We lived in a rental property where there was a flat below the house we rented, which was rented separately by a single guy. We were on the same water, and the landlord somehow split it so we each paid something.
He basically took the water bill and divided it by the number of people living in the whole property (four), then charged us each for the number of people we had in our separate flats (three in ours, one in the guy's). But we were paying a FORTUNE in water -- like, hundreds of dollars a MONTH. It turned out the guy downstairs, who was a carpet layer, was washing his huge work van twice a week using the outside hose. Still makes my blood boil thinking about all that water he wasted that we ended up paying for.
I would ask the landlord if separate meters can be installed for the water usage as this has the potential to turn very bad for you, the tenants who are spending the most time on the premises but not necessarily using the most water.