The most common slab leak signs are an unexplained jump in your water bill, the sound of running water when everything is off, a warm spot on the floor, low water pressure, a musty smell, and new cracks in floors or walls. Forbes Home lists these same symptoms, and notes that no single one proves the leak is under your slab. A pattern of two or three together is what should send you to the water meter, and then to a licensed plumber.
This guide walks through each sign, what it usually means, how to check your meter safely, what else can fool you, and what to do next if you live in Rio Rancho, Albuquerque, Corrales or anywhere else in New Mexico.
TL;DR
- Watch for a water bill that climbs with no change in your habits, running-water sounds in a quiet house, warm or damp floors, low pressure, musty odors, and new cracks.
- One sign alone is rarely proof. Two or more together justify a meter test and a call to a plumber.
- A meter test tells you water is escaping somewhere. It does not tell you where. Pinpointing a slab leak takes leak detection equipment and a trained technician.
- Other leaks (toilets, faucets, irrigation, appliances) can look just like a slab leak, so rule them out first.
- A hidden leak can damage floors, walls and the structure of the house, so do not wait to see if it goes away.
Table of Contents
- What a slab leak is and why it hides so well
- The signs, one at a time
- Quick reference: sign, likely meaning, first move
- How to run a meter test at home
- What else can look like a slab leak
- Is a slab leak an emergency?
- Does homeowners insurance cover a slab leak?
- New Mexico factors worth knowing
- How a plumber finds and fixes a slab leak
- Our perspective: why we start with a conversation
- When to call us
- FAQ
- Sources
What a slab leak is and why it hides so well
Most homes in our part of New Mexico sit on a concrete slab. Depending on how the house was plumbed, water lines, drain lines or both can run in or beneath that slab. A slab leak is a leak in one of those lines. You cannot see the pipe, so the leak does its work quietly, and the first clue is often something that looks unrelated, like a bill or a warm floor.
How long a leak can go unnoticed depends on its size, its location, the soil, your flooring and how much water the household uses. Forbes reports that slab leaks can continue for years without being noticed. A slow, small leak can hide far longer than a bigger one that quickly shows up as a bill spike, a hot floor or visible moisture.
Possible causes include shifting soil, poor installation, acidic or hard water, and older homes with copper pipes, according to the same Forbes overview of slab leak causes. Hard water is a daily fact of life here, which is one reason we pay attention to what is in the water as well as the pipes carrying it.
The signs, one at a time
1. A water bill that rises for no reason
This is usually the first clue. If your habits have not changed (no guests, no new irrigation schedule, no filled pool) and the bill still climbs, water is going somewhere. Pull your last several bills and compare the same season year over year, because summer watering naturally lifts usage here.
If you are an Albuquerque or Bernalillo County water customer, HomeConnect from the Water Authority lets customers with advanced meters see hour-by-hour or daily use and look for unusual spikes that suggest a plumbing, toilet or irrigation leak. You sign in with your Water Authority account number. Use of water at 3 a.m., when nobody is awake, is a strong hint that something is leaking.
2. The sound of running water when everything is off
Stand in the quietest room of the house, with the dishwasher, washer and ice maker idle. A faint hiss, trickle or rushing sound that you cannot trace to a fixture is worth taking seriously. Put your ear near the floor and walls close to where water lines enter the house. SERVPRO's list of warning signs also includes running-water sounds, along with bill increases and reduced pressure.
3. Warm or hot spots on the floor
A patch of floor that feels warm underfoot, especially in a house with no in-floor heat, can point to a leaking hot water line. You may notice it barefoot in the kitchen or hallway, or notice your water heater seems to run constantly because it keeps heating water that is leaking away.
Be careful with the other side of this: homes with hydronic or radiant floor heat naturally have warm floors. If that is your house, the clue is a warm spot in the wrong place or one that stays warm when the heat is off.
4. Damp flooring, pooling water or a wet carpet edge
Moisture rising through the slab can darken carpet, lift laminate, cup hardwood or leave tile grout damp. Forbes warns that slab leaks can damage walls, hardwood, carpeting and drywall. If you pull back a corner of carpet and find the pad or tack strip wet with no explanation, treat that as a strong sign.
5. Low water pressure
If pressure drops at every faucet and shower rather than at a single fixture, a leak in a main line is one possible reason. A single weak faucet usually points to a clogged aerator or a worn cartridge instead. Whole-house pressure changes deserve a closer look.
