A water bill doesn’t get much attention until the number is wrong. But if you know what to look at, that monthly statement from EBMUD or Cal Water is one of the earliest warnings you’ll get that something in your plumbing has gone sideways. A leak you can’t see or hear usually shows up on paper first.
Here’s how to actually read the thing, and what the numbers are trying to tell you.
Start with usage, not the dollar amount
The price on a water bill bounces around for reasons that have nothing to do with leaks. Rates change, drought surcharges come and go, sewer fees get bundled in. So the dollar total is a noisy signal. What you want is the usage figure, which is the raw amount of water that ran through your meter during the billing period.
On most Bay Area bills, usage is reported in CCF, short for hundred cubic feet. One CCF is about 748 gallons. That matters because the numbers on the page look small. Going from 9 to 15 CCF doesn’t sound dramatic until you realize it’s roughly 4,500 extra gallons of water. Some statements also list gallons directly, and you may see the word “units,” which almost always means CCF.
EBMUD and Cal Water both print a usage history right on the bill, usually a little bar chart of the last several months or the past year or two. That chart is the most useful thing on the page.
Compare to the same period last year
This is the step most people skip. Comparing this month to last month can mislead you, because water use is seasonal. Summer in Pleasanton or Walnut Creek means irrigation, and your usage climbs every year when the weather turns hot. That’s normal, not a leak.
The honest comparison is this billing period against the same period a year ago. If last June you used 12 CCF and this June you’re at 28, and nothing about your household changed, that gap is worth investigating. A new baby, houseguests, a new lawn, or a hot dry stretch can all push usage up legitimately. A leak pushes it up with no explanation at all.
Look for a step change, too. A leak often shows as a usage line that was flat and then jumped and stayed high. Normal life tends to wobble. Leaks tend to plateau at a new, higher level and stay there until something gets fixed.
Use your meter as a leak test
If the bill has you suspicious, you don’t have to guess. Your water meter can confirm a leak in about an hour.
Find your meter first. In most East Bay and Tri-Valley homes it’s in a concrete or plastic box near the curb or sidewalk, under a metal or plastic lid. You may need a screwdriver to pry it up. Watch for spiders and the occasional surprise, and lift the inner cap to see the dial.
Then do this:
- Turn off every water-using thing in the house. No faucets, no dishwasher, no washing machine, no ice maker, no irrigation. If you want to isolate the house from the yard, you can shut the main valve and test in stages.
- Look at the meter. Many meters have a small triangular or star-shaped leak indicator that spins when even a trickle of water is moving. Note the exact reading.
- Wait an hour without using any water, then read it again.
If the leak indicator is spinning while everything is off, or the numbers moved during a dry hour, water is escaping somewhere. That’s a real leak, not a billing error.
Figure out where it’s hiding
Once you know water is moving, the next question is where. A few usual suspects, easiest to hardest:
Toilets. This is the number one cause of mystery usage, and it’s sneaky because it’s often silent. A worn flapper lets water seep from the tank into the bowl all day long. The classic test is a few drops of food coloring in the tank. Don’t flush, wait 15 minutes, and if color shows up in the bowl, the toilet is leaking. A single bad flapper can waste hundreds of gallons a day.
Faucets, fixtures, and the water heater. A steady drip adds up, and water heaters can leak from the tank or fittings, sometimes pooling quietly in a garage or closet. Check under sinks and around the heater for damp spots, mineral crust, or a musty smell.
Irrigation. Drip systems and sprinkler lines break underground and you’d never know unless you happened to be standing there when the zone ran. An unexplained green patch, a soggy area, or a spike that started right when you turned the system on for the season all point here.
The buried supply line. If the meter keeps creeping with the whole house and yard shut off, the leak may be in the service line that runs from the meter to your home. Older Bay Area housing stock is part of the story here. Plenty of homes still have aging galvanized steel or early copper, and our hard water is rough on pipe over the years, leaving scale and pinhole corrosion behind. A line leak can run continuously without ever surfacing.
A note for East Bay sellers
If you’re in EBMUD territory and thinking about selling, there’s a related wrinkle worth knowing. EBMUD runs a Private Sewer Lateral (PSL) program that requires many homeowners to test and, if needed, repair the sewer lateral at the point of sale and get a compliance certificate. That’s the sewer side, not the supply side your water bill measures, but both are pipes on your property that age the same way. A spike in water use and an old lateral often live in the same house.
When to call a licensed plumber
You can do all the detective work above yourself. The food coloring test, the meter test, and a year-over-year bill comparison cost nothing and tell you a lot.
Where it makes sense to bring in a pro is when the trail leads somewhere you can’t safely reach or fix. If the meter keeps moving with the house dry and you can’t find a source, if you suspect a leak in a buried supply line or inside a wall or slab, or if you find water near the heater or electrical, that’s the point to get a licensed plumber out to locate and assess it.
Before anyone does work, confirm they’re licensed. In California, plumbing contractors are licensed by the Contractors State License Board, and you can look up any license for free at cslb.ca.gov to check that it’s active and in good standing. It’s a two-minute step that protects you.
Catching a leak early is mostly about paying attention to the right number. Watch your usage, compare it to last year, and let the meter settle the question.