There are two main types of plumbing that serve a house: drain-waste vent pipes and water supply pipes. The water supply pipes work under pressure while the drain-waste vent pipes work by gravity. Natural gas piping, central vacuum systems and other specialized plumbing systems are also available.

Water Supply Pipes

The main water supply pipe connects to either the main of your water company or to a well on you property. This water supplies water to your home. You’re familiar with the pressure that moves water through a fire hydrant if you’ve ever seen it.

Once water has reached your home, it is split into two systems: one for cold water, and another that connects to the heater. The pipes for hot and cold water are often connected.

Gravity is used to drain waste into the sewer. A soil stack is a vertical run 3 to 4 inches long of pipe that carries waste to the main drain. This drain empties into a sewer or septic tanks.

Vent pipes keep sewer gases out of your home, and traps–water-filled bends within pipes–keep them from escaping down the drain. Vent pipes can connect to the soil stacks, or vent directly through your roof.

Different types of pipes

All plumbing systems share one thing in common: pipes. Pipes are the foundation of home plumbing.

The size and material of a pipe can be a good indicator of its purpose. White plastic, copper and galvanized (silver toned) pipes between 1/2 and 1 inch in diameter carry water. However, some galvanized, black, and flexible copper pipes with the same dimensions may carry gas.

For drain-waste vent system, large-diameter (1.5 inches or more) cast-iron, black, and copper pipes are used. Cast-iron or plastic pipes of 4 inches or greater are used to serve the main soil stack, which is the waste and vent line for toilets and other fixtures.

Pipes with a diameter of 1 1/2 inches or more are used to vent other waste. Light-gauge pipe measuring 1 1/4 to 1 1/2 inches in diameter can be used for vacuum-cleaning systems.

Flexible copper tubing or plastic tubing with a smaller diameter is used to supply water supplies for hot water dispensers, ice makers, water filters and other water-related equipment. Brass or plastic fittings are available. Flexible (sometimes ribbed), pipes can also be found. These range from small wall valves to toilets and faucets to flexible piping that is rated to deliver gas from valves to water heaters and dryers.

A variety of fittings can be used to join metal or plastic pipes. They can be used to connect to any type of fixture, turn corners, branch off in two directions, reduce the size of the pipe, or increase its length.

Here’s a closer look at some of the most popular types of pipes.

Rigid Copper Pipe

For water supply piping, rigid copper pipe is a popular choice. It is strong and durable and resists mineral buildup. It can also handle hot and cold water.

Hard supply pipe comes in three thicknesses: L (medium wall thickness), M (thin wall thickness), and K (thick walls). Type M is the most common type of above-ground plumbing.

Soft Copper Pipe

Although soft copper pipe is more costly than hard copper, it is still flexible enough to be routed without as many fittings. Type L is used more often than Type M in above-ground applications.

Both types of copper pipes can be joined using either permanently soldered fittings, or flare/compression fittings which can be disassembled.

Galvanized Steel Pipe

Before 1960, galvanized steel fittings and pipe were standard in water supply plumbing. They are still very common. Although the galvanized zinc coating protects against corrosion and rust, the insides of the pipes can become clogged with mineral deposits over time and eventually corrode.

Threaded fittings are used to make watertight connections. Vent plumbing is possible in certain houses with larger diameters of galvanized steel pipe.

A dielectric union should always be used wherever copper is connected to steel pipes in order to prevent corrosion due to electrolysis. Although black iron pipe looks similar to galvanized Steel, it is not resistant to corrosion and is used for gas lines in homes.