Heavy metal pollution of water is caused by:

Heavy metals (cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, zinc, molybdenum, tin) are among the main pollutants. Industrial paints are loaded with metals such as lead, calcium, cadmium and other such chemicals. When any amount of paint is led off into the water bodies it causes water pollution by causing the amount of heavy metals present in water to fluctuate. Each one of these has severe toxic effects on living beings, and tend to accumulate in aquatic food chains.