How Does Under-Slab Leak Detection Work?

The initial process for a slab leak determination when it is not obvious usually consists of a series of tests on the different parts of the water line system. We need to rule out all other leak possibilities that are far less costly to repair. That is done by isolating and narrowing the scope along with a multiple-system pressure test.

About 99% of the time, our techs are going to start by checking the potential sources of water loss that are the most likely and easiest to identify. This will usually begin with visual observations of the water meter, toilets, toilet tanks, interior faucets, water heater(s), and hose spigots. At this time, they will also take a quick assessment of any shut-offs that may be problematic for a full test to be performed.

Once the basic visual inspection is done, the next step is to isolate the irrigation system from the main line. To perform this part of the initial testing, the double-check valve must be in good working order with working shut-offs. Once the irrigation is shut off, if we still have meter movement, we proceed to the next step.

Next, the main water shut-off valve needs to be operational. This is so that we can separate and isolate everything in and under the house from the main water line that comes from the meter. This water line is commonly referred to as the “yard line.” If continued meter movement is observed after closing the main water shut-off valve, that would indicate a yard line leak and repair situation.

Even if the yard line isolation still has meter movement, we would likely still move forward with the next step in the process. That step is a complete “static pressure test” of the entire domestic water system in and under the house. Using a pressure gauge at a fully functioning hose spigot, we allow the home to fill with water. This may require us to turn shut-offs off inside the home.

Then, using the main water shut-off valve again, the house would become isolated and any drop in pressure on the gauge would indicate a leak. A true slab leak typically starts falling immediately and steadily decreases until it reaches zero.

The test is typically performed for 15-20 minutes. Sometimes, we perform it multiple times in combination with using the water heater shut-off valve to isolate the hot water lines from the cold water lines. If there is no pressure drop after performing a subsequent pressure test with the water heater shut-off valve closed, then we would assume that the leak is on a hot water line and not a cold line.