Which of the following is purification of water at large scale - a) Disinfection of well b) Rapid sand filterc) Slow sand filterd) Household purification

Purification of water Purification of water is of great importance in community. The method of treatment to be employed depends upon the nature of raw water, and the desired standards of water quality. For example ground water (deep well, tube well and springs) may need no treatment. On the other hand surface water (river) requires extensive treatment. Purification of water may be : - Purification on large scale Storage Filtration Slow sand (Biological filter) Rapid sand (mechanical filter)       3. Disinfection Chlorination Ozonation UV irradiation Purification on small scale Household purification Boiling Chemical disinfection        2. Disinfection of wells