Pollution index (mg/L)

Water quality classification

I

II

III

IV

V

DO^a

≥7.5

≥6

≥5

≥3

≥2

VP^b

≤0.002

≤0.002

≤0.005

≤0.01

≤0.1

COD mn^c

≤2

≤4

≤6

≤10

≤15

NH3-N^d

≤0.15

≤0.5

≤1.0

≤1.5

≤2.0

Expected output

0.1

0.3

0.5

0.7

0.9