AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
If supplies of fresh water are limited, desalination of salty water or sea…
Full specification wording
Potable water: If supplies of fresh water are limited, desalination of salty water or sea water may be required.
Some regions have limited fresh water because of low rainfall, high demand or both.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 8 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Some regions have limited fresh water because of low rainfall, high demand or both. In these situations, salty water from the sea or from underground sources may be treated by desalination to produce potable water. Desalination removes dissolved salts so the water becomes safe to drink. It is used when fresh water supplies are insufficient, for example in dry coastal areas or countries with high water demand. Desalination is expensive and uses a lot of energy, so it is not the first choice where fresh water is available. Understanding when desalination is required means linking water scarcity to the need for an alternative source and recognising that salty water must have its dissolved salts removed.
What earns the marks
- Desalination is used when supplies of fresh water are limited.
- Salty water or sea water can be treated by desalination.
- Desalination removes dissolved salts to produce potable water.
- Desalination is an alternative when fresh water sources are insufficient.
- Desalination is energy-intensive and costly compared with using fresh water.
- The need for desalination depends on local availability of fresh water.
Common mistakes and how to put them right
Thinking desalination is always used.
Put it right: It is required only when fresh water supplies are limited.
Confusing desalination with filtration.
Put it right: Desalination removes dissolved salts, whereas filtration removes insoluble solids.
Assuming sea water is already potable.
Put it right: Sea water contains high levels of dissolved salts and must be desalinated.
Exam tips
- Link desalination to the phrase supplies of fresh water are limited in your answer.
- State that desalination removes dissolved salts, not just microbes or insoluble solids.
- Mention that desalination is expensive or energy-intensive when discussing why it is not always used.
Try the lesson
The start of the Potable water: If supplies of fresh water are limited, desalination of salty water or sea water may be required. lesson, made from checked teaching notes for this specification point.
Have a go first
A country has very little rain and its rivers often run dry. What process may be used to obtain potable water from the sea?
Listen
Some regions have limited fresh water because of low rainfall, high demand or both. In these situations, salty water from the sea or from underground sources may be treated by desalination to produce potable water. Desalination removes dissolved salts so the water becomes safe to drink. It is used when fresh water supplies are insufficient, for example in dry coastal areas or countries with high water demand. Desalination is expensive and uses a lot of energy, so it is not the first choice where fresh water is available. Understanding when desalination is required means linking water scarcity to the need for an alternative source and recognising that salty water must have its dissolved salts removed. A strong answer earns marks for these points. Desalination is used when supplies of fresh water are limited. Salty water or sea water can be treated by desalination. Desalination removes dissolved salts to produce potable water. Desalination is an alternative when fresh water sources are insufficient. A common slip: Thinking desalination is always used. Instead, it is required only when fresh water supplies are limited. Exam tip: Link desalination to the phrase supplies of fresh water are limited in your answer.
Key words
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Desalination
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Dissolved salts
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Energy and cost of water treatment
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Water scarcity and supply
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See every definition
- Desalination
- A treatment used when supplies of fresh water are limited, removing dissolved salts from salty water or sea water to produce potable water.
- Dissolved salts
- What desalination removes from salty water or sea water so the water becomes safe to drink.
- Energy and cost of water treatment
- Desalination is expensive and uses a lot of energy, so it is not the first choice where fresh water is available.
- Water scarcity and supply
- Some regions have limited fresh water because of low rainfall, high demand or both, so an alternative source may be required.
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