Plumbing: Basic Systems

We tend to take our plumbing for granted -- until something clogs or starts leaking on a Saturday afternoon. That's when a little plumbing know-how pays off, both in dollars saved and convenience gained.

Your home’s plumbing consists of two basic systems: a water-supply system and a drain/waste-vent (DWV) system. In the water-supply system, the water usually enters the house through a main service pipe and meter, unless you have a private well. Pressure, supplied by gravity from a local water tower or from a well pump, pushes the water through the system. Parallel supply lines carry hot and cold water to fixtures and appliances.

The DWV system is a separate set of non-pressurized pipes that carry water, waste and gases out of the house. Because the force of gravity carries off the waste, the horizontal drain pipes slope. Each main horizontal section of drain should contain cleanout plugs for removing blockages. At each fixture, the drainpipe contains a U-shaped trap, also called a P-trap, that traps water in its curve to create a seal that prevents sewer gas from escaping into the house. A toilet has a built-in P-trap.

The vent system (image below), connected to the drainage system, allows sewer gases to escape, improves drainage, keeps P-trap seals in place and prevents water from backing up between fixtures.

Emergency Shutoff Valves

Shutoff valves allow you to control water flow to all or parts of the water-supply system to reduce damage from a supply leak or to make repairs or replace fixtures. The main shutoff, whether indoors or outdoors, is generally near where the service line enters the house, usually next to the meter. On a private system, it will be near where the line leaves the pressure tank. You’ll also find shutoff valves at the water heater, boiler, individual fixtures and outdoor water lines.

Above: Main shutoff: This valve controls the flow of all water entering the water-supply system.

Above: Toilet shutoff: This valve is usually on the cold-water supply located underneath the tank.

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