What Water Shutoff Valves Do. Water shutoff valves are fittings used in plumbing, which can control anything from individual fixtures such as faucets and toilets, to your home's entire water system.

A gate valve will have a screw knob that you can turn to shut off the water; ... If your plumbing is all on one level, try the tub faucet and the outside faucet if the weather allows.