i) Take 10ml of distilled water and 10ml of hard water (from hand pump) in separate test tubes.
ii) Add a couple of drops of soap solution to both.
iii) Shake the test tubes vigorously for an equal period of time and observe the foam formed.
iv) The test tube containing distilled water shows more foam. This is because the whole of soap is available to form foam.
v) The test tube containing hand-pump water may show a white curdy precipitate. This indicates that water is hard water.
vi) Hard water contains soluble salts of calcium or magnesium. This is because calcium and Magnesium ions form precipitate with soap, thus wasting some of the soap.