If your toilet is not the culprit, other leaks are not so easy to see and can also cause your water bill to be high. If you have a high water bill and the toilet seems to be operating properly:

1. Check all faucets. Replace worn washers or defective fixtures.
2. Check outside water taps to be sure they are turned off at the faucet.
3. Check your water heater overflow pipe.
4. Check a humidifier tank that has a miniature float arm and an overflow.
5. Check for an underground leak.

If these steps do not solve your problem, you may need to call a plumber.