Plumbing 101


n1: The pipes, fixtures, and other apparatus of a water, gas, or sewage system in a building. n2: The work or trade of a plumber.

Plumbing Intro
Basic Principles
The Water Meter & Main Shutoff
Main Water Supply Pipe
Water Pressure
Supply Pipes & Fittings


After the construction workers completed the outside of your home, another group of contractors installed several important mechanical systems running inside the walls and below the floors. Though these systems are largely invisible, they are crucial to a properly functioning house.

The first of these systems to be installed was the plumbing. Behind the visible fixtures you see today-such as tubs, sinks and faucets-lays a hidden network of pressurized water supply pipes and gravity-assisted drain pipes. You may be able to see some parts of this network exposed in basements and utility rooms, but for the most part the plumbing system does its crucial work unnoticed.

If you're lucky, you rarely need to worry about your plumbing. Your toilet flushes and your sink drains smoothly; you have plenty of hot water and your shower has good water pressure.

But luck doesn't last forever. Many problems can occur in this system. Pipes can break, drains can plug, valves can leak. When trouble arises, it's helpful if you know how the system works. And it's very important that the system work properly, both for convenience and your family's health.

Basic Principles

The basics of a plumbing system are easy to understand. Water enters you house through a pressurized water line. After being split into hot and cold water lines, the water supply runs to each fixture in your home. Once used, fresh water becomes waste water, and it enters the drain-waste-vent (DWV) system. Gravity now takes over, pulling the waste water down a series of sloped, ever larger pipes toward the house sewer.

Water arrives under pressure; water leaves by gravity, taking with it dish soap, human waste and anything else put down the drain. It's a simple and elegant system. Until something goes wrong. Ironically, the same principles that allow your system to operate smoothly are what cause many of the problems. Under the stress of constant pressure, supply pipes corrode and eventually leak or burst. And the slow movement of waste through the DWV pipes can lead to clogs.

Throughout this Plumbing 101, you'll learn more about plumbing fundamentals which will make it possible for you to follow the flow of water through your house. You'll also learn to identify parts of the system that could give you trouble in the future. While every house relies on the same plumbing principles-pressure in, gravity out-plumbing materials vary widely from house to house. Many systems are amalgams of different materials-especially in older homes, where repairs and updates may have been done in several phases. Identifying these materials and knowing their characteristics will help you when troubles eventually arise.

The Water Meter & Main Shut-off

Start your tour of the plumbing system with the main water supply shutoff valve. If a pipe bursts or another plumbing emergency arises, you'll need to locate this valve quickly in order to stop the water flow and keep water from damaging your house.

About 85 percent of all homes receive their water from a municipal supply. If you have a municipal service, the shutoff is adjacent to the water meter, usually on the basement wall facing the street side of your house. If you don't have a basement, look in the crawl space or along the ground-floor wall next to the street.

The water meter, usually made of brass, is no larger than 6 inches in diameter. It will often have a clear top and a dial similar to your car's odometer. (Some areas now have sealed electronic meters. These allow the meter to be read off-site by utility workers.) If you have trouble finding the water meter, just follow the cold water inlet pipe from your water heater back to its source.

Most meters have shutoff valves on both sides (recently, many local plumbing codes require this). If you have a well, you'll likely find the shutoff valve located on the outlet side of your water storage tank.

Main Water Supply Pipe

While at the water meter, study the pipe leading into your house. It can give you important information about our system. If the main supply pipe leading from the street to the meter is made of steel, you could be in for a sizable repair bill in the near future. Most steel main supply pipes were installed more than 25 years ago, and are nearing the end of their life span. The cost for upgrading the main supply line from the city water main falls into your hands.

If you find that the main supply pipe is copper, you can rest a bit easier. As real estate agents will tell you, the presence of "copper-to-the-street" indicates a relatively recent installation. In addition, copper pipe lasts a good deal longer than steel. If you own a newer home in California, your line to the street will most likely be made of PVC pipe.


Fifteen percent of American households rely on private wells for their water. There are three different well designs in common use, and each design consists of three parts: The well pipe, the pump and the storage tank. Although wells are generally dependable, they can act up.

The jet pump is the most common design of a shallow well. It creates a vacuum to draw water up a well. Jet Pumps are defined as either a single-drop pipe pump or a double-drop pipe pump. The single-drop jet pump is limited to wells roughly 30 feet deep-but less at higher elevations, where air pressure drops. A double drop pump can lift water from 100 feet or more, because the surface impeller directs a portion of its water back down the second pipe (hence the term "double-drop"). The water passes through an ejector at the bottom, which creates more pressure and lift in the suction pipe. This type also needs a continuous prime to work: when the pump is turned on, the prime water is pushed through the impellers and new water is pumped up behind the prime.

