An expert guide about how home water supply systems work, with information and detailed diagrams that explain how water is distributed through your home.
The water company delivers the water through a main supply pipe, which is typically 1 inch in diameter or larger. (A pipe is measured by its inside dimension, so a 1-inch copper pipe is about 1 1/8 inches in outside diameter.)
Read more: Types of Pipes
In most cases, the pipe runs through at least one main shutoff valve, located outside the house in a “Buffalo box” (an underground utility box that houses an access point to the main water line). It is usually buried in the yard near the house or just inside the basement or crawlspace.
For single-family homes, it is most commonly located in front of the house, near the street. In regions with very cold winters, it may be inside the basement or crawlspace; it’s often placed where the meter reader can check it monthly without disturbing you.
The water company uses a water meter also housed in this box to measure how much water you use (unless your water use isn’t tracked). Dials or a digital readout on the meter record how many cubic feet of water flow to your house.
The company meter reader records the numbers each month, and the company computes the difference between last month’s and this month’s readings to calculate your bill. Reading a digital meter is easy, just like reading a car’s odometer. To read a dial-type meter, record the smallest of the two numbers near the tip of each needle.
Read more: How to Read Your Water Meter
A main shutoff valve is often located on each side of the water meter. The one on the street side is the water company’s valve, the one used to shut off the system when the company wants to work on or change your meter.
The other one controls water that flows to your house. This is your main shutoff; turning it completely clockwise will stop all water flowing through your water supply system, both indoors and outdoors.
A gate valve, used as the main shutoff valve, is designed to be used either completely open or closed. As you open the valve, a tapered wedge retracts from the water channel into the valve’s body, allowing water to flow. When closed, the wedge creates a seal.
Other valves control the flow of water through parts of your supply system. A valve near the house may shut off all water indoors; another may control all garden water.
The main supply line usually runs to the water heater, where it divides into cold and hot water pipes. From there, supply pipes almost always travel in pairs, hot and cold. Pipes from the water heater are typically 3/4 inch but may be 1/2 inch. Horizontal pairs run below walls and then vertical pairs, called risers, run up to the various rooms.
In newer homes, there are separate lines running from the water heater to each room, so water use in one area does not affect use in another area. In an older home, a single line may loop throughout the house, meaning, for instance, that if someone flushes a toilet downstairs the cold water supplying a shower upstairs will have lessened pressure, causing the shower water to suddenly become hot.
• Home Plumbing Systems Overview
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