I would have to agree with those who say there is probably a leak somewhere TBH.

We are billed separately for water and sewer, but our bill is averaging $160 a month combined for 4 people. So 2-4 showers a day, dishwasher ran at least once a day, and 6 to 8 loads of laundry a week min..

On.. and my upstairs bathroom tub is broken. It isn't just a drip, it is now a full STREAM of water at all times, and unfortunately hot water. Getting it fixed in the next few weeks (80 yr old house with original plumbing.. so not a DYI project!!) but honestly, think like if you turn you water on with the facet so it is just running, purely on hot, 24/7 is how it is, and our bill is only about 25% more than yours! Before that leak it was about $100 a month combined, so those leaks do really really ad up!