Which of the following statements is correct?

a- Surface water available from rivers, canals, lakes, etc. is always pure.
b-  Human beings pollute the water through industrial, agricultural and cultural activities.

Only statement b is correct.

Indiscriminate use of water by increasing population and industrial expansion has led degradation of the quality of water considerably. Surface water available from rivers, canals, lakes, etc. is never pure. It contains small quantities of suspended particles, organic and inorganic substances. Human beings pollute the water through industrial, agricultural and cultural activities.