A higher than normal water bill could be an indication of a leak. Leaks can waste hundreds of gallons of water down the drain and can cost you hundreds of dollars as the leaking water registers through your meter. A dripping faucet can use up to 15 gallons a day; a 1/16" opening can use 943 gallons a day; a 1/4" opening can consume 60,900 gallons a day.
The most common and costly types of leaks can be toilet leaks. The tank should be checked to make sure that there is not a continous overflow leak or a leak due to improper seating. If the toilet is operating properly, you may want to check faucets for worn washers or defective fixtures, check outside water taps to be sure they are completely turned off, check your water heater overflow pipe, check the humidifier tank that has a float arm and overflow, or for an underground leak. It may be necessary to call a plumber to help identify and/or fix the leak.