Diagnosing a leak is very simple, the only tool you need is a wrench to open up the lid to your meter. Here is all you need to do:
1) Find out where the sprinkler system begins. Sprinkler companies typically connect in one of two places: 1) in your basement right after your main water shut-off (generally in your furnace room) or 2) at your outside water meter.
2) Locate the valve boxes at your property. These are green boxes usually found in mulch beds or on the side of your property.
3) These are your pressurized water lines (we referred to these lines as the main lines). These are the only lines which will leak. The water for the other sprinkler lines stop at the valves. Now examine the area where you think you may have a leak, if the wet area is located between the main water connection (see item 1) and a valve box or between two valve boxes, you may have a leak. Otherwise, your wet area could be due to something else. Here are a list of things to consider:
a) You are overwatering this area, especially if you have spray heads located in the area. Spray heads emit a large volume of water, watering more than 10 minutes 2-3 times a week could be excessive.
b) It is a low lying area where the water builds up and doesn’t have anyplace to drain to. The Northern Virginia soil is red clay and holds water. The remedy could be one of two things: turn the sprinkler zones off in this area for a few days or look at hire a drainage company to assist you with this problem