I Need a Hydrostatic Test — What Is It and Do I Really Need One?

A hydrostatic test is a pressure test of your home’s under-slab drain lines — the plumbing that runs beneath your concrete foundation. The test works by temporarily plugging your drain system and filling it with water to check whether it holds pressure. If the water level drops, there’s a leak somewhere in the line beneath your slab.

It sounds simple because it is. But what it reveals can completely change the scope — and the cost — of a foundation repair project.

Why It Matters Before Foundation Repair

Here’s something that surprises many homeowners: a sewer line leak beneath your slab can cause the exact same symptoms as foundation settlement — uneven floors, sticking doors, cracks in brick and sheetrock. The two problems look identical from the surface. If a foundation contractor repairs your piers without first identifying an active plumbing leak, the leak continues eroding soil beneath the slab, and the foundation moves again. The repair fails — not because the pilings were wrong, but because the underlying cause was never addressed.

A hydrostatic test before foundation repair tells us:

• Whether an active plumbing leak exists beneath your slab — and is contributing to or causing your foundation symptoms
• Whether foundation repair alone will solve the problem — or whether sewer line work needs to happen first or simultaneously
• Where the leak is located — through follow-up isolation testing that pinpoints the exact section of pipe that has failed
• Whether your existing drain lines are structurally sound — important context before any pilings are installed near or beneath them