The easiest way to determine if there is an active leak in the irrigation system is to use the water meter as a gauge. Water meters are equipped with a microdial that measures minute amounts of water flowing through the meter. This microdial is often shaped like a triangle or a star. If no water in the home is running (no leaking toilets, etc.) the microdial should be stationary. However, if the microdial is moving and no water is running in the house, you can shut the water off at the backflow preventer valve and recheck the microdial. If the movement of the microdial ceases, then we can assume that there is an active leak in the irrigation and you should have it serviced. If there is still movement of the microdial after cutting the water supply at the backflow preventer valve then there is a leak elsewhere in the waterline, but not involving the irrigation system.