Meters matter––but are they accurate?

Water meters really are fairly simple and have changed little over the years. The vast majority of the Las Virgenes Municipal Water District’s (LVMWD) nearly 19,000 residential service use positive displacement, disc meters.

Here’s how they work

Meters are made up of two totally enclosed, cast metal parts: a chamber and a register. Since each part is separately sealed, they interact by use of magnets.

When you open the meter box at your property, it’s the register you will be looking at. You can flip up the meter lid, and you’ll see the numbers and dials of the register.

The lower portion of the meter is called the chamber. Water flows from the district lines in the street, through a service line, and into the chamber. The force of the water as it passes through the chamber causes an internal disc to "nod" up and down. It "nods" slowly for low flow and at increasingly faster speeds for higher flows. This motion causes a circular magnet at the top of the chamber to spin.

This spinning magnet transfers a magnetic energy through the top wall of the chamber and through the bottom wall of the register just above, causing a second round magnet at the base of the register to spin. The register magnet then engages gears within the register, which turn the register needle and numbers.

Are meters accurate?

Meter manufacturers are required to calibrate and test every meter before it leaves the factory. The water district receives written certification with each meter, verifying it has tested at least 99 percent accurate for separate low, medium and high flow tests.

As meters age they tend to slow down. Over time the disc and the chamber wear, and there’s more of a gap between their surfaces, allowing water to get by without causing the disc to move.

For this reason, older meters end to read lower than actual water flow. LVMWD confirms this, with tests each year run on hundreds of meters are replaced. Each one is tested for high, medium and low-flow accuracy, and the consistent findings show they record less than actual use.

A meter replacement program is an important part of LVMWD’s service maintenance to ensure accurate water bills.