People turn off the flow of water from a main line to secondary pipes throughout a house when dealing with various situations. Sometimes the situation involves a natural disaster such as a winter freeze or earthquake, or human actions such as construction or underground drilling, that result in a damaged, leaky or broken pipe. Other situations include installation of a new appliance that relies on water, such as a whole house dehumidifier or sprinkler system or vacation preparation.
Shut off any appliances in the house that relies on a continuous flow of water such as a boiler, hot water heater or whole-house humidifier. Follow any shutdown instructions provided in the owner's manual for each appliance.
Determine the location of the main water supply line (pipe) and the type of shut-off system. If you have a well, check for the line near the pressure tank. The pipe may have handle attached to a ball valve or a wheel attached to a gate valve. If it doesn't, check for a circuit switch marked "well pump" in a main or secondary circuit breaker box inside the home. If you have municipal water, check for a handle or wheel on a pipe in the basement, under the sink, in a closet under the floor or in the garage (if applicable). In addition, check near the water meter, on a pipe coming out of the ground and connecting with another pipe on the side or crawlspace of the house, or on a pipe under a circular or square access panel in the backyard or nearby street.
Turn the water off. If you have a valve system, put on your grip-style gloves. Turn the handle a quarter turn right (ball valve) or the wheel right until it can no longer turn (gate valve). In the case of wells that don't use a shut-off valve, turn off the electricity going to the well pump by opening the circuit breaker box and flipping the "well pump" circuit switch.