How to Tell If You Have a Slab Leak
A leak in the pipes beneath your concrete slab can quietly waste water and damage your foundation for months. Here are the warning signs — and a simple test you can do today.
Quick Answer
The most common signs of a slab leak are an unexplained spike in your water bill, the sound of running water when everything is off, a warm spot on the floor, low water pressure, and unexplained moisture or cracks in the slab. The fastest way to confirm one at home is the meter test: shut off all water and watch whether the meter keeps moving. If it does, you likely have a hidden leak.
What is a slab leak?
A slab leak is a leak in one of the water lines that run underneath — or embedded within — the concrete foundation slab your home sits on. Because the pipes are buried in or below concrete, the leak is hidden from view and can go undetected for a long time, all while losing water and undermining the soil and foundation. Many Citrus County homes are built on concrete slabs, which makes this a problem worth knowing the signs of.
The 5 warning signs
Water bill spike
A sudden, unexplained jump in your bill with no change in usage is the classic early sign.
Sound of running water
Hearing water move through pipes when every faucet and fixture is off points to a hidden leak.
Warm spot on the floor
If the leak is on a hot-water line, you may feel a warm patch on the floor above it.
Low water pressure
A leak diverts water before it reaches your fixtures, so pressure drops throughout the home.
Moisture or cracks in the slab
Damp flooring, warped wood, mildew smell, or new cracks can signal water pushing up from below.
The do-it-yourself isolation test
If your home is on a water meter, you can narrow down whether you have a leak — and roughly where it is — in under an hour:
Turn off all water & check the meter
Shut off every faucet, appliance, ice maker, and irrigation system, then watch your meter. If it's still moving with everything off, water is escaping somewhere.
Locate your main house shut-off valve
Find the shut-off valve where the water line enters the house. Knowing where this is also lets you stop water fast in a real emergency.
Shut off the house valve & recheck the meter
If the meter stops, the leak is inside the house — often a line under the slab. If the meter keeps running, the leak is isolated to between the meter and the shut-off valve — an outside (yard line) leak.
Isolate the hot-water line
Shut the valve at the water heater and watch the meter again. If it stops, the leak is on the hot-water line. This step also buys you time — you can stop the leak while keeping cold water running to the house.
On a private well? Watch your pump.
Many Citrus County homes are on a well and have no meter to read — so the well pump becomes your indicator. With every fixture off, the system should hold pressure and stay quiet. A hidden leak forces the pump to keep replacing lost water. Watch for:
- Constant running of the well pump, or a pressure switch that clicks on and off (short-cycles) when no water is being used
- The pump kicking on by itself overnight or while you're away
Before blaming a slab leak, rule out a waterlogged pressure tank or a failing pressure switch — both can cause a pump to cycle constantly on their own. If the tank and switch check out and the pump still won't rest, you likely have a leak in the lines, which can include a slab leak. We can test all three.
Don't wait on a confirmed slab leak. Left alone could lead to more expensive repairs such as a burnt out well pump or well equipment, high water bills, higher electric bills, or water heater repairs from abnormal usage. Early detection means a smaller, less expensive repair.
$95 Slab Leak Diagnostic
$95Modern Plumbing offers a flat $95 slab leak diagnostic to help determine if professional leak detection is needed. We will have a professional plumber go through and check all plumbing fixtures and run our slab leak diagnostics to see if Professional Leak Detection is needed. If needed, we will refer you to American Leak Detection. You can also follow the Self Diagnostic steps above to determine if you need professional leak detection. If repairs are needed, we provide free estimates on all slab leak repairs — so you know your options before any work begins.
Proudly partnered with American Leak Detection for professional leak detectionHow a professional pinpoints the leak
Confirming a leak is one thing; finding its exact location under concrete without tearing up the whole floor is another. Through our partnership with American Leak Detection, we use professional electronic leak detection equipment to pinpoint the spot, then repair it with the least invasive method possible — whether that's a spot repair, a reroute, or a section of repipe. See our slab leak repair page for details.
Slabs, soil & Citrus County
A large share of Citrus County homes are built on concrete slabs, and our region's sandy, karst-influenced ground can shift around a persistent leak. Catching a slab leak early here isn't just about the water bill — it's about protecting your foundation. We've been locating and repairing leaks across Inverness, Crystal River, Homosassa, and Lecanto since 1978.
Frequently asked questions
What are the first signs of a slab leak?
The earliest signs are usually an unexplained increase in your water bill and the sound of running water when all fixtures are off. A warm spot on the floor, dropping water pressure, and damp or cracked flooring are also common indicators.
How can I check for a slab leak myself?
Turn off all water in the home and check your meter — if it's still moving, water is escaping. Then shut off the main valve where the line enters the house and recheck: if the meter stops, the leak is inside (often under the slab); if it keeps running, the leak is outside between the meter and the valve. Shutting the valve at the water heater can further isolate the leak to the hot-water line.
How do I check for a slab leak on a private well with no meter?
On a well, watch the pump instead of a meter. With every fixture off, the pump should stay quiet and hold pressure. If the pump runs constantly or the pressure switch keeps clicking on and off with no water in use, you may have a leak. First rule out a waterlogged pressure tank or a failing pressure switch, since both can cause a pump to cycle on their own — if those check out, a line or slab leak is likely.
How much does slab leak detection cost?
Modern Plumbing offers a flat $95 slab leak pre-diagnostic to help determine whether professional leak detection is needed, and we provide free estimates on all slab leak repairs. We proudly partner with American Leak Detection for professional, precise leak location, which normally costs around $350.
Is a slab leak an emergency?
It should be treated as urgent. While it may not flood your home immediately, a slab leak wastes water continuously and can erode the soil supporting your foundation, leading to costly structural damage. The sooner it's located and repaired, the smaller the problem.
Can a slab leak be fixed without breaking up my whole floor?
Often, yes. Once the leak is pinpointed by American Leak Detection they will mark a section on your floor or in the area found. Leak Detection helps precisely locate the area of the leak for the least amount of concrete and flooring repairs. Learn about our slab leak repair.
Think you have a slab leak?
We'll locate it precisely and recommend the least invasive repair — honest pricing, no commission. $95 slab leak pre-diagnostic, and free estimates on all slab leak repairs.
Modern Plumbing, Inc. · Family-owned since 1978 · FL License #CFC1431599 · 4196 S. Pleasant Grove Rd, Inverness, FL 34452
