Potential Causes of High Water/Sewer Bills An unusually high water bill is most often caused by a leak or change in water use. Some common causes of high water bills include: 

-A leaking toilet, or a toilet that continues to run after being flushed (see additional information below)

- A dripping faucet; a faucet drip can waste 20 gallons of water a day or more 

Additional Info.