While this seems like a simple question, it is actually rather complex. Different sprinkler heads emit different amounts of water and it is impossible to know exactly how much water your system puts out over a period of time without actually testing it. The manufacturer's specifications for the sprinkler heads will list a precipitation rate, but this is water pressure-dependent and you should still test your system. Testing can be done with something as simple as a soup cans or a milk cartons, or you may obtain irrigation catch cups for this purpose from your county USU Extension office. The testing is described in detail on the following website: http://www.uc.usbr.gov/progact/waterconsv/pub_select.html