If water is actively coming through a ceiling, running down a wall or pooling under the house, shut off the main water valve first. Our line is open 24/7, so call as soon as the water is stopped. Keep people away from wet ceilings that sag, and stay clear of outlets, switches and light fixtures near the water until the power to that area is off.
When a hidden leak is an urgent problem
Some leaks can wait for a daytime appointment, and some cannot. Water that is still flowing, a ceiling that is bulging, or a meter that spins with every fixture closed all count as urgent, because the damage grows by the hour. We take those calls overnight and on weekends, and we aim to get a technician out the same day when schedules allow.
Slow leaks matter too, even if they are not an emergency right now. A faint damp smell, a patch of paint that keeps peeling, or a floor that feels warm in one spot can mean a line has been weeping for months. Finding it early is cheaper than repairing the framing, flooring and mold that follow.
A stain that grows after rain is not always the roof
A ceiling stain can come from the roof, an upstairs bath or a supply line. We check whether the stain changes when fixtures run, which separates a plumbing source from weather.
Sound of water with everything off
A hiss or trickle in a wall or under a floor usually means a pressurized supply line. Turn on nothing, listen at the stain, and tell us where you hear it loudest.
Warm spots on a floor
A warm patch can point to a hot water line leaking beneath a slab or subfloor. It is a clue worth reporting even if the floor feels dry.
Meter movement with everything closed
If the meter dial or low-flow indicator moves when no fixture is running, water is escaping somewhere. We then work out whether it is inside the house, in the yard or under the driveway.
Crawlspace dampness
Soft soil, a musty smell or condensation under the house can come from a drain or supply leak. The crawlspace often shows the problem before the rooms above do.
How we trace a leak without tearing things open
The point of detection is to cut as little as possible. We start with questions and simple checks, then use equipment only where it is needed.
Confirm it is a plumbing leak
We ask where and when you notice it and look at the stain, the nearest fixtures and the meter. This rules out roof, condensation and appliance causes before any equipment comes out.
Isolate the line
By closing valves and watching the meter or pressure, we narrow down whether the leak is on a supply line, a drain or the section between the street and the house.
Pinpoint with equipment
Acoustic listening, thermal imaging and pressure testing show where the water is escaping. We mark the spot so any opening is small and in the right place.
Open only where needed
If a repair is needed, we cut the smallest practical access and explain what the opening will look like afterward. Anything that needs patching, painting or flooring work is for a separate trade.
Repair or recommend
Where the fix is simple we can repair the line. If the leak is under a slab or points to failing pipe, we explain options such as slab leak repair or replacement so you can decide.
How Millbrae water service shapes a leak search
Millbrae runs its own water utility, buying all of its supply from the San Francisco regional system. The city's water system reports 11 pressure zones and about 69.7 miles of mains. Static pressure can therefore differ from one street to the next, and a house with higher pressure puts more stress on old joints and pushes more water through a small leak.
Water and sewer service in Millbrae is run by the city's Public Works Department. If the meter keeps moving with every fixture closed, we trace whether the loss is inside the house or in the buried line leading to it, and we tell you which agency or trade to involve next.
Millbrae specifics worth knowing
About two-thirds of the city's housing is single-family detached, and a large part of the stock dates from the 1950s building boom, when dwelling units rose from 2,783 to 4,803 in ten years. Homes from that era may still have original galvanized steel or early copper lines. Those pipes tend to fail at fittings and low points, and they sometimes leak where you cannot see.
Millbrae water arrives treated with chloramine and averages about 62 ppm hardness in the city's latest water quality report. That is on the soft side, so mineral scale is less likely to be what clogs or seals a pinhole. Leaks here are more often a matter of pipe age, soil movement and pressure than of heavy scale.
If a leak means cutting into walls or floors, permits may apply, and the Millbrae Building Division handles plumbing permits. We will tell you before we start whether the repair is likely to need one.
Detection compared with guessing
| Approach | What you get | Risk |
|---|---|---|
| Opening the wall where the stain is | A hole in the drywall | The leak is often not directly behind the stain |
| Waiting to see if it dries | Time | Mold, rot and a growing repair |
| Dye or food coloring tests | Some answers on toilets | Does not help with pipes in walls or slabs |
| Leak detection with a plumber | A marked spot and a plan | Costs a visit, saves cutting in the wrong place |
What affects the cost of leak detection
What changes the price of leak detection
Detection is priced by the work needed to find the source, not by how bad the stain looks.
Where the leak could be
A single bathroom wall is quicker than an entire house or yard.
Access to pipes
Crawlspaces and attics are easier than finished slabs.
Equipment used
Listening, thermal and pressure testing add time to the visit.
Repair after detection
Finding the leak and fixing it are separate tasks with separate costs.
Time of day
Overnight and weekend visits are priced differently from scheduled ones.
Call the 24/7 line for a clear price before work starts. Homeowner insurance may cover resulting water damage in some cases, so ask your insurer early.
Seeing a stain and not sure where it starts?
Tell us where the damp or sound is and whether the meter is moving. We will say what to shut off and when we can come.
Where leak detection leads next
A running meter and a surprising bill often go together, and our guide to high water bills and meter leaks explains how we separate a leak from heavy use. If a line has burst or is spraying, go straight to burst pipe repair.
We also serve Burlingame and the other places on our service area page. A call from the Millbrae Station area, Green Hills or downtown El Camino Real gets the same 24/7 dispatch.
Leak detection questions
Yes. The line is staffed 24/7, and an active leak at night is treated as urgent. We will tell you which valve to close while you wait and what we can arrange for your address.
We combine questions, meter and pressure checks, acoustic listening and thermal imaging. That usually narrows the source to a small area, so any opening in the wall is small and placed where the pipe actually is.
Not always. Water travels along framing, so the visible stain may be some distance from the source. We locate the leak first and only recommend opening if a repair needs access.
Close the main valve at the house and watch the meter. If it stops, the leak is inside the house. If it keeps moving, the loss is somewhere in the buried line. We can confirm which, and explain what comes next.
Usually yes. Listening equipment and thermal imaging can trace a line under a slab to a small area. Opening the slab only happens when you choose a repair, and we explain the alternatives first.
Not usually from one leak. Repeated leaks along the same older line, however, suggest the pipe is failing. We tell you plainly where the pipe stands and let you weigh repair against replacement.
It can. If the meter moves with everything off, finding the leak is the next step. If it does not, the bill may come from usage, and we say so.
Simple repairs often are not, but permits may apply for larger work, and the Millbrae Building Division handles plumbing permits. We will tell you what applies before work starts.
Sources and standards: The City of Millbrae 2025 Water Quality Report. The City of Millbrae Public Works water pages. The California Plumbing Code (based on the Uniform Plumbing Code).