Serial No | NSF WQI | Description of quality (1978) | Class by CPCB | Remarks |
1 | 63 - 100 | Good to excellent | A | Non polluted |
2 | 50 - 63 | Medium to good | B | Non polluted |
3 | 38 - 50 | Bad | C | Polluted |
4 | 38 & less | Bad to very bad | D, E | Heavily polluted |