Whole-house shutoff. Knowing where and how to shut off water for the entire house is prudent for every member of the household to know. The most important valve in the house is the main shut-off valve for the entire plumbing system. This valve, generally located near the foundation (inside or outside), in the basement or in the garage. Standard practice has changed over the years and it depends on the layout of the house. In some cases just locating this valve can be a chore. If you can not find the valve or if it is inoperable your should have your plumber install one or replace the valve.
For water service leaks (the piping between your house and the water meter), the only way to shut this off is at the valve on the street side of the water meter. This require a water meter key, which can be picked up at the hardware store.
Whole-house hot-water shutoff. There should be a valve on the cold-water inlet into your water heater. This controls all of the hot water to the house. If there isn’t one on yours, you or your plumber should install one.
Toilet shutoff. Look for this shutoff, typically with an oval handle and under the left side of the toilet tank.
Sink shutoffs. These shutoffs usually sit just beneath the sink or within the cabinet or vanity under the sink. The one on the left is usually for the hot water, the one on the right for cold water.
Dishwasher shutoff. Look first under the kitchen sink. Not there? If you have an unfinished basement, look between the ceiling joists just below the appliance.
Icemaker shutoff. Look first under the kitchen sink. Not there? If you have an unfinished basement, look between the ceiling joists just below the appliance. Possibly, someone hooked up in the crawlspace.
Clothes washer. There should be valves where the house-supply lines meet the washer hoses. Washer hoses are notoriously weak, so always close the valves when leaving home for an extended period.