For a deeper well, a submersible pump can be suspended directly in to the aquifer. The pump's electric motor is sealed and the impellers simply push water up the pipe and into your house. A submersible pump can reach very deep aquifers, and it is considered to be nearly problem-free. A submersible pump may perform without servicing for 20-25 years, but it has a major drawback: if the pump motor burns out, a truck-mounted derrick is required to retrieve it. Submersible pumps may also be used in shallow wells, but silt, sand, algae and other contaminants can shorten the pump's life.

Another type of pump, the piston pump, has rarely been in stalled since the 1950's, but many keep churning. This classic style is driven by a windmill-or by a hand-operated pitcher mechanism. The piston, submerged in the well shaft below water level, is connected to a rod that extends up the well casing.

No matter what kind of system you have the components on the output side of the pump are all similar. A well pump is not intended to run continuously and doesn't start every time you open a tap.

Your well almost certainly features a galvanized steel pressure tank, with a pressure switch, pressure gauge and drain valve attached to the tank or mounted nearby. Whenever the system is activated, water is pumped up into the tank from the ground, compressing the air in the tank. When the air pressure reaches a dermined threshold, the well pump shuts off. This air pressure provides the force needed to push the water from the tank into the fixtures. Once the water in the tank drops enough to reduce the air pressure to a predetermined level, he pump starts up again and begins to draw additional water.

Water Pressure

Normal pressure for water entering your house is 40 to 55 pounds per square inch (psi) but the pressure can be as low as 30 psi or as high as 80 psi.

Newer homes are running 65 psi entering the house. If there are fire sprinklers, they need 85 psi going into the sprinkler system and a reducer for the water line into the home.

Pressures lower than 30 psi can result in poor water flow from fixtures. Pressures higher than 60 psi could cause pipes to burst or "hammer". Hammering is when you hear the pipes rumble back and forth when water is turned on in the house. Some homes with high municipal pressure have a pressure-reducing valve near the main shutoff.? Less can be done to change low water pressure. You can, however, clean valves and replace undersized or clogged pipes. A more dramatic measure is to install a pressure-boosting pump. If you have questions about your home's water pressure, check it with a pressure gauge connected to your hose bib or have a plumber check the pressure.

Supply Pipes & Fittings

As you trace your water supply system from the main shutoff to the individual plumbing fixtures, you may notice several different types of pipes and fittings. Older houses can have a wider variety of piping, especially if the plumbing has been partially updated through the decades. Knowing what kind of piping you have is important for troubleshooting.

Your water supply system is pressurized, and the pipes must be able to withstand the pressure year after year. Water supply lines are typically steel, copper, or plastic.

Galvanized Steel was commonly used in homes until the 1960's. Now, however, it is rarely used for simple reasons: it rusts, and it's much harder to install than copper or plastic. Steel is tough, however, so it is sometimes installed where pipes are exposed and could be subject to damage. (Note: Galvanized steel pipe is also called iron pipe, while another type of piping, called black iron, is still commonly used for gas piping. The two should never be mixed. Galvanized steel will react with gas, causing zinc to flake off and plug a water heater or furnace. And if black iron pipe is used in a water supply system, it will quickly be destroyed by rust.)

Copper is considered the best choice for water supply lines, and it is also occasionally used in drain-waste-vent systems. Copper resists scale deposits better than plastic, and is much more corrosion-resistant than steel. Copper offers little resistance to water flow, which means that water pressure through copper is better than it is through a comparably sized steel pipe. Copper is light, and easy to handle and join. Copper's only drawback is that it is more expensive than other materials. This sometimes prevents budget-minded plumbing contractors from using it.

Plastic piping is used for water supply pipes in some areas, where local codes permit it. Plastic has its benefits: it is inexpensive, very easy to work with, and it doesn't corrode or rust. It also has insulating properties that minimize heat loss in hot water pipes and prevent sweating on cold water pipes.

Although plastic has gained wider acceptance in recent years, you might find that your local Building Code allows it for only certain uses, such as outdoor plumbing. In addition, a great many plumbers reject plastic water supply pipe as they feel it is inferior to copper.

Plastic water supply pipe earned its poor and somewhat unfair reputation because early generations of plastic piping used to carry hot water sometimes broke down due to the heat. Today, PVC, CPVC, and PE pipes are acceptable for cold water use, but only CPVC and PB rated at 180 degrees Fahrenheit and 100 psi, or greater, should be used for hot water lines.

One note of caution when buying a house with plastic piping: plastic is a material favored by most do-it-yourselfers. If your house has plastic piping and you suspect an amateur installed it, have it inspected by a professional to determine if the job was up to Building Code specifications.

Dielectric Fittings

If you choose to repair pipes yourself, you need to be aware that joining different pipe materials can be tricky. A trait called galvanic action can lead to premature corrosion and clogging. Galvanic action causes molecules to transfer from one type of metal to another, dramatically shortening a pipe's life span. Specialized fittings are therefore required to join pipes of different materials. And pipes must be supported with brackets and straps of the same material. In addition, pipe fittings come in a wide number of variations. Repairing a pipe can be tricky and sometimes may require some extra knowledge for your exact situation. If you're still at a loss, we suggest you ask a clerk at you local hardware store for help.

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