 What's going on with each sprinkler head? Because a lot of times the lawn mowing people will knock a head off. You're not aware of it or just jar it. Even just jarring a head with a wheel of a lawnmower is enough to make a leak. It won't be obvious when you look at the head, but the sprinkler comes on and there's a geyser right there. So that's one thing to look at. You can also look for leaks in the pipes themselves, pipes underground feeding pipes.