Slab Leak Warning Signs

By the Westminster Emergency Plumber team · Updated September 2026

Which Homes Have Lines Under Concrete

People assume this is not a problem in a part of the country where nearly every house has a basement. Plenty of properties here do have water lines running under or through concrete: slab-on-grade patio homes and townhomes, garden-level and walkout builds where part of the footprint sits on a slab, additions poured over an existing run, and the garage or utility slab carrying a line out to a hose bib or a laundry sink. Any of those can develop the same kind of hidden leak.

The soils here add to it. The expansive clay along the Front Range swells when it is wet and shrinks when it dries, and concrete sitting on it moves with the seasons. Pipe cast into or buried under that concrete takes the strain.

A Warm Patch on the Floor

This is the classic sign and the easiest one to notice. If a hot water line under a slab is leaking, the concrete above it warms up, and you feel it walking barefoot or you notice a pet choosing to lie in the same spot. A cold line leaking produces no such clue, which is part of why cold-side leaks run longer before anyone catches them.

Not every warm floor is a leak. Radiant heating, a sunny window and a nearby duct all do it too. Treat it as one sign among several rather than proof on its own.

The Sound of Water With Nothing Running

Late at night, with the house quiet and everything off, stand still and listen near the floor. A faint hiss or a sound of running water where there should be none is a genuine indicator. It is also one of the few signs that appears early, before the water bill has had time to say anything.

Run the Meter Test

This is the most useful thing a homeowner can do, and it takes ten minutes. Turn off every faucet, appliance and ice maker, and make sure nobody flushes anything. Go to the water meter and note the reading, including the small sweep hand or the leak indicator if it has one. Wait half an hour without using any water, then read it again.

If the reading has moved, water is escaping somewhere in the system. That does not tell you it is under concrete, but it does tell you it is a plumbing leak and not groundwater. It is the single piece of evidence a plumber most wants to hear about when you call.

The Bill and the Flooring

A bill that climbs month after month with no change in how the house is used is worth taking seriously, especially in winter when there is no irrigation to blame it on. Look at the pattern rather than one high month.

Flooring gives its own warning. Laminate that has started to cup, tile grout that keeps discoloring in one area, or carpet that smells musty in a corner over concrete all point at moisture underneath. Hot water pressure dropping while the cold stays normal is another quiet clue, because it suggests the loss is on the hot side.

What Not to Do While You Wait

Do not break up concrete to look. Locating a leak accurately is a technical job with pressure isolation, listening equipment and thermal checks, and opening the floor in the wrong place is expensive in a way that cannot be undone. Do not ignore it either, because water running under a slab keeps soaking the soil beneath it, and saturated expansive clay is the last thing you want under a floor.

If the leak is confirmed and you cannot get a visit for a day or two, ask about isolating the affected line rather than shutting off the whole house, so you still have water in the meantime.

How the Repair Decision Goes

Once the leak is located there are usually two routes. A single break in a reachable spot can often be repaired in place by opening a small section of floor. A line that has failed before, or that sits somewhere awkward, is frequently better abandoned and rerouted overhead. The reroute costs more on the day and can be cheaper over several years, and an honest quote sets both out rather than assuming for you. Our slab leak repair page explains what the work covers.

Leaks Under Concrete Around Westminster

Across Westminster and the north metro towns, the properties that raise this most often are townhomes and patio homes, garden-level units, and garage or addition slabs in otherwise ordinary basement houses. Manufactured homes have their own version of the problem, with supply lines running under the floor rather than under concrete, which is a common call in Federal Heights. In every case the answer starts the same way: confirm that water is escaping, then find out where.

Arrange an Inspection

If the meter is moving with everything off, call. Westminster Emergency Plumber confirms the loss, narrows it down and prices the locating work and the repair separately, so you are not approving a repair before anyone knows where the leak is. Read more about leak detection, see how a service call works, or check where we work.