Value of FBI

Water quality

Degree of organic pollution

0.00 à 3.75

Excellent

Without organic pollution

3.76 à 4.25

Very good

Slight organic pollution

4.26 à 5.00

Good

Probable organic pollution

5.01 à 5.75

Average

Substantially organic pollution

5.76 à 6.50

Rather bad

Substantial organic pollution

6.51 à 7.25

Bad

Very substantial organic pollution

7.26 à 10.00

Very bad

Serious organic pollution