Your Plumbing System

With so many pipes and fittings running unseen inside walls and floors, a plumbing system can seem complicated and mysterious. But plumbing is actually a straightforward matter of distributing incoming water to where it's wanted and facilitating the outflow of waste. Here's an overview of how household plumbing works.

Step-by-Step
Supply, Drain, and Vent systems

1. The supply system brings water into your house, divides it into hot and cold water lines, and distributes it to various fixtures (sinks, toilets, showers, tubs) and appliances (washing machines, dishwashers, water heaters, heating system boilers).
2. The drain system carries water away from the fixtures and appliances, and out of the house.
3. The vent system supplies air to the drain pipes so waste flows out freely. Because drains and vents use the same types of pipes and are tied together, they often are referred to as the drain-waste-vent system, or DWV.

Locating the Water Meter and Main Shutoffs

The first step toward gaining mastery over your house's plumbing system is to locate the water meter and, more important, the main shutoff.

Look for the place where water first enters your house. Usually, you'll find a pipe an inch or so thick, called a water main, coming up through the floor in your basement or first floor. If you have metered water, the pipe will enter and exit a round gauge, the water meter. This has either a digital readout that looks like a car's odometer or a series of five or six dials. The meter tells how much water passes into the house. If you have a well, or if your bill does not change no matter how much water you use, you don't have a meter.

Near the place where the water main enters your house, look for one or two valves that you can turn on and off by hand. This is the main shutoff for the house. You may have an additional shutoff outside the house, buried in a cavity sometimes called a "buffalo box." To find it, look for a round metal cover in the ground near the street or the edge of your property. It may be overgrown with grass. Pry it up and look inside with a flashlight. There may be a valve that you can turn by hand, or you may need a special long-handled "key." Older homes in warm weather locations sometimes have an exposed valve just outside the house.

If you have an older home, don't depend entirely on the inside shutoff; it can break, leak, or stop shutting off completely. If you'll have to shut down the system often during a project, learn where your outside shutoff is and use it to shut off the water.

Where your responsibility ends.

The curb box is the continental divide when it comes to assigning responsibility for plumbing repairs. The plumbing from the curb box to the main is the responsibility of the water company. Anything on the house side of the curb box is your responsibility. However, if you will be adding new fixtures (not just replacing old ones), your municipality may require a larger water main coming into the house. Check when you get your permit.