Potable water: Water that is safe to drink is called potable water.

The idea

Potable water is water that is safe for humans to drink. It is not the same as chemically pure water, because it can contain low levels of dissolved substances and microbes, provided these are sufficiently low to be safe. The term 'potable' is used to distinguish drinking water from other water, such as sea water or waste water, which may be unsafe.

For example: Tap water in the UK is potable: it has been treated to remove solids and kill microbes, but it still contains some dissolved ions.

What earns the marks

• Defines potable water as water that is safe to drink.
• Distinguishes potable water from chemically pure water.
• States that potable water may contain low levels of dissolved substances and microbes.
• Uses the term 'potable' correctly in written answers.
• Recognises that potability depends on safety standards rather than absence of all impurities.

Common mistakes and how to put them right

• Defining potable water as pure water.

  Put it right: Potable water is safe to drink and may contain dissolved substances.

• Using 'potable' to mean 'portable'.

  Put it right: Potable means safe to drink.

• Assuming all clear water is potable.

  Put it right: Clear water may still contain harmful microbes or dissolved salts.

Exam tips

• Learn the definition word-for-word: water that is safe to drink.
• In explanations, contrast potable water with pure water to show the difference.
• Use the term 'potable' rather than 'drinking water' when the question asks for the scientific term.
• If asked to identify potable water, look for evidence of safety, not just clarity.