Quick answer: To find a hidden leak: check your water meter with everything off — if it still moves, you have a leak. Then look for warm/wet spots on floors, stains on ceilings/walls, a spike in your water bill, the sound of running water, or mold smell. A cheap water leak detector near at-risk spots catches leaks early.
A licensed plumber’s method for finding leaks fast.
Step 1: The Meter Test
Turn off every water fixture and appliance. Check your water meter, wait 1–2 hours with no usage, and check again. If it moved, water is escaping somewhere.
Step 2: Hunt for Signs
- Stains or sagging on ceilings and walls
- Warm spots on the floor (hot-water line leak)
- Musty smell or mold
- Unexplained jump in the water bill
- Sound of trickling water with everything off
Step 3: Check the Usual Suspects
Toilets are the #1 silent leaker — add food coloring to the tank; if it shows in the bowl without flushing, the flapper is leaking (see our running toilet guide). Then check under sinks, the water heater, and supply lines.
Step 4: Prevent the Next One
Put water leak detectors near the water heater, washing machine, and under sinks. They alarm the moment water appears — cheap insurance against a flooded home.
When to Call a Plumber
If the meter confirms a leak but you can’t find it, it may be inside a wall or under the slab — call a pro with leak-detection equipment. For a burst you can see, our emergency pipe guide shows how to stop it.
FAQ
How do I find a water leak I can’t see?
Do the meter test: shut off all water, note the meter, wait 1–2 hours, and check again. Movement means a hidden leak. Then look for stains, warm spots, and mold smell.
How do I know if my toilet is leaking?
Add a few drops of food coloring to the tank. If color appears in the bowl without flushing, the flapper is leaking.
Can a hidden leak raise my water bill?
Yes — significantly. A sudden, unexplained bill increase is one of the most common signs of a hidden leak.
Related: Why is my water bill so high?
To stop the next leak automatically, a smart shutoff valve closes your main when it detects a problem.
For a leak specifically under the kitchen sink, our kitchen sink leaking underneath guide narrows it down by drain side vs. supply side.
Found the leak but not sure what the repair runs? Our 2026 Plumbing Repair Cost Index lists pipe-leak repair prices, low to high.
To see exactly what’s wrong inside the line, see our best sewer inspection camera guide.
Fix the 12 Most Common Plumbing Problems Yourself — Free Plumber’s Handbook — including how to tell if your water heater is about to fail
Step-by-step fixes for the 12 most common problems — and exactly when to call a pro. Free and instant, from a licensed plumber. Save hundreds on calls you didn’t need.