[chrismorse]

Most likely, it is the toilet(s). I just had a water billl go from $60 to $175. I found a flapper held open by a link in the pull chain. This can be an intermittant "leak". Get rid of any excess chain length.

I've had the city, (water company) forgive a huge water bill for a leak i doccumented and fixed for a client - worth checking. They may do that only once a year or not at all. Still worth asking once you've got it fixed.

I cannot count the old worn out flapper valves i've replaced. It needs to be clean and supple. As above, get rid of any escess chain that might foul the closure of the valve. To improve the water flow, try the "Corky" flapper valve with a yellow foam float on the chain. This float prevents premature closure and allows more water into the bowl.

If the toilet water valve isn't shutting off completely, the water level will rise to the top of the "stand pipe" in the tank, then overflow down into the bowl. This may or may not make enough noise to hear, but it is worth checking. If close to the top, adjust the float down a bit, then recheck.

If you have a big place, check all of your out buildings/faucets. Seen it happen.

If you shut off the valve where the water enters your house, but the meter is still turning, then the leak is between the meter and that valve - fixed a few of those

Lastly, if your toilets and hose bibs are all ok, you need to check the hot and cold water supply pipes, (where accessible). I've fixed pin hole leaks in copper pipes under the house and in the attic, as well as rusted through galvanized iron pipes and broken plastic pipes.

Good luck,
chris