6. Musty odors or visible mold
A persistent damp smell in a room with no obvious moisture source, especially near baseboards or in a closet, can mean water is sitting under the flooring. SERVPRO notes that lingering moisture can invite mold and damage floors, walls and structure. Mold on baseboards or the lower part of drywall deserves attention even if the rest of the room looks fine.
7. New cracks in floors, walls or tile
Cracked tile, gaps along baseboards, or hairline cracks that appear in walls can be linked to water undermining the soil under a slab. Houses also settle and crack for plenty of other reasons, so cracks are a signal to investigate, not a diagnosis.
8. Changes outside the house
Forbes also mentions uneven lawn growth among the possible signs. A soggy or unusually green strip of yard near the foundation, in a place you do not water, deserves a look.
Quick reference: sign, likely meaning, first move
| Sign | What it may mean | What to do first |
|---|---|---|
| Higher water bill, same habits | Water escaping somewhere | Compare bills, run a meter test |
| Running-water sound with all fixtures off | Pressurized line leaking | Check toilets and outdoor taps, then test the meter |
| Warm spot on the floor | Hot water line leak (or radiant heat) | Note the location, check whether heat is on |
| Damp carpet, lifting floor | Moisture rising through slab | Document it and call a plumber |
| Low pressure at every fixture | Main line leak, or a supply issue | Check the main valve is fully open, test the meter |
| Musty smell, mold | Hidden moisture | Find the source before cleaning |
| New cracks | Soil movement, possibly from leaking water | Photograph and monitor, then call |
How to run a meter test at home
This is the safest first check and it costs nothing. The principle is simple: if no water is being used and the meter still moves, water is escaping.
- Shut off all water use. Turn off irrigation, the ice maker, the dishwasher and washing machine, and make sure no one flushes or runs a tap.
- Find your meter and open the lid carefully. Look for the leak indicator (often a small triangle or dial) or the sweep hand.
- Watch for movement. Portland Water Bureau's guidance says to check the indicator and, if the meter looks still, wait several hours and check again. The City of Chandler suggests waiting 10 minutes when the dial is initially still to catch a slow leak.
- Be patient with small leaks. Albuquerque Municipal Utility guidance warns that minor leaks may not register immediately and recommends comparing readings again after one to two hours without water use.
- Close the home's main shut-off valve and look again. According to that same Albuquerque guidance, continued movement points toward the line between the meter and the house, while the meter stopping points to a leak inside the house.
A moving meter confirms a leak. It does not say whether the leak is in the slab, in a wall, at a toilet or in the yard. Portland's water bureau makes the same point: a meter can help detect a leak, and a professional leak detection company can pinpoint its exact location.
What else can look like a slab leak
Before you assume the worst, rule out the cheaper explanations. Portland Water Bureau lists leaking toilets, faucets, appliances and garden hoses as common sources of meter movement. In practice we see these often:
- A running toilet. Drop a little food coloring in the tank and see whether color seeps into the bowl without flushing.
- A dripping faucet or hose bib. Small drips add up over a month.
- A leaking water heater. Water at the base of the tank or from the relief valve can raise your bill and dampen the floor. Our guide to finding a water heater leak covers the checks.
- Irrigation or a buried line outside. If the meter keeps moving after the main valve is shut, the problem is between the meter and the house.
- A sewer or drain problem. Odors and damp spots can come from drain lines instead of supply lines. See our sewer line clog checklist for those signs.
- Humidity and condensation. Musty smells in a closed-up house are not always plumbing.
If you have eliminated all of these and the meter still moves, the odds shift toward a leak you cannot see.
Is a slab leak an emergency?
It depends on what you are seeing. Treat it as urgent if you have water pooling on the floor, a floor that is hot to the touch, a meter spinning fast with everything off, or wet drywall and carpet spreading. In those cases, close the main shut-off valve, which stops the water at the source, and call a plumber. Our burst pipe emergency guide explains how to limit the damage in the first hour.
If the only sign is a modest bill increase and a slowly moving meter, it is less of a same-night emergency but it is still not something to wait on for months. SERVPRO says prompt professional repair can limit damage from hidden under-slab leaks, and the longer water sits, the more likely it is to reach flooring, walls and structure.
If water has already reached your floors, you may need to deal with the surface as well. This overview of the signs you need floor restoration helps you judge when damaged flooring needs more than a cleaning. Fix the leak first, then restore the floor, or the water will undo the work.
Does homeowners insurance cover a slab leak?
Coverage varies by policy and insurer, so we will not promise an answer. What we can say as plumbers is that documentation helps any claim: keep your water bills, take dated photos of damage, save the meter readings from your test, and ask for a written leak detection report. Call your insurance agent early and ask specifically how your policy treats hidden plumbing leaks and the cost of accessing the pipe.
