The first call is the water utility, not a plumber
A high bill with no visible water is not yet a plumbing problem. It is a measurement problem, and the people who own the measurement are the utility.
Three things they do that no trade can:
They re-read the meter. A real share of shock bills are a misread, an estimated read from a month nobody visited, or a rate change nobody noticed. Free, one phone call, and it happens before you have spent a dollar.
They tell you which side of the meter the water is leaving. The meter is the usual dividing line between their pipe and yours. Loss on their side is their repair and their cost. Loss on your side is yours. Nobody else can settle that question, and a plumber who starts digging before it is settled may be digging in the utility’s easement.
Most run a leak adjustment policy. The names vary — leak adjustment, leak forgiveness, high bill credit — but the shape is consistent: an anomalous bill caused by a leak you have since fixed gets part of the excess credited back, usually once per property, usually only if you claim inside a window, and usually only against a repair invoice.
That last one is the most expensive thing people skip. They find the leaking toilet, fix it, pay the bill in full, and never learn the credit existed. Ask on the first call, before you spend anything: do you have a leak adjustment policy, and what do I need to document? The answer decides whether you keep the plumber’s invoice or throw it away.
The meter test, in fifteen minutes
Do this while you wait for the utility to call back. It costs nothing, and it is the one fact every trade you speak to afterward will ask you for.
- Turn everything off. Every faucet, the dishwasher, the washing machine, the ice maker, the irrigation timer, the humidifier, the pool auto-fill. Nobody flushes anything for the duration.
- Read the meter. Write down the full number. Most meters also carry a low-flow indicator — a small triangle, star, or dial that spins on almost no flow at all. If that indicator is turning with the house quiet, you have an active leak and you do not need to wait.
- Wait fifteen minutes, then re-read.
- Any movement is a leak. The number moved, or the triangle turned: water is going somewhere.
The EPA’s version of this test uses a two-hour window with no water use, which is the right call for a slow leak that fifteen minutes will not register. Run the short version first. If it comes back clean but the bill says otherwise, run it overnight.
Then isolate: inside the house, or under the yard
This second step separates a $200 problem from a $2,000 one, and it takes another fifteen minutes.
Find the main shutoff valve where water enters the house — usually the basement, crawlspace, garage, or a utility closet on the street-facing wall. Close it. Repeat the meter test.
- The meter stops → the leak is inside the house, past the valve. Fixtures, supply lines, toilets, or a slab leak.
- The meter keeps moving → the leak is between the meter and the house: the buried service line. On most properties that is your pipe, and it is the invisible kind that never surfaces in the yard because the water drains straight down. Water main repair runs $500–$2,000, national average around $1,000.
Tell whoever you call next exactly which of those two you got. It is the difference between a technician who knows where to start and one who bills you to find out.
The boring answer, more often than anything else: a toilet
A flapper that no longer seals lets tank water trickle continuously into the bowl and down the drain. No sound, no puddle, no symptom except the bill. Flappers are rubber — they harden and warp — and the EPA recommends checking them periodically and replacing them at least every five years.
The dye test settles it in ten minutes, per toilet:
- Take the tank lid off.
- Put a few drops of food coloring, or a dye tablet, into the tank water.
- Do not flush. Wait ten to fifteen minutes.
- Look in the bowl. Color in the bowl means tank water is escaping past the flapper.
Do every toilet, including the guest bathroom nobody uses — that is exactly where a leak runs a full billing cycle unnoticed.
The fix is cheap and often a homeowner part. A plumber’s flapper replacement runs $60–$120; a running toilet with more than the flapper worn runs $50–$400. Against a four-figure bill, that is usually the whole story.
For scale: the EPA puts the average family’s household leaks at 180 gallons a week — about 9,400 gallons a year — and finds nine percent of homes have leaks wasting 50 gallons or more per day. Thousands of gallons unaccounted for is not exotic. It is ordinary, and it is usually one small part.
The rest of the usual suspects
Work these roughly in this order — most likely and cheapest first.
