Many Florida homes sit on a concrete slab, with water lines running beneath the floor instead of in a crawlspace. When one of those lines fails, you won’t see a puddle under the sink. You’ll see the signs of a slab leak instead: a strange water bill, a warm floor, a sound you can’t place.
This guide walks through the warning signs I look for, a water meter test you can run yourself, how we find the leak and what drives slab leak repair cost.
What are the most common signs of a slab leak?
The most common signs of a slab leak are an unexplained jump in your water bill, warm or hot spots on the floor, the sound of running water when every fixture is off, damp or discolored flooring, a musty smell and new cracks in floors or walls. In my experience, the high water bill is often the first clue. None of these proves a leak alone, but two or more together deserve a closer look. The EPA’s WaterSense program says the average household’s leaks can account for more than 9,300 gallons of water wasted every year, and a slab leak can hide far more.
Hot water lines tend to announce themselves with warmth, while cold water leaks are quieter and often show up only on the bill. Where you see water isn’t necessarily where the pipe is leaking. Water travels under a slab and through building materials, so I don’t open a floor just because that’s where the wet spot is.
Where you see water isn’t necessarily where the pipe is leaking.
Use this checklist to sort out what you’re seeing:
| Sign | What it can mean | Quick check |
|---|---|---|
| Water bill jumps with no change in use | Water escaping somewhere in the system | Run the water meter test below |
| Warm or hot spot on tile or wood | A hot water line leaking under the slab | Walk the floor barefoot; note if the spot spreads |
| Sound of running water with everything off | Pressurized water escaping | Listen near floors and walls at a quiet time of day |
| Damp carpet or lifting flooring, no obvious source | Water wicking up through the slab | Rule out appliances, AC drains and plumbing fixtures |
| Musty or mildew smell at floor level | Ongoing moisture under flooring | Check baseboards and carpet edges |
| New cracks in floors or walls | Possible soil movement under the slab | Photograph and date them to track changes |
| Water heater running constantly | Hot water line losing water | Listen for the burner or elements cycling when no one is using hot water |
Which homes are most likely to have a slab leak?
I see slab leaks most in homes where the water piping runs through or under the slab, especially older homes with copper. Copper can develop pinhole leaks as it ages. Homes piped through the attic are a different situation, so I identify how the lines are routed before assuming anything is under the slab. In slab-on-grade homes across Jacksonville, the floor is often the first place the problem shows.
How do you do a water meter test for a slab leak?
A water meter test is the simplest way to confirm a hidden leak, and it takes one to two hours. First, turn off every fixture and water-using appliance in the house, including the ice maker, washing machine, dishwasher and irrigation system. Then find your water meter, usually in a box near the street, and write down the reading. Many meters have a small leak indicator, often a triangle or dial, that spins when any water is flowing.
If that indicator moves with everything off, or the reading changes after one to two hours without using water, water is leaving the system somewhere. That doesn’t tell you where. A running toilet or irrigation leak can cause the same result, so rule those out before assuming the slab. The EPA says fixing household leaks can save about 10 percent on water bills.
If the meter moved, you can narrow things down further:
- Close the main shutoff at the house, if you have one. If the meter keeps moving, the leak is likely on the service line between the meter and the house.
- If the meter stops, the leak is inside the house’s plumbing.
- Close the cold water valve on top of the water heater. If the meter stops then, the leak is likely on the hot water side.
Stop there and call a plumber. Opening flooring to hunt for the source rarely ends well.
Write down your readings and the times you took them. Those notes help the plumber decide where to start testing. If the meter did not move at all over two hours, a slab leak is unlikely, and the other signs may have a different cause, such as an AC condensate line or a shower pan leak.
How do plumbers find a slab leak without breaking the floor?
We find slab leaks with symptoms and instruments rather than guesswork, so the floor stays intact until we’re as close to the leak as we can reasonably get. The process usually begins with pressure isolation testing, which confirms a leak exists and shows which line is losing pressure, hot or cold. Next comes acoustic leak detection: sensitive ground microphones listen through the concrete for pressurized water escaping, and we trace that sound along the line to its loudest point. Thermal imaging adds another view, because a leaking hot water line leaves a heat signature on the floor above it.
The point of all this is to avoid blindly breaking concrete. A marked location keeps any opening small and targeted instead of exploratory. It also produces a written diagnosis you can share with your insurance agent before any repair decision is made.
Jacksonville adds a wrinkle. Homes near the St. Johns River and other low areas can have a high water table, and heavy summer storms saturate sandy soil. Moisture readings alone can mislead, which is why pressure and acoustic tests carry more weight than a damp spot.
For leaks that aren’t under the slab, like lines in walls or ceilings, general water leak detection uses many of the same tools.
What drives slab leak repair cost?
Slab leak repair cost depends mostly on where the leak is, how the pipe is routed and which repair method makes sense. A spot repair opens a small section of slab above the marked leak, fixes the pipe, pressure tests it and restores the concrete. An overhead reroute abandons the leaking line and runs a new one through the walls or attic, leaving floors untouched. A repipe replaces the failing system when one leak suggests others are coming.
I lean toward a spot repair when the leak is isolated and access is reasonable. With older under-slab piping that keeps failing, I don’t like breaking the slab every time, so we talk about a reroute or a whole-home repipe. What moves the price within each path includes the leak’s depth and location, the flooring on top, the pipe material and how much wall or ceiling a reroute opens. We quote after the leak is located, not before.
The question isn’t only “how do we repair this leak?” It’s “what are the chances we’re doing this again somewhere else?”
Gray polybutylene or heavily corroded pipe often favors replacement over a single repair. If your home was built from the late 1970s through the mid-1990s, check whether it has polybutylene supply lines. Our guide to polybutylene pipes in Jacksonville explains how to spot them.
Common slab leak mistakes
- Waiting for visible water. By the time water surfaces through a slab, it has usually been leaking for a while.
- Opening the floor where the wet spot is. Water travels under a slab, so the wet spot and the leak can be in different places. Without detection, demolition is a guess.
- Assuming every leak is under the slab. In attic-piped homes, the lines may not run through the slab at all, so find out how your water lines are routed first.
- Blaming the utility for a high bill. A bill that jumps with no change in use is one of the earliest signs, so test before disputing it.
- Skipping the irrigation check. Irrigation leaks can make the meter test look like a slab leak.
- Fixing the same line over and over. Repeated leaks on older under-slab pipe usually mean the pipe is failing along its length, and a reroute may cost less over time.
How RiverCity handles a suspected slab leak
I start with the symptoms and with how your water lines are routed, because an attic-piped house and a slab-piped house are different problems. Pressure isolation tells us whether water is escaping and which line is losing it. Then we use acoustic leak-detection equipment to narrow the location and mark it on the floor, getting as close as reasonably possible before anything is opened.
Next, I explain your repair options side by side: spot repair, reroute or repipe, and what each means for your floors and walls. If the leak is isolated, a spot repair may be all you need; if older pipe keeps failing, we talk about whether you’ll be doing this again elsewhere. You get a written, upfront quote before any work starts, along with a written diagnosis you can share with your insurance agent. Our slab leak repair page walks through each method in more detail.
RiverCity offers 24/7 emergency service from two Jacksonville locations, on the Southside and the Northside. If the meter test points to a hidden leak, start with our slab leak detection in Jacksonville.