The treatment processor directly depend on the impurities present in the water for removing various types of impurities the following treatment processes are used
| Impurity | Process used for removal |
|---|---|
| Floating matters as leaves, dead animals etc. | Screening |
| Suspended impurities as silt, clay, sand etc. | Plain sedimentation |
| Micro-organism and colloidal matters | filtration |
| Dissolved gases, tastes and odours | Aeration and chemical treatment |
| Hardness | Water softening |
| Pathogenic bacteria. | Disinfection |
The character and degree of treatment will directly depend upon the nature of water or indirectly on the source.
The water of surface source generally contains a large number of impurities, therefore, they will require all the treatment stated above.
Sometimes, the water of takes or impounding reservoirs are free from suspended matter, therefore it will require filtration and disinfection only ground waters, which are usually clear, may require filtration and disinfection and chemical treatment for the removal at pathogens, iron removal, softening etc.
Sometimes, groundwater contains dissolved hydrogen sulphide which gives very bad odour and requires its removal.