Slab Leak vs Sewer Line Leak: How to Tell the Difference
Both can run under your floor, but they are different problems. One carries pressurized clean water and shows up on your meter. The other carries waste by gravity and shows up as drains and smells.
The basic difference
| Slab (water supply) leak | Sewer or drain line leak | |
|---|---|---|
| What leaks | Pressurized clean water | Waste water by gravity |
| Water meter | Keeps moving | Does not move because of the leak |
| Typical signs | Running sound, warm floor, bill increase, low pressure | Slow drains, gurgling, sewage smell, damp spots |
| How it is found | Pressure isolation, acoustic, thermal | Drain camera inspection |
| Repair | Spot repair, reroute, epoxy lining or repipe | Drain repair or replacement |
Signs of a sewer line problem
- Slow or repeated drain clogs in several fixtures
- Gurgling sounds from drains
- A sewage smell indoors or in the yard
- Damp or sunken areas that smell
- Mold near floors
Telling them apart
- Run the meter test. If it moves with everything off, you have a pressurized water leak. See how to tell if you have a slab leak.
- If the meter is still and you have drain or smell symptoms, ask for a camera inspection of the drain line.
- If both apply, you may have two problems. Test each.
Permits for drain repairs
The City of Pomona handout exempts stopping leaks in drain, soil, waste or vent pipe, but says that if a pipe is defective and must be replaced, the work is treated as new and needs a permit. See Pomona plumbing permits.
Which one are we talking about?
This site focuses on pressurized water supply leaks under slabs. If the symptoms point to a drain line, tell us when you call so we can say what we can and cannot help with. Start with slab leak detection.
Frequently asked questions
Can a sewer leak raise my water bill?
Usually not. A drain leak does not draw water through your meter. A pressurized leak does.
How is a sewer leak found?
Usually with a camera inspection of the drain line.
Can I have both at once?
Yes. Test the water supply with the meter and the drain with a camera inspection.
Is a sewer leak under the slab an emergency?
Sewage smells and backups should be addressed quickly. Call a plumber and avoid using fixtures that drain to the affected line.
Sources: City of Pomona plumbing permit handout (Nov 2024)
Keep reading
Need slab leak repair Pomona homeowners can book? See our slab leak repair Pomona page for how we work, or call (909) 415-2610.
Water running, or a warm spot on the floor?
Shut off the main if water is visible, then call. A Pomona plumber will tell you what to do next.
Call (909) 415-2610More on slab leaks
- Who Pays for a Slab Leak? Owner, Landlord, Tenant or HOA
- Copper Pinhole Leaks: Why They Happen and What to Do
- Floor Restoration After a Slab Leak: Patching and Finishing
- How to Prevent Slab Leaks: What Homeowners Can Do
- Slab Leak Signs by Floor Type: Tile, Wood, Carpet and Vinyl
- Browse the full slab leak guide
