My water and sewer charges are calculated based o...

My water and sewer charges are calculated based on the square footage of the apartment as there is no individual meters..from last 2 months charges are getting increase +5 $ . i don't understand when they have increased the square foot size of my apartment..don't know how the water is measured using square foot of apartment. i want to pay for just the amount of water i used but not by square foot calculation..
1) so this means if 2 separate apartment of same size have 4 people and another have 1 person then for both apartment bill would be same.
2) If i go out of apartment for a month then still i would be charged same .. i don't understand i am charged for water or for the area of apartment....Totally not fair calculation.. 75$ for 975 square meter