Potable water is suitable for drinking. It normally contains small amounts of dissolved substances, so it is not chemically pure water.
Much of the UK’s drinking water comes from fresh-water sources. AQA describes filter beds and sterilisation, including chlorine, ozone or ultraviolet light. Edexcel names sedimentation, filtration and chlorination for waste and ground water.
Salt water requires desalination to remove dissolved salts. AQA names distillation and membrane processes such as reverse osmosis. Edexcel names seawater distillation and also requires water used in analysis to contain no dissolved salts. A filter bed alone does not remove dissolved sodium chloride.
The residue left after evaporating a water sample gives information about dissolved non-volatile material. The result cannot, by itself, establish whether the sample is safe to drink.
Worked example
A 100 cm³ water sample leaves 0.03 g of dry residue after evaporation. This is 0.03 g per 0.10 dm³, equivalent to 0.30 g/dm³.
A clear-looking sample may still contain dissolved contaminants or microorganisms. Do not use appearance as a drinking-water test.
Specification references
AQA 8462 section 4.10.1.2 and required practical 8; Edexcel 1CH0 Issue 4 section 2.12. Both tiers. The boards name different treatment methods.
Copy these details if you'd like to report a problem. Your answers and history aren't included. Nothing is sent automatically.
Write an explanation
A water sample looks clear and has very little residue after evaporation. Does this show that it is potable?
Compare your explanation with the points below. The text you type isn't marked, saved or sent anywhere.
Compare with the example
Check your explanation for
Distinguish dissolved residue from microbes.
Explain what potable means.
State a limitation of appearance and residue data.
Example answer
The tests show little non-volatile residue and no visible particles. They give no direct evidence about pathogens or some harmful dissolved chemicals, so they do not establish potability.
An answer to improve
Clear water with a low residue mass is always safe to drink.
Improve your answer
Use the observations and scientific principles to improve your explanation.
Save your progress
Your progress stays in this browser. Turn on saving if you want to keep it when you leave the page.