When a building only has one master meter and no submeters, it will be impossible to bill residents for actual usage. This presents a big problem. When there is not a direct correlation between what a resident pays and what a resident uses, there tends to be an increase in consumption.
Think of it this way If you go to an all you can eat buffet, you tend to load your plate up with as much food as possible, even if you aren't going to eat it all. This way, you get the most bang for your buck. The same thing happens when residents don't pay for their actual consumption. Showers and sinks seem to be left running longer and lights and TV's tend to stay on when no one is using them.