Find your shutoff before you need it
The first step in any leak is stopping the water, and most people learn where their main shutoff is while standing in an inch of it. Go and find yours this week, turn it to confirm it actually moves, and hang a tag on it.
| Valve | Where it usually is | Note |
|---|---|---|
| Main house shutoff | Basement or crawl space on the street-facing wall where the line enters. In slab-on-grade construction: the garage, a utility closet, or outside near the hose bib. | Gate valves that have not moved in twenty years often will not close fully or will not reopen. Test yours before you need it, and replace a seized one with a quarter-turn ball valve. |
| Curb stop | Under a small metal or plastic lid at the property line, near the meter | Needs a long curb key, and in many jurisdictions the utility asks that only they operate it |
| Fixture stops | Under each sink, behind each toilet | Handle every one occasionally so it does not seize. This is what lets you isolate one fixture instead of the house. |
| Water heater | Cold inlet at the top of the tank | Closing this stops a leaking tank while leaving the rest of the house on |
| Hose bibs | Often a separate shutoff inside the wall behind them | In freezing climates these get closed and the bib drained every fall |
Two situations override everything else on this page. Standing water anywhere near the electrical panel, or water running down inside a wall where circuits run: do not go in, do not stand in it to reach the breaker, call the power utility. A gas smell alongside water: leave the building and call the gas utility from outside without touching a switch. Neither is a DIY diagnosis.
Telling the four kinds apart
| Type | When it wets | How to confirm | What it usually needs |
|---|---|---|---|
| Supply line, pressurized | Constantly, whether or not anyone is using water. Gets worse, never better. | Meter test, below. A supply leak shows on the meter with every tap closed. | Plumber. Pressurized leaks do not wait. |
| Drain line | Only during and just after use of the fixture above | Run that one fixture hard for five minutes with someone watching below. Dry between uses is the signature. | Often a slip joint, a trap, or a shower pan. Cheaper than a supply leak. |
| Roof, flashing, or a window | During or shortly after rain, and worse in wind-driven rain | Correlate with the weather. Water travels along rafters, so the stain is often feet from the entry point. | Roofer. Check gutters first — overflowing gutters cause a surprising share of this. See gutter and downspout sizing. |
| Condensation | Humid weather, or cold weather on a cold surface. No connection to plumbing use or rain. | Look for a duct, an uninsulated cold-water pipe, or an exterior wall behind the wet spot. It is often a whole area of dampness, not a drip. | Insulation and humidity control, not plumbing. See insulation and condensation. |
The meter test
This is how you prove a leak exists before spending money on finding it, and it costs nothing.
Turn off every fixture and appliance that uses water — including the ice maker, the humidifier on the furnace, and any irrigation timer. Go to the meter. Most residential meters have a small triangular or star-shaped leak indicator that spins on any flow at all, however small. If it is moving with everything off, water is going somewhere. If there is no indicator, write down the reading, wait an hour without using water, and read it again.
To split the house from the yard: close the main house valve and repeat. If the meter still turns, the leak is between the meter and the house — a service line leak, which is expensive and, in most places, the homeowner's responsibility rather than the utility's. If it stops, the leak is inside.
Before assuming the worst, check toilets. A flapper that does not seat is the largest silent water waster in a typical house and can quietly add thousands of gallons to a bill. Put a few drops of food coloring in the tank, leave it 20 minutes without flushing, and look in the bowl. Color in the bowl means the flapper is leaking, and a flapper is a five-dollar part. If your bill jumped and you want to see what the volume actually costs, the water bill calculator converts it.
What it costs to find and fix
| Item | Typical range | What moves it |
|---|---|---|
| Plumber diagnostic visit | $100-$250 | Often credited against the repair. After-hours doubles it. |
| Leak detection — acoustic, thermal imaging, tracer gas | $150-$500 | Slab leaks and inaccessible walls cost more. Worth it: locating the leak within a foot rather than opening six feet of drywall pays for itself. |
| Accessible supply line repair | $200-$500 | Open basement or crawl space |
| In-wall or under-slab repair | $800-$4,000+ | Depends on whether the line is rerouted overhead or the slab is opened |
| Water heater replacement | $1,200-$2,500 installed | A tank leaking from the body is not repairable. See water heater running cost when comparing replacements. |
| Drywall, paint and flooring after | Often more than the plumbing | Budget for it separately. This is where the real number is. |
Do not open a wall to look before someone has located the leak. Detection exists precisely because guessing is more expensive than paying for the answer.
