Three water samples namely river water, untreated sewage water and secondary effluent discharge from a sewage treatment plant were 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, having BOD 20mg/l, is secondary effluent discharged from a sewage treatment plant.
SampleB, having BOD 8mg/l, is river water.
Sample C, having BOD 400mg/l, is untreated sewage water.