What size nozzles are you running are they worn out, 2505 or 2504 or both. What speeds do you have everything on like Rinse speed 0,1,2 all those play a factor in how much water you use.
Go to the Water meter at the road at night at your carwssh when no one is washing there car and make sure no water is on anywhere mechanical room ect, and wash your car. Pay attention to the meter for gallons of water this probably would be the simplest option just has to be dead at your Carwash when you do this. Might even close it off at the road for 20mins wouldn't hurt. I am sure someone else on here could tell you another option also.