Plumbing: Basic Systems

a water-supply system

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.

drain/waste-vent (DWV) system

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.

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

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

Faucet shutoff: Separate valves control the hot and cold water.

Want to learn more about plumbing? Visit our plumbing library.

Got a wet basement? Visit our site dedicated to Basement Waterproofing.

Advanced Plumbing: Pro Tips and Simple Steps (Stanley Complete Projects Made Easy) (Paperback)

Advanced Plumbing: Pro Tips and Simple Steps

Book Description
Kitchen and bath remodels are among the most popular home improvements. But plumbing can be intimidating. Advanced Plumbing builds confidence and expands capabilities with comprehensive, easy-to-follow instructions.

A one-stop guide to changing or adding plumbing for beginning and intermediate do-it-yourselfers:

  • Plumbing skills needed for every project
  • Detailed photos of each step
  • Tips and shortcuts

Prestart checklists provide at-a-glance information:

  • The right tools
  • Complete materials
  • Estimated time needed

This book simplifies complex plumbing projects, from planning to cleanup:

  • Adding new supply lines
  • Installing drain-waste-vent pipes
  • Connecting plumbed appliance


Plumbing 1-2-3 Book

Plumbing 1-2-3 Book

This book from The Home Depot covers plumbing installation, maintenance, repair, troubleshooting and more.

Top of Page Prev:   Next related page, article or category

Water Supply


Last modified: Friday, 2007-11-02 21:59 PST