I know someone who had a real high water bill one month, like hundreds of dollars over. They tried to get the city water department to not charge them since it was so strange but the city did not back down. They never were sure where that excess water went but it seems it only happened that one month. Someone must have left the hose running or something.
Cities are crappy that way. I know of more than one person who had a leak develop between the meter and their house, and they discovered it when they got a water bill for hundreds of dollars. Not only did they have to fork over a couple of grand for a plumber to come over with a backhoe to fix it, the city stuck with their demand for the water bill.