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