Who pays
| Situation | Usually |
|---|---|
| Owner-occupied house, leak inside | You. The repair is yours; the resulting damage may be a claim. |
| Service line between the meter and the house | Usually the homeowner, not the utility, in most service territories. Some utilities sell a service-line protection plan; check before you need it. |
| Renting | The landlord repairs the building. Report it in writing immediately, with photos, and keep the copy — a delayed report is the argument a landlord will make later. A renter's policy covers your belongings, not the structure. |
| Condo or HOA | The declaration decides it. Pipe inside your unit's walls is typically yours; a common stack or a main in a shared chase is typically the association's. Read the actual document rather than accepting a verbal answer. |
| Homeowner's insurance | Sudden and accidental discharge is generally covered, including damage to floors, walls and belongings. Gradual seepage over weeks or months is generally excluded, as is the failed part itself. Flood and groundwater need separate coverage. |
| High water bill from a leak | Many utilities have a one-time leak adjustment if you show a repair receipt. Call and ask — it is not usually advertised. |
The first hour
Close the nearest shutoff, then the main if you cannot isolate it. Kill power to the affected area at the breaker if it is safe to reach the panel dry. Photograph everything before you move it — wide shots and close shots, and get the date into the frame. Move belongings out and lift what you can off the wet floor. Then get air moving: fans and a dehumidifier running within the first day is the difference between drying a wall and replacing it, because mold gets going within about 24 to 48 hours on wet drywall. If it does take hold, mold removal covers what you can clean and what you cannot.
Go look at your main shutoff. Right now, before you close this page — that is the only item here you can do in advance, and it is the one that decides how bad the day is when a supply line finally lets go.
Questions people ask
How do I know if I have a hidden leak?
Run a meter test. Turn off every water-using fixture and appliance, including the ice maker and any irrigation timer, and watch the small leak indicator on the water meter — a triangle or star that spins on any flow at all. If it moves with everything off, water is going somewhere. If your meter has no indicator, note the reading, wait an hour without using water, and read it again. Before you panic, do a toilet dye test: a few drops of food coloring in the tank, 20 minutes, and any color in the bowl means a leaking flapper, which is a five-dollar fix and the most common cause of a mysteriously high bill.
Where is my main water shutoff?
In a house with a basement or crawl space, on the wall facing the street where the service line comes in, often near the meter. In slab-on-grade construction it is commonly in the garage, a utility closet, or outside close to a hose bib. There is also a curb stop under a small lid at the property line, which needs a long curb key and which many utilities prefer to operate themselves. Go find yours before you need it, and turn it to make sure it works — old gate valves seize, and discovering that mid-flood is a bad time. If it does not turn easily, have it replaced with a quarter-turn ball valve.
The ceiling has a stain but it is dry. Is it still leaking?
Maybe not, and that matters for the diagnosis. A dry stain that never grows is often an old event, but a stain that appears only after rain points at the roof or flashing, and one that appears only after someone showers upstairs points at the fixture, the drain or the shower pan. Circle the edge of the stain in pencil with the date and watch it. Water runs along framing before it drops, so the wet spot is frequently several feet from where the water actually enters, which is exactly why guessing and cutting is worse than paying for detection.
Will insurance cover the water damage?
The usual line in a homeowner policy is that sudden and accidental discharge is covered — a pipe bursting, a supply hose letting go, a water heater failing — including the damage to floors, walls and contents. What is generally excluded is gradual seepage over weeks or months, the failed component itself, and anything classed as flood or groundwater, which needs separate coverage. That distinction is why documenting the date matters: photograph everything before you clean up, keep receipts, and report promptly. If you rent, your policy covers your belongings; the structure is the landlord.
My water bill tripled and I cannot find a leak. What now?
Work through it in order. Toilet dye test on every toilet first, since a running flapper wastes more water than most people believe and makes no sound you would notice. Then the meter test with everything off. If the meter still turns after you close the main house valve, the leak is in the service line between the meter and the house — usually the homeowner responsibility, and a job for a leak detection service rather than a shovel. Also check irrigation, which fails silently underground. Once it is repaired, call the utility: many have a one-time leak adjustment against a repair receipt, and they generally do not offer it unless you ask.