A hydrostatic plumbing test is the fastest way to find out if the drain and sewer lines under your slab are leaking. The plumber plugs the main cleanout, fills the system with water, and watches the level for 15 to 20 minutes. If the water drops, there is a leak under the house. In Dallas-Fort Worth, where most homes sit on a slab over expansive clay, this one test answers a question that is otherwise hidden under four inches of concrete.
In short
- The test checks the sewer and drain lines under the slab, not the pressurized supply. A plumber plugs the cleanout, fills the pipes, and watches for 15 to 20 minutes.
- DFW clay soil swells when wet and shrinks when dry, which moves the slab and cracks or separates the drain lines under it.
- Get one when buying or selling, before and after foundation repair, after repeat sewer backups, or in a home built before 1980 with cast iron drains.
- A visit takes about 1 to 2 hours. A failed test leads to a camera inspection and isolation test. Repair pricing is quoted after inspection.
What a hydrostatic plumbing test checks
A hydrostatic plumbing test covers the drain side of your plumbing, not the pressurized supply. An intact drain line holds a column of water indefinitely. A line with a crack, a separated joint, or a rusted-through section lets that water seep into the soil, and the level in the cleanout drops.
The hydrostatic inspection service at The Right Choice fills the system with water, identifies leaks and weak points, and gives you a report with recommendations. For the pressurized side, a slab leak inspection covers the supply lines with different tools.
Why DFW slab homes need a hydrostatic plumbing test
Most homes in Dallas, Fort Worth, Arlington, Plano, and Frisco are built slab-on-grade, with the drain lines buried under the concrete. North Texas sits on expansive clay. Research from the Texas A&M Transportation Institute describes how these clays swell when they take on water and shrink when they dry. Between a wet spring and a dry August, the soil under a DFW home can move enough to lift and drop the slab by more than an inch.
The pipes move with it. PVC joints pull apart and older cast iron cracks. The leak can run for years with no visible sign inside the house. The EPA WaterSense program reports that about 10 percent of homes have leaks wasting 90 gallons a day or more. Under a slab, a leak that size can go unnoticed for a long time.
When to schedule the test
- Buying or selling a home. A standard home inspection does not include it. Most DFW buyers add one on homes older than 20 years. See our guide to plumbing inspections before buying or selling.
- Before and after foundation repair. Lifting a slab can separate drain joints. Test before to document the starting condition, and again after the piers are set.
- Slab leak signs. Damp floors, a mildew smell, or new cracks wider than 1/8 inch. The full list is in our post on slab leak signs in DFW homes.
- Recurring sewer backups. If a line needs drain cleaning more than once a year, a break or a belly in the pipe is usually why.
- Homes built before 1980. Cast iron drains from that era are 45 years old or more and often rusted through.
Hydrostatic plumbing test step by step
- Locate the main cleanout. Usually a capped fitting in the yard near the foundation. If needed, read how to find your sewer line cleanout.
- Seal the line to the street. An inflatable test ball is placed in the cleanout and inflated, which isolates the piping under the house from the city sewer.
- Fill the system. Water is run into the drain lines until it reaches the lowest fixture, typically a shower or floor drain.
- Watch the level. The plumber marks the water level and waits 15 to 20 minutes. A line that holds has passed. A level that drops means water is leaving the pipe under the slab.
- Drain and release. The plug is deflated, the water flows out to the sewer, and the cap goes back on.
Plan on about 1 to 2 hours. Nothing is cut or dug. Just do not run drains while the test is in progress.
What a failed hydrostatic plumbing test means
A drop in the water level confirms a leak but not where. Two more steps narrow it down.
Camera inspection
A sewer camera goes in through the cleanout. The plumber watches for cracks, offset joints, roots, and sags, and a locator on the camera head marks the spot on the floor above.
Isolation testing
If the camera cannot find the break, the plumber plugs sections of the system one at a time and refills each. The section that loses water contains the leak.
Repair options
- Spot repair. One bad joint under a floor you can open. Cut the concrete, replace the section, patch the slab.
- Reroute. If the break sits under a kitchen or a finished floor, a new line around it can cost less than opening the slab.
- Tunneling. Crews dig under the foundation from outside, replace the pipe, and backfill. Common for cast iron in older DFW homes.
Our sewer line repair team quotes after the camera and isolation work, once location and pipe material are known.
Hydrostatic test vs camera inspection vs isolation test
| Test | What it answers | How it works | Time |
|---|---|---|---|
| Hydrostatic plumbing test | Is there a leak under the slab? | Plug the cleanout, fill the drains, watch the level 15 to 20 minutes | About 1 to 2 hours |
| Camera inspection | Where is the damage and what does it look like? | Push a camera through the lines and locate problems from above | About 1 hour |
| Isolation test | Which section is leaking? | Plug and refill one branch at a time | 1 to 3 hours |
They are usually done in that order: the hydrostatic plumbing test confirms the leak, the camera shows the pipe, and isolation pins down the section.
Hydrostatic plumbing test FAQ
Does a hydrostatic test damage the pipes?
No. The drains are filled only to the height of the lowest fixture, a few feet of water column, far below what the pipe handles in normal use. A line that fails was already leaking.
Is it part of a regular home inspection?
Usually not. A general inspector runs the fixtures and looks for visible leaks. The hydrostatic plumbing test is a separate plumbing service that most DFW buyers add on slab homes older than 20 years.
How much does a hydrostatic test cost?
The test is a fixed-scope visit of about 1 to 2 hours. The Right Choice quotes it after reviewing your home, and any repair is quoted only after the camera and isolation work.
What if the test passes but I still have slab leak signs?
The leak may be on the pressurized supply side, which this test does not cover. A slab leak inspection uses electronic listening equipment and meter checks for supply lines.
Schedule a hydrostatic test in DFW
The Right Choice Heating and Air runs hydrostatic tests, camera inspections, and residential plumbing repairs across Dallas, Fort Worth, Arlington, Plano, Frisco, Carrollton, Farmers Branch, Irving, and nearby. Call (214) 251-4015 or schedule an appointment online. The EPA puts household leaks near 10,000 gallons a year per home, and the ones under a slab are the easiest to miss.