A potable water is one that is safe to drink, pleasant to taste and usable for domestic purposes. Contaminated water is one that contains the bacteria which causes diseases. Polluted water is one that contains substances which are undesirable or unfit for drinking or domestic use.
Drinking water must be free from:
Disease producing organisms or harmful bacteria or micro organisms as colloidal matter
Dissolved poisonous chemical substances of all kinds
Objectionable gases – but may contain good amount of dissolved oxygen
Dissolved minerals which impart excessive hardness to water, and must not deposit sediment on standing
Drinking water should not contain any appreciable amount of suspended matter. It should as far as possible, be colourless, odourless, cool and pleasant to the taste.
The suitability of water for any particular purpose can be determined only after a complete analysis and investigation of the source or origin or supply.
A complete water analysis consists of four sections:
For drinking water supplies the bacteriological and physical analysis are of prime importance.
The following simple tests will be helpful for physical analysis of potable water to check its quality
Tests to Check Quality of Drinking Water
Presence of Organic Impurities or Contamination from Sewage
Add four drops of a solution of potassium permanganate to a small glass of water and shake it well. If the sample is pure it will appear purple or red. If any organic impurities are present it will turn yellow or pale. Potassium permanganate can also be added in crystal form.
Presence of Lead
Add six drops of sulphuric acid in a small glass of water. If white precipitate is formed then it is an indication of presence of lead.
Another way to know the presence of lead is as follows.
Add one drop of ammonium sulphide in a small glass of water and stir it well. A black discolouration of the precipitate will indicate the presence of lead.
Presence of Zinc or Iron
Add few drops of Ferro-cyanide of potassium to a small glass of water and stir it well. If the colour of water turns into green then zinc is present and if colour of water turns into blue then iron is present.
Presence of Copper
Add eight drops of ammonia in a small glass of water. If the colour of water turns into blue then copper is present.
Presence of Carbonic Acid
Add lime in a sample of water and shake it well until it turns milky. If this turbidity will disappear on the addition of hydrochloric acid, then it is an indication of presence of carbonic acid.
A clear and sparkling water is not necessarily fit for human consumption