An expert guide about how home water supply systems work, with information and detailed diagrams that explain how water is distributed through your home.

How Water Gets to Your House

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.

Diagram showing the main water meter and shutoff valve for a home.
The main water shutoff valve and water meter are usually located in an underground box near the street.

Reading a Water Meter

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

Diagram of 2 types of water meter display, including six dial, digital-readout, and its indicators.
Water Meter Dial Displays © HomeTips

Water Shutoff Valves

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.

How Water Moves Inside Your House

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.

Diagram of the supply and drain waste vent systems in a home.
Diagram of the water supply and drain waste vent systems in a home. © Don Vandervort, HomeTips

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.

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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” and served as MSN’s home expert for several years. Don founded HomeTips in 1996. Read more about Don Vandervort