Is the water coming from under the slab?

Almost every house in Orange County sits on a concrete slab, and the plumbing runs through it. That makes one question harder here than almost anywhere else: is the water arriving from under the floor, or from something above it? These five questions sort the evidence.

This is about plumbing and concrete, and nothing else. It reads what you tell it about water, floors and pipes. It is not a leak detection service: it cannot listen to your slab, and a line under concrete is located with equipment, not with a questionnaire.

Nothing is sent anywhere. This runs entirely in your browser, there is no form, and nothing you choose leaves this page.

Slab leak check

What made you suspect something? With every tap and appliance off, did the water meter move? When do you notice it? Where in the house is the sign? How old is the plumbing?

Water almost never surfaces where it started. It travels first, and shows itself late. The supply lines run inside or beneath the concrete, which is why a leak down there reaches the floor covering long before anybody sees water.

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1 AC condensate. The pan overflows up in the attic and finds the ceiling below it.
2 The ceiling stain. It marks where the water arrived, not where it started out.
3 A burst supply line. Pressurized pipe inside a wall, running until the main is shut.
4 The water heater. Often in the garage, and its failure runs toward the house, not away from it.
5 A slab leak. It travels sideways under the concrete and surfaces long after it began.

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Describe what you are seeing and you will be connected with an independent provider covering your area.

The meter test, which costs nothing

Turn off every tap, the ice maker, the irrigation and anything else that draws water, then find the meter at the street and note where the small dial or triangle sits. Leave it two hours and look again. If it has moved and nothing was used, water is leaving the system somewhere between the meter and the house.

That does not yet prove the leak is under the slab. It proves there is a leak, and that is the finding that turns a vague worry into something a plumber can act on. Locating it under concrete is done with acoustic and pressure equipment, which is the part worth paying for.

Why the hot side fails first

Most slab leaks in houses of this era are on the hot water line. Hot water moves faster through a smaller line, the pipe expands and contracts every time it is used, and it spends its life rubbing against the concrete it passes through. That combination wears a copper line from the inside and the outside at once.

It is also why the warm patch on the floor is such a useful sign. Cold water escaping under a slab does not announce itself; hot water heats the concrete above it, and the floor tells you.

Use this page

This tool may be reproduced or linked to freely, with attribution to ocwaterandmold.com. If it is useful to a homeowners association, a property manager, a real estate office or anyone putting together information for owners of slab-built houses, it is meant to be shared.

If the water has already reached flooring or drywall, the question changes from finding it to drying it. The water damage side covers extraction and drying, and the inspection side covers what a long, slow leak leaves behind.