Recently I figured out why our water bill went up by $10/month. I had thought originally that it was due to us having another roommate, but the last time that we had a new roommate it only went up by a couple of dollars. The new roommate we have now is only at our house 4 nights a week, so I didn't think it was him.
It came down to our downstairs toilet lever is sticking sometimes. I went down into our basement and heard running water, but knew no one was running the water. Went upstairs and the lever was stuck. This weekend I'll be replacing the lever and hopefully in a month or two we will see the benefits of it on the bill. Right now our bill is at $40/month for water & trash service, which is pretty good still for 5 adults taking showers and 4 adults using the washer (1 takes clothes up north on the weekends to his other home).