If your water bill spiked, you heard water running with everything off, or you found a damp spot you can’t explain, you probably have a leak somewhere. Here’s how to track it down systematically so you can give a plumber useful information when you call.
Start at the Meter
This is the fastest way to confirm a leak exists and get a rough sense of its size.
Find your water meter, usually near the street or sidewalk in a small covered box. Turn off every fixture in the house, including the icemaker and any irrigation. Don’t flush, don’t run a tap, don’t start the dishwasher.
Now look at the meter. Most residential meters have a small triangle or dial, sometimes called a leak indicator, that spins when water is moving. If it’s moving with everything off, water is flowing somewhere it shouldn’t.
For a more definitive test: write down the meter reading, leave the house for 30 minutes without using any water, come back and check again. If the number changed, you have a confirmed leak. The amount it changed tells you roughly how fast it’s losing water.
One thing to note: if you have an irrigation system or a secondary meter for outdoor use, make sure those valves are off too.
Check the Toilets First
Toilets account for a surprisingly large share of household water waste. A running toilet can lose anywhere from a few gallons to hundreds of gallons per day depending on what’s failing, and you won’t always hear it.
The dye test is simple. Drop a few food-coloring drops (or a dye tablet, sold at hardware stores) into the tank, not the bowl. Wait 10 minutes without flushing. If color shows up in the bowl, the flapper isn’t sealing and water is bleeding through constantly.
Check the float, the fill valve, and the overflow tube while you’re at it. If the water level is sitting at or above the overflow tube, it’s running directly into the bowl. You’ll sometimes hear a faint hiss.
Do this for every toilet in the house.
Look at the Obvious Spots Under Sinks
Pull open every cabinet under every sink. Look at the supply lines (the braided hoses connecting the shutoff valves to the faucet), the drain connections, and the P-trap. You’re looking for moisture, mineral deposits (white or greenish crust), or standing water.
Run the sink and watch the drain connections while water is flowing. Slow drips under load are easy to miss when everything is dry.
Do the same for the dishwasher. Pull it forward slightly if you can, or check the cabinet floor next to it.
Hot Water Heater
Go look at the base of your water heater. A small puddle or rust staining at the bottom usually means the tank is corroding from inside. Check the pressure relief valve too, which is a valve with a small lever on the side, usually draining to a pipe near the floor. If it’s dripping, that’s worth attention.
Also check the supply connections at the top of the unit.
Behind Walls and Under Floors
This is where leaks get harder. Signs that water is hiding somewhere you can’t see:
- A wall that feels soft or has bubbled paint
- Flooring that’s buckled, soft, or stained
- A musty smell in a specific spot that doesn’t go away
- Discoloration on a ceiling (usually from an upstairs bathroom)
- A warm or cold spot on a concrete slab floor (can indicate a slab leak from a hot or cold water line)
Press on drywall in bathrooms around the tub and shower surround. Soft spots mean moisture has been there for a while.
If you can access the crawl space, go look. Wet soil, standing water, or mineral deposits on pipes are all worth noting.
Irrigation and Outdoor Spigots
Check each hose bib (outdoor faucet) for drips. A slow drip at the handle usually means the packing nut is loose or the seat washer is worn.
For irrigation systems, run each zone manually and walk the lines. Look for sections that stay wet after a cycle ends, heads that don’t retract, or a zone that seems to use more water than the others.
When to Call a Licensed Plumber
The checks above help you pin down where the problem is. At that point, the next step is a licensed plumber, not a repair attempt.
If your meter is still moving and you couldn’t find the source at any visible fixture, the leak is hidden. That means a supply line inside a wall, a slab leak, or something on the main. These require pressure testing, acoustic listening equipment, or thermal imaging to locate accurately. Guessing and opening walls without that data usually makes things worse and costs more.
Leaks you can see, like a dripping pressure relief valve, a cracked drain fitting, or a corroded water heater, may also involve permits depending on scope. In California, plumbing work beyond basic owner-maintenance requires a licensed C-36 contractor.
Before anyone starts work, verify their license at cslb.ca.gov. Enter the contractor’s name or license number, confirm it’s active, and confirm the C-36 classification. That takes two minutes and protects you if something goes wrong.