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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.

For 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 dissolved salt present in sea water requires a lot of energy.

Rain provides water with low levels of dissolved substances. In the UK, rain provides sufficient water to meet the needs of the population, although sometimes it needs to be stored and transported. Sometimes during the summer months in some areas of the UK, water reserves run low and hosepipe bans are used to encourage people to conserve water. Most potable water in the UK is produced from naturally occurring fresh water by:

1. choosing an appropriate source of fresh water
2. passing the water through filter beds to remove insolubleparticles
3. sterilising the water to kill microbes

The methods used for sterilisation include chlorine, ozone and ultraviolet light.