Overhead water tank

Hii... mehjabin here..my question is..in my building secretary is having overhead water tank including inside of home out side he has kept two extra the large one ..I am the chairperson of bmy society when I ask this so he says I am not using extra water then it's leaving time for everyone I am filling at that time...but the other flats don't get water in force... please let me know is the extra water tank aloud for the single flat