Most plumbing failures are loud. A burst hose, a dripping ceiling, a puddle under the sink. The leak that runs inside or beneath a concrete slab is different. It may produce no sound, no stain and no puddle for months. The first sign is often a water bill that seems wrong, a warm patch of floor, or a crack that wasn’t there last season.
In Del Mar, where many homes are second residences or seasonal rentals, that quiet can stretch further. Nobody is home to notice the floor feels warm or that the water heater runs more often. This entry is about closing that gap.
A pipe you will never see
Many slab-on-grade homes, including a good share of the post-war and later houses in the Del Mar Heights area, have water supply lines that run beneath or within the slab. Copper was common for decades. Where those lines pass through concrete, rub against aggregate or sit in damp soil, they can wear over time. Pinhole leaks are the familiar result.
Not every leak beneath a slab is the supply line. Drain lines can crack or separate at joints, and they leak only when water is running, which makes them harder to catch. Both types send water into the soil under the floor.
The meter and the line to the house
The City of Del Mar’s water FAQ explains that the meter sits on the private line connection, usually between the home and the street. The City encourages owners to install a separate shutoff valve on their side of the meter, and it asks owners not to shut off the City’s meter themselves.
That owner-side valve matters more than it seems. When a leak is suspected, being able to turn off water to the house without touching the City’s equipment is the first practical step. If a home doesn’t have one, adding it is a sensible, modest project. Owners in Carmel Valley or other areas served by a different provider should follow that provider’s guidance; the principle is the same.
Reading the meter at rest
The City’s guide to reading a residential meter describes a simple test. Turn off all water inside and outside the house. Look at the meter’s low-flow indicator, the small white triangle. If it spins, water is moving through the meter. Note the reading, wait fifteen minutes without using water, and read it again. A change means water is flowing somewhere.
EPA’s WaterSense program suggests a longer version: read the meter before and after a two-hour period when no water is used. If the reading changes at all, there is probably a leak.
For a second home, the longer test fits naturally into arrival or departure. Read the meter as you leave, note the number, and read it again on return, provided irrigation and automatic fill valves were off. A caretaker can do the same.
Making sense of the reading
Del Mar’s guide notes that residential meters read in cubic feet, and one cubic foot is about 7.48 gallons. A small movement over fifteen minutes can add up to a meaningful amount over a month.
EPA puts the scale in context: the average household’s leaks can waste more than 9,300 gallons a year, and nine percent of homes have leaks that waste 50 gallons or more a day. Most of those are toilets, faucets and valves. Before assuming the worst, rule those out. A toilet flapper is far more likely than a slab leak. If the meter still moves with every fixture checked and irrigation off, the search narrows.
Signs inside the house
Beyond the meter, the quieter signals tend to be these:
- a section of floor that feels warm underfoot, which points toward a hot water line,
- the sound of running water when nothing is on,
- a water heater that cycles more than usual,
- flooring that lifts, cups or loosens in one area, or a musty smell from baseboards,
- damp carpet or tack strip with no obvious source,
- new cracks in the slab or in tile set on it.
None of these is conclusive on its own. Together with a moving meter, they justify calling a leak-detection plumber.
What water does to the ground beneath
This is where a plumbing problem can become a structural one. A slab rests on soil, and the residential code assumes that soil behaves in a predictable way. Code also addresses expansive soils specifically, because clay that gains moisture swells and clay that loses it shrinks. A steady leak adds water where none was expected.
Depending on the soil, the result can go in either direction. Clay soils may swell and lift part of the slab. Sandy or poorly compacted fill may wash or soften and let part of it settle. Either can show up as cracks, uneven floors or doors that begin to bind. Our slab foundation repair page describes how those patterns are read, and our settlement repair page covers the dropping side.
Sequencing the specialists
When a slab leak is suspected, the plumbing comes first. A plumber locates and repairs the leak, by rerouting the line through walls or ceilings, or by opening the floor at the leak. Only after the water has stopped does it make sense to judge the structure, because a slab sitting on wet soil may still be changing.
After the repair, give the ground time to settle into a new normal, then look again. If cracks are widening, floors have moved out of level, or doors have changed behavior, a structural evaluation helps determine whether the slab needs anything beyond cosmetic repair. When structural questions arise, we coordinate with licensed engineers as needed.
Rerouting versus opening the floor
The plumbing decision has a structural consequence that owners often overlook. Rerouting leaves the slab untouched but abandons the old line in place. Opening the floor gives direct access but cuts the concrete, which then must be patched. If the floor is post-tensioned, cutting it requires special care, because the tendons inside carry tension. Ask the plumber whether the slab is post-tensioned before any saw touches it.
The absentee owner’s version
For homes that sit empty, a few habits help:
- Shut the water off at the owner-side valve when leaving for extended periods, where the household setup permits it.
- Record the meter reading on departure and arrival.
- Ask a caretaker or property manager to check the meter during long absences.
- Keep a short log of floor cracks and door behavior, with dated photos, so changes are visible later.
Our second-home monitoring page describes how we support owners who are often away.
Factors in a slab-leak follow-up
How long the leak ran, the soil type beneath the home, whether the slab is conventional or post-tensioned, the extent of floor movement, and access through finished interiors all influence the scope of any structural follow-up. Flooring removal and restoration are separate considerations.
We serve all of Del Mar, including the beach neighborhoods, the hills and Del Mar Heights. If a leak has been found and repaired and the floor no longer feels right, request a Free Quote.