29.1-Potable Water

Water is essential for life

• Water that is safe for humans to drink is called potable water.

• Potable water is not pure water because it almost always contains dissolved impurities.

• or water to be potable, it must have sufficiently low levels of dissolved salts and microbes. This is because:

  • Dissolved salts can sometimes be harmful for humans

  • Microbes can cause illnesses

Potable water in the UK

• The methods used to make water potable depend on where you live.

• Starting with fresh water is easier than sea water, as removing the large amount of sodium chloride present in sea water requires a lot of energy.

• In the UK, rain provides enough fresh water to meet the needs of the population.

• Sometimes during the summer months in some areas of the UK, water reserves run low and people are encouraged to conserve tap water by the use of hosepipe bans.

• Rainwater collects in rivers, lakes and in rocks underground.

  • This water contains low levels of dissolved substances.

• Most potable water in the UK is produced from naturally occurring fresh water by:

1. passing the water through filter beds to remove insoluble particles

2. sterilising the water to kill microbes

Practice Problems:

• Describe the steps you could take to treat water from a groundwater source to make it potable?

  • Filter the water first, using a wire mesh followed by sand and gravel beds

  • Then sterilize the filtered water using chlorine/ozone/UV radiation

• Potable water definition?

  • Water that’s been treated or is naturally safe for humans to drink, but it wouldn’t be called pure water in the chemical sense as it contains lots of other dissolved substances

29.2-Waste Water Treatment

In the environment:

• Waste water from homes, industry and agriculture must be treated before being released into the environment.

• Here are some examples of pollutants which might be present in waste water:

  • human waste contains harmful bacteria and high levels of nitrogen compounds which can harm aquatic ecosystems

  • industrial waste water may contain harmful chemicals such as toxic metal compounds

  • agricultural waste water may contain fertilisers or pesticides which can disrupt sensitive ecosystems

• Sewage treatment involves the following steps:

1. Screening and grit removal to remove large particles

2. Sedimentation allows tiny particles to settle out from still water, which produces sewage sludge and effluent (the liquid which remains on top)

3. The sewage sludge is digested anaerobically by specific bacteria

4. The effluent is treated with aerobic bacteria to reduce the volume of solid waste

Practice Problems:

• List three stages of treatment that domestic sewage undergoes at a sewage treatment plant

  • Screening

  • Sedimentation

  • Digestions

• What is sedimentation?

  • Process that allowed tiny particles to settle out from still water

  • Which produces sewage sludge and effluent(which a liquid that remains on top)