Saving waterGuide
How to find a water leak in your house: five places to check first
Start with the toilets: add a few drops of food coloring to each tank, wait 15 minutes, and if color reaches the bowl, it leaks. Then check faucets and showerheads, under the sinks, and under the water heater and appliances. If you find nothing but your water meter still moves with everything off, call a plumber.
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You know the sound. The toilet down the hall hisses and refills at 2 a.m., and nobody flushed it.
That's a leak, and it's the most common kind inside a home.[1] Many common leaks are quick to find and easy to fix.[2] Below are five places to check, starting with the most common, and what to do when you find one. Water pooling or spraying? Close your main shut-off valve, usually on the pipe outside the front or side of the house, below an outdoor faucet. Turn it by hand, then call a plumber.[3]
Why toilets first? One running toilet can waste about eight times as much water in a year as all the leaks in an average home put together.
1. The toilets
Toilet leaks are often silent, so they go unnoticed.[1][4] A running toilet can waste 200 gallons a day or more,[5] as much water as 15 showers a day.[6]
- Do the dye test. Lift the tank lid and add a few drops of food coloring to the water in the tank. Don't flush. Wait 15 minutes. If color shows up in the bowl, the toilet leaks.[1] Flush afterward so the color doesn't stain.[7]
- If it leaks, look at the flapper first. It's the rubber seal at the bottom of the tank, and a worn one is by far the most common cause.[4] Check that the chain that lifts it isn't catching on anything.[1] If the flapper is worn, a new one is a quick, inexpensive fix.[5] Turn off the water first at the supply valve, the small knob on the pipe behind the toilet, and take the old flapper to the hardware store so you get one that fits.[1][7]
- Still running? Look at the water level. The overflow tube is the open pipe standing up in the tank. If the water reaches its top, it's spilling down the tube, and the fill valve, the part that refills the tank, may need adjusting or replacing.[4]
Our take: wait the full 15 minutes. Some guides say 10, but a slow leak can take longer to show.[7][1]
2. Faucets and showerheads
A drip is easy to tune out, but it adds up: one drip a second is more than 3,000 gallons a year, enough for 180 showers.[7]
- Faucets: a common cause is a worn washer or gasket, a rubber seal inside the faucet.[7][1] If you're handy, it's often a simple repair; if not, call a plumber.[4]
- Showerheads: tighten the connection to the pipe and wrap the threads with pipe tape, a thin tape sold at most hardware stores.[7]
3. Under the sinks
Open each cabinet with a flashlight. Look for standing water, rust around pipe joints or a bowed cabinet floor.[2][1]
Notice which pipe is wet. A leak where the sink connects to its drain, the wide pipe that carries water away, doesn't waste water or raise your bill.[6] It can still damage the cabinet and floor, so fix it soon.
4. The water heater and the appliances
- The water heater: look under the tank for a puddle or rust.[2][1] If you see either, call a licensed plumber.[2]
- The washer, dishwasher and a fridge with an ice maker: check for water underneath. It can mean the supply line, the hose that brings water in, is leaking.[2] Call a plumber for that too.[2]
- Run them and watch. Some appliance leaks only show while the machine is running.[1]
5. Still nothing? Use your water meter
If the first four checks come up dry, your water meter can tell you whether something is still leaking. It's usually in a box near the curb, under a lid that may say "water".[8]
- Turn off every tap and every appliance that uses water, then watch the meter's small star, triangle or gear. If it turns, water is going somewhere.[8] If it holds still, write down the numbers on the meter, use no water for two hours, and read it again. Any change probably means a leak.[2] Our take: use the two-hour wait. A short check can miss a small leak.[4] Our guide to finding a water leak underground shows how to tell a leak in the house from one in the yard.
- If the leak is in the house, look for damp spots and water stains on ceilings and walls.[3]
- Feel the floor for warm spots after running hot water nearby. In a house built on a concrete slab, with no basement or crawl space, that can mean a hot water pipe leaking under the floor. Most leaks in pipes inside a house are on hot water lines, so check near those first.[3]
- Follow your nose. A musty smell with no source you can see can mean hidden mold, for example inside a wall around a leaking pipe.[9]
- Then call a plumber, ideally one who does leak detection.[3] Moisture or mold on walls, ceilings or floors calls for a professional.[2]
If anything got wet, dry it within 24 to 48 hours. In most cases, mold won't grow then.[9] For a big soak, a water damage specialist can help.[9]
Cold nights ahead? See how to winterize outdoor faucets so one doesn't crack.
In Sonoma County
- Free dye tablets: small tablets that color the tank water, free at Healdsburg City Hall.[10] Healdsburg and Sonoma both call toilet leaks the number one cause of high water bills.[10][11]
- A free check at home: Cotati's free water use survey includes a search for hidden leaks; call the Sonoma-Marin Saving Water Partnership, (707) 547-1909.[12] Elsewhere, ask your water utility.
- A bill credit: some cities here take part of the bill off once a leak is fixed, Healdsburg among them.[10] Our underground leak guide lists them.
What it means for you
- Tonight, dye-test every toilet. It costs a few drops of food coloring.
- This weekend, take a flashlight under each sink, the water heater and the washer.
- If the bill is what sent you here, our guide to high water bills shows what else can push it up.
Then listen at 2 a.m. A quiet toilet is a good sign.
Sources
- 1. Arizona Municipal Water Users Association, Smart Home Water Guide: Indoor Visual Leak Inspection
- 2. US EPA WaterSense, Detect and Chase Down Leaks Checklist
- 3. Arizona Municipal Water Users Association, Smart Home Water Guide: Isolation Method for Continuous Leaks
- 4. Alliance for Water Efficiency, Home Water Works: Leaks
- 5. US EPA WaterSense, Fix a Leak Week Family Fact Sheet
- 6. Saving Water Partnership (Seattle area), Leaks
- 7. US EPA WaterSense, Fix a Leak Week (updated March 13, 2026)
- 8. Arizona Municipal Water Users Association, Smart Home Water Guide: How to Read Your Water Meter
- 9. US EPA, A Brief Guide to Mold, Moisture and Your Home
- 10. City of Healdsburg, Read Your Water Meter and Identify Leaks
- 11. City of Sonoma, Take the Dye Tab Challenge: Find and Fix Hidden Toilet Leaks
- 12. City of Cotati, Free Water Use Surveys
Checked 2026-11-07. Rules and programs change. If something here is out of date, the source above wins. Spot an error? See our corrections policy.
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