New Mexico factors worth knowing
Know your meter and your utility tools. If you are in Albuquerque or Bernalillo County, HomeConnect can show you daily consumption and make leaks easier to catch. Outside the Water Authority's area, including parts of Rio Rancho, check with your own utility about what online usage tools they offer.
Leaks are your responsibility to stop. The Water Authority says water waste in its service area includes leaks and equipment malfunctions, and that customers must shut off malfunctioning equipment if repair will take longer than 48 hours. That is one more reason not to let a suspected leak linger.
Hard water is hard on pipes. Forbes lists acidic or hard water among possible slab leak causes. If your fixtures have heavy scale, it is worth testing your water. Our article on testing water first for hard water stains is a good starting point, and water softening and filtration are services we install.
What was done before the concrete was poured. New Mexico's residential permit guide requires an inspection after in-slab or under-floor piping is installed but before concrete or floor sheathing is placed. If you are buying or building, ask for the permit records, because that inspection is one of the checks protecting you from a bad under-slab install.
How a plumber finds and fixes a slab leak
Once you know water is escaping and you suspect the slab, the work moves from guessing to locating. A technician uses specialized leak detection methods to find the exact spot so the repair can be small instead of a large, messy dig. Our post on leak detection methods and how they are tested explains what the tools do.
After the leak is located, the options generally fall into three groups:
- Spot repair at the leak, which may involve opening the floor above it.
- Rerouting the affected line through walls or the attic so it no longer runs under the slab.
- Repiping when the pipes are failing in more than one place. If that sounds like your house, read our whole house repipe checklist.
Which option fits depends on the age and material of your pipes, the number of leaks and how the house is laid out. A good plumber will show you what was found and explain the choices before work starts, not after.
Our perspective: why we start with a conversation
We have been plumbing New Mexico homes for more than 38 years, and slab leaks are rarely the first thing a homeowner calls about. They call about a high bill, a warm patch by the hallway, or a smell they cannot place. By the time someone says "slab leak," they have usually spent weeks worried and searching.
So we start by listening. When you call us, you reach a local person, not an automated menu, and we ask what you have noticed. Often we can tell you what to check first: the meter, the toilets, the water heater. Sometimes a phone call saves you a service visit. Other times it confirms that you need leak detection right away.
Our advice is the same whether the house is in Corrales, Rio Rancho or Albuquerque: do not guess where the water is going, and do not tear up a floor until the leak has been properly located. When we work in your home we leave it clean, because a repair is only finished when you cannot tell we were there.
— Aaron Waller, General Manager
When to call us
If your meter keeps moving with everything off, if you have a warm spot or a damp floor, or if you have two or more of the signs above, it is time to bring in a licensed professional. Waller's Plumbing and Heating handles plumbing repairs, leak detection, re-piping and water heater service for homeowners across New Mexico. Tell us what you have seen and what your meter did, and we will help you decide the next step. You can also start from our home page to book an appointment.
FAQ
How long can a slab leak go undetected?
Potentially for years. Forbes notes that the time depends on leak size, location, soil, flooring and household water use. A quiet leak can stay hidden much longer than one that quickly shows up as a bill spike, warm floor or pressure drop.
Is a slab leak a big deal?
Yes, because it is hidden and keeps getting worse while you are not looking. Lingering moisture can damage floors, walls and structure and invite mold. Catching it early usually keeps the repair smaller and the damage limited.
Is a slab leak an emergency?
It is urgent when water is pooling, a floor is hot, or your meter is moving quickly with everything off. Close your main shut-off valve and call a plumber. If the signs are mild, schedule leak detection soon rather than waiting.
How do I detect a slab leak myself?
Run a meter test: turn off all water use, check the leak indicator or sweep hand, and compare readings after an hour or two. If the meter moves, close your main valve and check again to learn whether the leak is inside the house or between the meter and the house. The test confirms a leak but cannot locate it, so a plumber with detection equipment is the next step.
Sources
- Slab Leak: Signs You Need A Plumber, Forbes Home
- Slab Leak Repair: Signs, Risks & Repair Options, SERVPRO
- How to check for leaks, Portland.gov
- Check for Water Leaks, City of Chandler
- Leak Diagnosis Guidance, Albuquerque Municipal Utility
- HomeConnect, Albuquerque Bernalillo County Water Utility Authority
- Water Waste Overview and Enforcement, Albuquerque Bernalillo County Water Utility Authority
- Building Permit Guide for Residential Construction, New Mexico
- 7 Clear Signs You Need Floor Restoration at Home