Purifying water

• What does good water contain?

  • Low levels of dissolved salts
  • Low levels of microbes
• What stages do water companies go through?

  • A fresh and unpolluted source is selected, freshwater doesn't contain salt but seawater does
  • Filtration then occurs. It involves spraying water onto layers of sand. This removes and dirt and stones from the water
• What dangerous pollutants can end up in water and how?

  • Pesticides and nitrates (fertilisers) are washed off farmland by rain and into water supply, water companies need to make sure that their water is filtered.
  • Lead compounds are another pollutant that can be washed into water from old pipes, paint or factory waste
• What stages do water companies go through? Pt.2

  • Then sedimentation occurs. The filtered water still contains thin, solid particles that can still pass through the filters. A chemical is added that clumps the solid particles together. The particles settle at the bottom of the container forming a sediment or they can be removed by prefiltering.
• What stages do water companies go through? Pt.3

  • The water is then chlorinated. It involves treating the water with chlorine gas. It sterilisers water killing off any microbes. Chlorination has made a significant impact to public health by reducing deaths from any water borne diseases such as cholera. A disadvantage is that it can spoil the taste of water.
• Trihalomethanes


  • When chlorine reacts with organic substances
  • They have been linked with causing cancer
• Fluorination


  • In some areas, this is a step to making water safe for the public
  • Fluorination means purifying the water and fluoride is added
  • Evidence proves that adding fluoride to drinking supplies, it has lowered the amount of dental cavities and it has improved overall dental health
  • Fluoride has been argued against because it may reach toxic levels in consumption of water. It has been done against our will
• What is also a source of drinking water in dry countries

  • The sea
  • Dry countries such as Saudi Arabia uses the sea as a water supply
  • Sea water contains a lot of dissolved salts meaning it needs to be distilled
  • A disadvantage is that a lot of energy is required to evaporate the water and leave the salt behind
  • Many countries that use this method today result in natural heat sources to conserve energy and modern technologies to heat the water