A water meter is the device a utility uses to measure how much water a home uses. Most home meters are positive-displacement types that fill and empty a fixed chamber, like a nutating disc or oscillating piston. A dial called the register shows the total. You can also use it to spot leaks.
A water meter is the device that measures how much water your home uses. The water utility owns it and reads it to bill you. It usually sits in a box near the street, held in place by a meter yoke. This page is about the meter itself, not the bill.
How a water meter measures use
Most home meters are positive displacement meters. They measure water by filling and emptying a fixed-size chamber over and over. A nutating disc meter is a common home design. A disc inside wobbles as water passes through. PNNL says the flow "causes the disk to nutate, or wobble, on its axis." An oscillating piston meter works much the same way, using a piston that spins in a round chamber. Each wobble or spin equals a set amount of water.
Larger buildings often use velocity meters instead. A multi-jet meter aims jets of water at a small spinning wheel. A turbine meter spins a wheel right in the flow. The faster the water moves, the faster the wheel turns.
The register and finding leaks
Every meter has a register. This is the dial or display that turns the inside motion into a number you can read. Positive displacement meters are very accurate at low flow. That low-flow accuracy is what lets a meter catch a small, steady leak.
You can use the meter to check for a hidden leak. Turn off every faucet and fixture in the house. Then watch the register. If it keeps moving, water is escaping somewhere it should not. For the full method, see how to do a water meter leak test. To make sense of the numbers on your statement, see how to read your Phoenix water and sewer bill.