Every home has 3 basic types of plumbing systems: supply lines, fixtures, and drains.
Although it may appear a random puzzle of pipes and fittings, the system and its various components work together in a logical way.
- 1. The Supply Line System
- 2. The Plumbing Fixtures System
- 3. The Drain-Waste-Vent (DWV) System
- Related Resources
- Final Thoughts
- Call 1-Tom-Plumber
1. The Supply Line System
The first type of plumbing system is the water supply line. The supply line system is made up of pipes, fittings, and valves that carry potable (or drinking) water throughout the house. Water enters your property from a reservoir, municipal water system, or, in rural areas, from a private well.
How Does Water Get to You?
Typically, the water passes through a curb valve near the street. This portion of the supply system is owned by the city. It then enters into a water meter and main shutoff valve usually located on the street-side of your house in a basement or crawl space.
If your house is built on a slab (no basement or crawl space), the water meter and shutoff valve should be found in a utility room or closet.
Potable Water Travels by Water Pressure
Water pressure is what pushes water to where it needs to go. But the pressure needs to be just right for it not to cause leaks or burst pipes.
Water pressure in the supply lines ranges in normal conditions ranges from 35-75 pounds per square inch (PSI). Ideally, it is between 40 and 60 PSI (50 PSI is perfect for most households). Pressure that is less than ideal can cause insufficient water flow from your fixtures. Higher water pressure can cause water hammer or burst pipes, leading to severe water damage.
Cold & Hot Water Runs
From the cold water main line one supply pipe branches off to the water heater to begin a second, parallel run of pipe called the hot water main.
From there, secondary branches of hot and cold water, usually spaced about 6 inches apart, snake through the walls and ceilings to your fixtures.
In a well-designed system, each branch contains its own shutoff valve near the point where it leaves the main line. This allows you to turn off the water to a fixture (like your kitchen faucet or toilet) without cutting off water from the rest of the house.
2. The Plumbing Fixtures System
Fixtures are the second of three types of plumbing systems in your home. It includes sinks, bathtubs, showers, toilets, sprinkler systems, and water-using appliances like dishwashers and clothes washers.
These fixtures connect either temporarily or permanently to the supply line and drainage systems. Not all fixtures need both. For example, a toilet tank has a cold water line only while a dishwasher uses only the hot water line.]
What are Air Chambers?
Behind the wall at most fixtures are air chambers. These are capped vertical pipes that trap a column of air to cushion onrushing water when the faucet is turned off.
Without an air chamber, an abrupt turn-off might create several hundred pounds of pressure within the water supply system. This could result in water hammer, a problem that can burst open pipes and fittings.
3. The Drain-Waste-Vent (DWV) System
The drain system is the third basic type of plumbing system. It is often called the DWV (drain-waste-vent) system, and it is the least visible part of the entire home plumbing system. For good reason, it’s also the most strictly regulated by housing and plumbing codes.
Wastewater Travels by Gravity
Unlike the water supply system, the drain system is not under pressure. It relies on gravity to carry wastewater out of the house.
P-Traps Are Your Friend
Each fixture is connected to a drainpipe by a P- or S-trap (while you can still find S-traps in older homes, they are now considered illegal according to the U.S. Uniform Plumbing Code).
Each trap is filled with water to prevent sewer gas from entering your home. Wastewater can go out, but due to the “water trap,” small animals and sewer gas can’t get in. Every time a toilet is flushed, or a sink is emptied, the water in the trap is replaced.
Stacks & Venting
Branch drains lead to a larger vertical pipe called a stack. This is possibly the most important piece of plumbing in your home.
The bottom of the vertical stack is at the same level as the outgoing sewer line. The stack goes all the way up, through the roof, to vent sewer gas and maintain atmospheric pressure in the system. A larger home might have multiple stacks.
At ground level, or below if there is a basement, the stack makes a near-45-degree turn to become the horizontal main sewer drain. It slopes away from the house (this downward slope takes advantage of gravity to move the wastewater) and enters a public sewer line or private septic system.
- Water hammer: how to fix your noisy pipes
- Pipes making noise? Here’s what the difference sounds mean
- Water pressure: How to test it at home (with video)
- Where is my main water shut off valve?
- What is a P-trap?
- Plumbing Safety Tips
The plumbing system in your home seems complex. We get it. I mean, that’s why we’re in business after all. Not everyone understands it or wants to work on it when needed.
However, a basic knowledge of the three types of plumbing systems in your home will help you understand if you’re being taken care of (or taken advantage of) by your plumber. It can also lead to you being able to handle some projects on your own, which can save money and bring you satisfaction for a job well done.
1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.