When you need a hydrostatic test
- You are buying or selling an older home with cast iron drains and the inspector has recommended one.
- A structural engineer is evaluating settlement or cracking and needs to rule drain leaks in or out.
- An insurance claim for a drain leak requires confirmation.
- A sewer odor or pests keep appearing with no visible cause.
- You are about to remodel a bathroom or kitchen, or install new flooring over the slab.
- The house has had a sewage backup and you need to know whether the drains were damaged.
Pass, fail and what a failed test means
If the water level holds for the test period, the under-slab drains are holding water and the test passes. If the level drops, the system has a leak, and how fast it drops gives an indication of how large the leak is.
A failed test is followed by isolation: we test each branch, such as a bathroom group or the kitchen line, separately to find the one that leaks. A camera inspection then shows the defect and its location. Repair options include replacing the failed section, lining the pipe, or replacing the under-slab drains, and they are explained on our sewer line repair and foundation leak repair pages.
How the test works
Access the cleanout
We locate the main cleanout where the drain system leaves the house.
Seal the system
An inflatable test plug is set in the line to close the drains off from the sewer.
Fill to floor level
The drain lines are filled with water until it reaches the level of the lowest fixture opening.
Monitor the level
We watch the water level for a set period and record any drop.
Isolate a failed branch
If the level drops, branches are tested one by one to find the leak.
Camera and report
A camera inspection shows the defect, and you receive a written report of the results.
Hydrostatic testing and pressure testing are different tests
A hydrostatic test checks the drain system, which is not under pressure and only carries water when a fixture is used. A pressure test checks the water supply lines, which are pressurized at all times. A house can pass one and fail the other, so the test has to match the system in question. Supply line testing is part of water leak detection.
What to expect on test day
No water can go down any drain during the test, so plan for the house to be without toilets, showers and sinks for the length of the visit. To watch the water level, we usually remove a toilet on the lowest floor and reset it afterwards with a new wax ring. The complete visit, including isolation of any failed branch, usually takes a few hours.
Hydrostatic Plumbing Testing questions
Can a hydrostatic test damage my plumbing?
The test fills drains only to floor level, which is the same height water reaches when a drain backs up during normal use. Pipe that fails the test was already leaking. We monitor every fixture during the test so water does not overflow.
Is a hydrostatic test required to buy a house?
It is not required by law. Home inspectors, lenders and structural engineers often recommend it for older homes on slabs, especially those with cast iron drains.
Can a condominium unit be tested?
Yes, ground floor units on a slab can be tested. Shared lines usually need coordination with the association, since the test briefly takes the connected drains out of use.
When will I know the results?
During the same visit. You receive a written report of whether the system held water and, if it did not, where the failed branch is.