The short answer
A sudden jump in your water bill almost always means a hidden leak — most often a running toilet, but sometimes an irrigation leak, a slab leak, or a failing water service line. You can narrow it down quickly with your meter, and a leak-detection visit pinpoints the rest before the waste adds up.
Why does a bill spike usually mean a leak?
Water is metered, so if your usage hasn't changed but the bill has, water is going somewhere you're not seeing. A surprising amount can escape silently: a single running toilet can waste thousands of gallons a month, and an underground service-line leak can run nonstop without ever showing inside the house.
The usual suspects, most to least common
Where the water is usually going:
- A running or 'phantom-flushing' toilet — the #1 hidden waster, often silent
- Dripping fixtures and worn faucet cartridges — small but constant
- Irrigation leaks or a stuck valve — easy to miss since it's outdoors
- A slab leak — a supply line leaking under the foundation (warm floor spot, running-water sound)
- A failing water service line — soggy spots in the yard, dropping pressure
How to check it yourself in 20 minutes
A quick DIY meter test:
- 1Turn off every water fixture and appliance in and around the home
- 2Find your water meter and note the reading (or watch the leak-indicator dial)
- 3Wait 20-30 minutes without using any water
- 4Check the meter again — if it moved, you have a leak somewhere on your side
- 5Drop a few drops of food coloring in each toilet tank; if color appears in the bowl without flushing, that toilet is leaking
Start with the toilets
Because toilets are the most common culprit and easiest to test, check them first with the dye test before assuming the worst.
When to call a plumber
If the meter keeps moving with everything off and the toilets test clean, the leak is likely hidden — in a wall, under the slab, or in the service line. That's when professional leak detection pays for itself: we locate the leak precisely so the repair is targeted, not exploratory.
What's the next step?
If you've confirmed a leak you can't find, book leak detection. We'll pinpoint the source — fixture, slab, or service line — give you a flat-rate repair price, and stop the waste before another bill arrives.
Yes. A continuously running or silently leaking toilet can waste thousands of gallons a month, which shows up clearly on a bill. It's the most common cause of a sudden spike and the easiest to test with a dye test.
Signs include a warm spot on the floor, the sound of running water with everything off, an unexplained bill spike, or cracks in the slab. Professional leak detection confirms it without tearing up the floor to look.
Terms in this guide
- Slab leak
- A water-line leak in or beneath the concrete foundation slab of a home. Common signs include a warm spot on the floor, the sound of running water with everything off, an unexplained spike in your water bill, or cracking in the slab.
- Water service line
- The pipe that carries clean water from the city main (or your well) to your home. When it leaks or fails, it can cause low pressure, soggy spots in the yard, or a high water bill.
- Pressure-reducing valve (PRV)
- A valve that lowers and stabilizes incoming municipal water pressure to a safe level (typically 50–75 PSI). Too-high pressure stresses fixtures, water heaters, and joints, and can void appliance warranties.