Your Water Bill Doubled: How to Find a Hidden Leak

Your usage hasn’t changed, nobody’s filled a pool, and the bill has doubled. That water is going somewhere. Here’s how to narrow down where before you call anyone.

Step 1: The meter test

This settles whether you have a leak at all, in about fifteen minutes.

1. Turn off every tap, appliance, ice maker and irrigation controller in and around the house.
2. Find your water meter, usually in a box near the street.
3. Look for the low-flow indicator — a small triangle, star or dial that spins on tiny amounts of flow.
4. If it’s moving with everything off, water is escaping somewhere.
5. Note the exact reading, wait two hours with no water used, and read it again. Any change confirms it.

Step 2: Inside or outside?

Find your main shutoff valve where the supply enters the house and close it. Then check the meter again.

Still moving? The leak is between the meter and the house — an underground service line or irrigation. Stopped? It’s inside.

Step 3: Rule out the toilet

Toilets are the single most common cause of a mystifying bill, and a leaking flapper is silent. Put a few drops of food colouring in the tank, wait thirty minutes without flushing, and check the bowl. Colour in the bowl means the flapper is passing water continuously. That one fault can waste hundreds of gallons a day, and the part costs a few dollars.

Step 4: Irrigation

A cracked lateral or a stuck valve runs entirely underground and shows up only on the bill. Look for one zone that’s greener than the rest, a permanently soggy patch, or heads that weep between cycles.

Step 5: The hidden ones

If the meter says inside, the toilets are clean and irrigation checks out, you’re looking at supply pipework in a wall, ceiling or slab. Signs to look for:

• A warm spot on the floor — that’s a hot water line under the slab.
• Running water audible with everything off.
• Bubbling paint, stained drywall, or a musty smell in one room.
• Pressure that’s dropped across the whole house.

Slab leaks are common in Southern California because so much supply pipework runs in concrete. Our guide to slab leaks covers causes and repair options.

When to stop and call

Once you’ve confirmed a leak and ruled out toilets and irrigation, DIY has done what it can. Locating a pressurised leak inside a wall or under a slab needs acoustic equipment and thermal imaging — otherwise you’re opening walls on a hunch.

Also worth knowing: many water utilities will adjust a bill inflated by a documented leak, but usually only once and usually with a plumber’s report. Fix it, get it in writing, and ask.

Get it located

Leak detection across San Dimas, La Verne, Pomona and Claremont. Call (949) 355-5640.