Using Gravity to Find a Leak

There are so many tools in a leak detectors box that can be used to locate a leak, but one tool that is often overlooked is water column pressure.

Columbus Georgia and Phenix City Alabama sit on the fall line, a geographic feature that separates the coastal plain from The Piedmont. Essentially everything south of the fall line is relatively flat, with sand and clay being the primary soil. Everything north is limestone, granite, and other rocks.

Water service north of the fall line can easily be five hundred foot runs with multiple terrain changes. The ground can be porous limestone and consistently act as a natural French drain. In other words, no ground sign of a leak.

Finding a leak in such conditions can be frustrating, to say the least. A homeowner knows they have a leak because the meter clocks, but can't find it because there is no indicator of where it could be. Using a listening device on a five hundred foot water un can be tedious and cost prohibitive, since most leak detection services charge by the hour.

These leaks are the perfect opportunity for using pressure to determine approximate leak location.

First, the leak can't be an intermittent one, that is it can't be a thermal expansion leak or a fitting that only leaks above x psi. Second, there has to be a little bit of altitude associated with the leak. In Georgia and Alabama thats easy, as the houses with the long water services are always next to a water feature, so they are downhill of a meter.

The steps to conducting this are easy. Like every leak, isolate the house by sealing the whole house shutoff, or closing the toilet compression stops and ensuring no water is running. Then put a pressure gauge on the exterior hose bib. Obviously, the hose bib being used needs to still have water flow to it. Turn off the meter at the street. The line is now isolated between the pressure gauge and the meter. Wait about ten minutes, and find the residual pressure in the line by noting the pressure gauge.

Let's say for example the pressure gauge reads 18 PSI. We would know that the line has 18 pounds of water column remaining in the line. Each pound of water equates to 27.7 inches of water column.

Simple math says 18*27.7=498. 498/12=41.5 feet. Add the height of the hose bib, which is generally about 2 feet, and you get 43.5 feet of water column on the line. The leak will be approximately 43.5 feet above the slab of the house.

Keep in mind, that isn't 43.5 feet away from the house, it is in vertical distance only. So if the water service is on a gradual slope, the leak could be a full five hundred feet away. If the water service runs down a steep driveway, then the leak could be much closer.

Once you have the approximate location based on altitude, then you could easily run your normal leak detection at a good starting point.

Some caveats to this method are important to note. If the leak is large, back siphonage can pull water uphill. That means that the pressure/altitude reading could be as much as 33 feet off, the maximum a vacuum can pull water. Most likely, however, back siphonage would only pull a few feet. So if you have no luck finding the leak at the level, go uphill, not down.