What Are the Signs of a Slab Leak?
If your water meter leak indicator spins with every fixture and appliance off, you have a slab leak. Call 602-560-8989 for slab leak detection. Otherwise the signs are subtle: a water bill creeping up, a warm spot on tile in summer, or running water in a quiet house.
The cheapest test you can run is at your water meter. With every fixture and appliance off, watch the small leak indicator dial. Any movement means water is moving when it should not be. Most slab leak detection calls we run start with that test failing.
Slab leaks show up faster in Phoenix than most metros. Expansive soils heave during monsoon, old copper corrodes from inside out, and post-tensioned slabs need a cable scan before any slab cutting. Call 602-560-8989 before damage compounds.
Common Causes
Unexplained Increase in Water Bill
A pinhole in a 3/4-inch copper supply line under your slab can waste 1,500 to 3,000 gallons a month. That happens before you ever see standing water. If your bill jumps 20-30% with no usage change, assume a leak until you have ruled it out.
Sound of Running Water
With every fixture off, the house should be quiet. A constant hissing, faint splashing, or running-water sound from a floor or wall is almost always a slab leak. Put your ear to the tile floor; the loudest spot is usually within 5 feet of the actual leak.
Warm or Damp Spots on Floors
Hot-water-line slab leaks heat the concrete or tile above them. Walk barefoot across tile floors in summer with the AC running; a warm patch in an otherwise cool slab is one of the strongest signals. Pets pick up on warm spots faster than people do, so a new favorite napping spot on tile is worth checking.
Cracks in Walls, Floors, or Foundation
Water from a slab leak erodes soil under your foundation. In Phoenix expansive caliche and clay, the slab settles, and you get diagonal cracks at door frames or fresh exterior cracks. Photograph and date suspicious cracks; if they widen over a few weeks, soil is moving from a leak underneath.
Mold, Mildew, or Musty Odors
Constant slab moisture builds mold in materials above before you see anything visible. You will smell mildew first, especially in closets, behind furniture against an exterior wall, or near baseboards. Phoenix dry indoor air normally holds back mold, so a persistent musty odor means moisture is coming from inside a wall or under flooring.
Low Water Pressure Throughout House
A significant slab leak diverts water before it reaches your fixtures and drops pressure house-wide. If pressure is weak everywhere and a hose-bib gauge reads under 40 PSI, run slab leak detection before replacing a PRV. The new PRV does nothing if the real cause is a slab leak.
Water Heater Running Constantly
A hot-side slab leak means your water heater is making hot water it never delivers. Listen for the gas burner cycling every 30 to 45 minutes when no one is using hot water. Your gas or electric bill jumps at the same time as your water bill, which is the dual-utility signal of a hot-line slab leak.
What Should You Do?
Try This First
- Find your water meter (usually a concrete box near the curb with a green or black lid). Lift the lid and locate the small triangular or star-shaped leak indicator next to the main dial.
- Shut off every fixture and appliance: toilets fully refilled, ice maker off, irrigation off, dishwasher and washer not running. Watch the leak indicator. Any spin at all means water is moving somewhere it should not.
- If the leak indicator spins, shut the main water valve to the house. If the indicator stops, the leak is inside the house. If it keeps spinning, the leak is in the service line between the meter and the house.
- Walk barefoot across every tile and concrete floor, especially in summer with the AC running. Note warm or damp spots, and watch where pets lie down. A new favorite cool-tile spot often sits above a hot-line leak.
- Listen near baseboards and walls in a quiet house (early morning works best). A persistent hissing or running-water sound that you cannot trace to a fixture is a strong slab leak indicator.
- Compare your last three water bills against the same three months a year ago. A 20% or higher jump with no usage change is a leak signal worth investigating.
- Walk the foundation exterior and check for new cracks, especially horizontal cracks or cracks near corners. Photograph and date any you find; if they widen over a few weeks, soil is moving underneath from a leak.
Call a Pro If...
- Water meter leak indicator spins with every fixture and appliance off (immediate slab leak detection call, no DIY beyond this point)
- Multiple slab leak signs are present at the same time (warm spots plus bill spike, or running-water sound plus new cracks)
- Hot water heater cycles every 30 to 45 minutes with no hot water in use (hot-line slab leak doubles your gas or electric bill)
- New diagonal cracks at door frames or baseboard-to-floor gaps that open over a week or two (active soil movement, foundation damage compounds quickly)
- You smell mold but cannot find a visible source (slab leaks under flooring are the most common hidden moisture source in Phoenix homes)
- Post-1965 slab-on-grade home with original copper supply lines and any sign above (50+ years in Phoenix hard water is past design life for copper)
- Post-tensioned slab home (common in Phoenix homes built 1980 and later); slab cutting requires an engineer's review, so call before anyone breaks ground
- Your insurance carrier needs leak-source confirmation for a damage claim (most policies cover the damage but not the line itself)