Three water samples namely river water, untreated sewage water and subjected to BOD test. The samples were labelled A, B and C but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/L and 400 mg/L respectively, which sample of the water is most polluted ? Can you assign the correct label to each assuming the river water is relatively clean?

Explanation

Sample A - Second influent
Sample B - River water Sample
C - Sewage without treatment