If you can lift cover over the water meter and observe the dial on the water meter you can perform the following tests yourself. If you have a problem observing the water meter dial ask for a usage audit. Call the water department.
Start here: »www.hernandocounty.us/utils/
If they do not serve your home they can tell you who does from your address.
I normally use around 20,000 each month which includes lawn irrigation. One month my bill showed a usage of 41,000 gallons so I called the city water department for a FREE usage audit. The procedure the water department technician used was simple. He turned off all water in the home and irrigation system then observed the meter dial. If the meter dial indicator continues moving then you have a leak somewhere.
Most homes have a valve to shut off all water flow to the irrigation system and a separate valve to shut off water flow to the home plumbing system. First turn off the valve to the irrigation system. I had a high water usage in my previous residence one month and it turned out to be a leaking solenoid valve in the irrigation system. If the meter continues to show flow after turning off the valve to the irrigation system the problem is a leak in the homes plumbing. If the dial stops moving after shutting off the valve to the homes plumbing while the valve is open to the irrigation system the problem is in the irrigation system. If the meter shows water flow after turning off both valves the leak is between the meter and the shut off valves. By the way many homes have a T fitting at the output of the water meter with one line going to the irrigation system manifold and the other line going to the home plumbing. That is to reduce pressure drop in the home when the irrigation system is running.
Whether or not a leak is found the next step is to turn on each irrigation zone one at a time using a watch with a second hand and observe the water meter dial to determine how many gallons of water each irrigation system zone consumes per minute. If one zone's usage is substantially higher than the others there probably is a break in an irrigation system line. I had a broken line. When I ran the zone where the break was for a short time and I observed higher usage than the other zones and discovered a puddle form where the break was located. You can multiply the number of gallons used per minute by the number of minutes each zone is set to run for, by the number of days the irrigation system runs each month, to calculate the number of gallons lawn irrigation consumes each month.