Drinking Water

• Water of the correct quality is essential for life
• Water naturally contains microorganisms and dissolved salts
• Why do microorganisms and dissolved salts in water need to be at low levels?

  To be safe for humans to drink
• What type of water contains low levels of dissolved salts?

  Fresh water
• What is the name given to water that is good quality and safe to drink?

  Potable
• In the UK, how is potable water produced?

  Fresh water from a suitable source (e.g. lake) is collected - It is passed through a filter bed to remove solid particles - Chlorine gas is added to kill any harmful microorganisms - Fluoride is added to drinking water to reduce tooth decay
• Too much fluoride can cause discolouration of teeth
• What other thing can be used to sterilise water?

  Ozone and ultraviolet
• How can you improve the taste and quality of tap water?

  More dissolved substances can be removed by passing the water through a filter containing carbon, silver and ion exchange resins
• What can be done if fresh water supplies are limited?

  Seawater can be desalinated to produce pure water - this can be done using distillation or reverse osmosis
• Using distillation or reverse osmosis to produce pure water requires a lot of energy - this makes these 2 processes very expensive
• Describe what happens when distillation is used to desalinate seawater?

  The water is boiled to produce steam . The steam is condensed to produced pure liquid water