A leaky toilet is one of the main causes of high water bills. You may have a leak and not hear it. Here's how to check:
Drop a dye tablet, food coloring or colored drink powder mix into the tank. Wait 1 - 2 hours without flushing the toilet) to see if the color travels to the bowl.
If you see color in the bowl, call a plumber to repair your toilet, and you'll see your water bill go down.