Irrigation or sprinkler line. The biggest silent consumer on most properties. A cracked lateral or a valve that never fully closes runs underground, on a timer, at night, and the lawn above it looks fine or slightly greener. Shut the system off at the controller and re-run the meter test.
Outdoor spigots and hose bibs. Check every one, including the side of the house you never walk past. A hose left cracked open, or a frost-damaged bib leaking behind the siding, is common and entirely invisible.
Water softener stuck in regeneration. A softener that regenerates on a fault, or far more often than it should, sends water straight to the drain. If the unit is cycling with nobody using water, that is your leak.
Whole-house humidifier. The solenoid sticks open and water runs to the drain all season. Easy to miss on a furnace-mounted unit, because it sounds exactly like normal operation.
Pool auto-fill. An auto-fill will faithfully replace whatever a pool leak loses, converting a pool problem into a water bill problem with no visible symptom at all. Turn the auto-fill off for a day and mark the water line.
A slab leak — the expensive one. A supply line under the concrete foundation leaking into the ground beneath the house. The tells: a warm or hot spot on the floor (it is usually the hot line), the sound of running water with everything shut off, damp carpet or flooring with no source above it, and a foundation crack that appeared this year. Slab leak repair runs $1,000–$4,000, national average around $2,500, and rerouting the line instead of breaking the slab can reach five figures.
Who to call, and in what order
Utility → leak detection → plumber. Three parties, three different jobs.
Leak detection is its own trade. They arrive with acoustic listening equipment, thermal imaging, tracer gas, and pressure test gear, and the entire job is to mark an X on your floor or your yard. Many will not do the repair at all, which is precisely what makes them useful — no incentive to find an expensive problem. Detection runs $100–$400.
A plumber hunting blind costs more than detection does. Plumbers bill $75–$150 an hour, and the labor to find a leak inside a slab or under a yard is not plumbing labor, it is searching. Three hours of searching costs more than a specialist who arrives, listens, and marks the spot once. Worse, blind searching means opening drywall or concrete in the wrong place, and you pay to close that back up too.
Then the plumber repairs the located leak. With an X on the floor the job is bounded and quotable. An accessible leaking pipe repair runs $150–$350.
The one case where you skip detection: the meter test isolated the leak to inside the house, the dye test showed a toilet leaking, and there is nothing else to explain. Call the plumber, or change the flapper yourself.
If a quote makes you uneasy — especially a four-figure slab or service line number given before anyone located anything — check it against our quote sanity-check page first. Locating comes before quoting. A repair price for an unlocated leak is a guess with a decimal point on it.
If you rent
A huge bill with no visible leak is still the landlord’s repair. You may be responsible for the water you use, but you are not responsible for the plumbing that loses it, and a hidden leak is a maintenance failure rather than consumption.
Put it in writing the day you notice: the bill amount, the previous months for comparison, and your meter test result. Written notice is what starts the clock in most states and what protects you when the next bill arrives worse. If the answer is silence, the escalation ladder is on our landlord won’t fix it page — written notice, code enforcement, then the repair-and-deduct rules for your state.
Ask the landlord to file the leak adjustment too. It is normally the account holder who can claim it, and that may be them, not you.
Sequencing, so you don’t pay twice
- Call the utility. Re-read, which side of the meter, and the leak adjustment policy by name. Free.
- Meter test with everything off. Fifteen minutes. Free.
- Meter test again with the main valve closed. Inside the house, or the buried service line. Fifteen minutes. Free.
- Dye test every toilet. Ten minutes each. Free.
- Shut off irrigation, softener, humidifier, and pool fill, then repeat step 2. Free.
- Leak detection if it is still hiding — $100–$400 to find it.
- Plumber to repair what was found, invoice kept for the utility credit.
Steps 1 through 5 cost nothing and settle most of these. Only after them does anyone need to open a wall.
If the leak stops hiding and turns into water you can see, the clock changes and so does the page: a pipe letting go or water coming through the ceiling. And if a hidden leak ran long enough to wet the structure, the drying and rebuild work belongs to different companies than the plumber who fixes the pipe — who does what sorts out that lineup before anyone bills you twice for the same job.