What causes a knocking in the pipe when the cold water tap is switched on?

Answer:
Pipe isn't properly fastened to keep it from knocking. An anti-hammer arrester installed in cold water line should help eliminate knocking. The knocking caused by sudden burst of water pressure in line when a valve or faucet is opened.
First answer by My442. Last edit by My442. Contributor trust: 11 [recommend contributor recommended]. Question popularity: 0 [recommend question].