloride and low levels of microbes such as bacteria
• Producing potable water from fresh water

  1. Use a good source of fresh water

  2. Pass the water through filter beds to remove material such as leaves and suspended particles

  3. Sterilize the water to kill microbes (using chlorine, ozone or ultraviolet light)
• Producing potable water from salty water

  1. Use desalination to reduce the levels of dissolved minerals (through distillation or reverse osmosis)

  2. Both distillation and reverse osmosis require large amounts of energy, making them expensive
• In the UK, rain water provides most of the potable water, which collects in aquifers, lakes, rivers and reservoirs
• In many places, fresh water is scarce, so the only available water may be too salty to drink, such as seawater