Sounds to me like maybe there is a leak in the irrigation system. Possibly an irrigation main line leak if you're going through that much water.
So here's how we diagnose that.
First, make sure all water in the house is totally off. If there is an isolation valve that turns off water just to the house, turn that off. If not, just make sure all toilets, water faucets, dishwashers, washing machines, and icemakers are all off.
Next, verify that the sprinkler system is currently off. Don't turn off water pressure. Just make sure that the system isn't currently sending out water through the heads. Keep the water pressure to the irrigation system on.
Now go to your water meter and see if the small very sensitive dial on the water meter is moving at all. Typically, the most sensitive gauge on a water meter is this little triangle. See a few examples here;
or
See the little red triangle? You're looking for something like that. If it's moving at all, you have a leak.
Now we need to figure out where the leak is. If you have an isolation valve for the irrigation system, turn that off now.
Go back to the water meter and check that little triangle again. Did it stop moving? If so, then you have a leak in the irrigation mainline OR a valve is leaking. That's the only two possibilities.
Now let's back up. Suppose you check this first and the little triangle isn't moving. Suppose it's just still. So the next thing I'd want to eliminate is that there isn't a break in the house plumbing somewhere. So turn back on the house water pressure. Does that make the triangle turn now? If not, that's good. No leaks in the house.
The final thing to check for is a leak in one of the lateral irrigation lines. That's a lot harder to detect and diagnose.
So the way you have to do this is to go through each zone of your irrigation system. Start with a zone where you think perhaps there could be a leak. Maybe one with big tree roots nearby? Or one near where a fence was recently installed? Or just pick any zone. If the zone has spray heads, you can just turn the screw down on the nozzle that's on top of each of the spray heads. If you turn that screw far enough it stops all water flow. The head will pop up but no water comes out. Now turn on that zone so all the heads are popping up. Be sure no water is coming out of the heads. Check water meter again.
If the heads are not spray heads, and are rotors instead, then it's even more work. You have to manually remove each rotor and install a screw on cap where the rotor was. Once that's done, pressurize that zone and check water meter again. You do this zone-by-zone until you find the one that's leaking.
It's a lot of work if there is a break in a lateral line. Might just want to hire a good irrigation tech. if you find that there isn't a leak in the irrigation mainline or home plumbing. Because going zone by zone doing this with the laterals is a Pain In The Butt!
Good luck.