How to Find a Water Leak Underground

Pretty sure you have a leak underground but can’t find it? There are a few things you can do to at least locate the area.

One of the first things to do is confirm it’s in the irrigation system. Turn the water to the system off at the backflow or isolation valve. Turn off all water in the house, including your icemaker. Find your water meter. On the meter you might see a small triangle or disk. If the triangle is spinning then water is flowing. If it is flowing while the water to the irrigation system is off then you have a leak in another area. You might want to get a plumber involved.

If you meter does not have the triangle or disk, write down the numbers. Leave the water off for about ½ hour. Come back and compare numbers. Again, if it has changed the leak is in your plumbing somewhere. If it has not we can assume the irrigation system.

Remember something before we start: water travels. Water under pressure really loves to travel. Take a look at the picture. This is an example of a real problem. The owner looked for the leak daily for over a week with no success. We found it using the probe idea discussed later in the paper.

An important fact: the water will show up somewhere. The only question is ‘where?” When looking for a leak check for signs on neighboring properties. In another example, a system had a leak along the common fence line. Because of the slope of the yards the neighbor’s yard was slightly lower at the fence line than that on the system side. The water was coming to the surface but on the wrong side of the fence and about 2 feet away in a lower area. Water always shows.

Based on these ideas, the first thing to do is just walk the property, including the perimeter. See puddles with no rain? Green grass in a dead area? Sunken ground? Soft spots, soggy spots, holes? No? Let’s check the zones. Since its best to do this with the system running you should plan on getting wet. Turn the zone on with enough time to allow you to check the area. If you don’t know which zone is leaking you will have to repeat this for each one. Any signs of water running down the street? We are looking for bubbling water, seeping water, and, of course, flowing water.

Another thing to look for is undercutting. Check around the edges of the sidewalk, drive and house foundation and look for soil washout. This could be an indication that the leak is either right next to or under the slap. If it is under the slab you should get a professional involved.

If there is still no sign of a leak it’s time to use a probe. Find a long piece of steel bar. A soil probe is best. A long piece of rebar will work just fine. If you are young and nimble a long bladed screwdriver will work but there is a lot of bending. We are going to probe for soft soil under the turf.

This is how we found the leak shown in the first picture. There was no indication of surface water and we could not find a soft spot except right where the water came out. The idea here is that even if water doesn’t show on the surface it is still there and has softened the soil around it. We started probing down into the soil using a solid push each time. If the probe only went in an inch or so we knew we were getting off track. If it went in further we knew we were ok. Moisture would also show on the probe. Sort of like the “hot and cold” game.

Once you’ve located the area expect a bit of digging to find the actual leak. The softest spot might not be right above the leak. The leak could be on the bottom of the pipe and traveling down the pipe way a bit before it starts perking up. It comes back to pressure and soil compaction.

If you have not found the leak at this point it would be best to get a professional involved.