Mesa Water or IRWD: Which Utility Serves Your Costa Mesa Home, and Who Fixes a Meter Leak

The two water utilities in Costa Mesa

Mesa Water describes its service area as about 18 square miles and roughly 110,000 residents, including John Wayne Airport. If you moved recently and have not received a bill yet, the previous owner or your property manager can tell you.

How to confirm your provider

1. Check the bill. The utility's name is printed on every water bill.
2. Look at the meter box lid. Many lids carry the utility's name or logo.
3. Ask the utility. Call either utility with your address and they will confirm.

For condos and apartments, the building may have a master meter. In that case the association or owner is the customer, and you would call them first.

Where the utility's pipe ends and yours begins

The water main in the street, the service line to the meter, the meter itself and the utility's valve in the meter box are the utility's equipment. Leaks there are theirs to fix.

On the house side of the meter, the service line that runs to your house, the house shutoff valve and all the plumbing inside are generally the property owner's. Each utility sets its own exact rules, so confirm the handoff point with yours if a leak is right at the meter.

The valve inside the meter box belongs to the utility. In a true emergency you may need to use it, but tell the utility if you do.

Whose leak is it?

Where the water shows up points to who should respond.

The ten-minute meter test

Use the meter to confirm a leak and narrow down where it is.

1. Turn off all water use. Taps, toilets, appliances, sprinklers and any softener.
2. Watch the leak indicator. The small triangle or dial on the meter face should be still.
3. Close the house shutoff. If the indicator keeps moving, the leak is between the meter and the house.
4. Open it again. If the indicator only moved with the house valve open, the leak is inside.

A leak between the meter and the house is covered on our water line repair page. A leak inside the house is a job for leak detection.

What else differs between the two utilities

Water quality reports are separate. Mesa Water's 2025 report lists 2024 groundwater hardness at an average of 6.4 grains per gallon, with a range from 1.2 to 14. IRWD publishes its own figures, which differ. If you are deciding on a softener or filter, read the report for your actual provider.

Programs differ too. Rebates, conservation rules and backflow testing notices come from your own utility. Mesa Water, for example, requires annual testing of backflow prevention assemblies, and protection inside the building follows the California Plumbing Code, which is based on the Uniform Plumbing Code (UPC).

If you are unsure whether you need a softener at all, our water softener page starts with a hardness test at your tap.

High bill, no visible leak

A sudden jump on the water bill is the most common reason people check which utility they have. Before calling anyone, rule out the easy causes: a toilet that runs between flushes, an irrigation timer that changed, a softener stuck in regeneration, or a hose left dripping into a planter.

If none of those explain it, run the meter test above. A moving indicator with everything off means water is escaping somewhere, and the test with the house valve closed tells you whether it is in the buried service line or inside the house.

Some utilities review high bills caused by a leak once it has been repaired. Ask yours what it requires, and keep the repair invoice.

Irrigation deserves its own look. A cracked sprinkler line or a valve that never fully closes can lose a lot of water without any sign indoors, and the only clue is often a patch of lawn that stays green and soft. Turning the irrigation off at its own valve and repeating the meter test tells you quickly whether the sprinklers are the source.

Water utility questions