Potable water is that which is safe to drink, pleasant to taste and can be used for domestic purposes. Contaminated water is that which contains bacteria that cause diseases. Polluted water is that which contains substances that are undesirable or unsuitable for drinking or domestic use.
Drinking water should be free of:
- disease-causing organism or harmful bacteria or micro-organism in the form of colloidal matter
- all kinds of dissolved toxic chemicals
- Hazardous gases – but may contain a good amount of dissolved oxygen
- dissolved minerals that give water extreme hardness, and should not accumulate sediment when standing
Drinking water should not contain a sufficient amount of suspended matter. It should be as far as possible colourless, odourless, cool and pleasant to taste.
The suitability of water for a particular purpose can be determined only after a thorough analysis and investigation of the source or origin or supply.
A complete water analysis consists of four sections:
Bacteriological and physical analysis is of prime importance for the supply of drinking water.
To check the quality of potable water, the following simple tests will be helpful for its physical analysis:
Testing to check the quality of drinking water
Presence of organic impurities or contamination from sewage
Add four drops of potassium permanganate solution to a small glass of water and stir well. If the sample is pure, it will appear purple or red. It will turn pale or yellow if any organic impurities are present. Potassium permanganate can also be mixed in crystal form.
presence of lead
Add six drops of sulfuric acid to a small glass of water. If a white precipitate is formed, it is an indication of the presence of lead.
Another way to know the presence of lead is as follows.
Add a drop of ammonium sulfide to a small glass of water and stir it well. The black color of the precipitate would indicate the presence of lead.
presence of zinc or iron
Add a few drops of ferro-cyanide of potassium to a small glass of water and stir it well. If the water turns green then it is zinc and if the water turns blue then iron is present.
presence of copper
Add eight drops of ammonia to a small glass of water. If the water turns blue in color then copper is present.
presence of carbonic acid
Add a lemon to a sample of water and stir it well until it turns milky. If this turbidity disappears when hydrochloric acid is added, it is a sign of the presence of carbonic acid.
A clear and sparkling water not necessarily suitable for human consumption