well if you had a association for all the flats it would have been advisable to take association permission before installing private water tank . all decisions have to be taken by registered association . meeting ought to have been called wherein decision of water shortage placed on agenda . based on resolution passed in the meeting further decisions should have been taken .
what you have done is sidestepped the association . now request the association to regularise the installation of water tank considering acute water shortage in building . or association can install bigger water tank of say 10,000 liters to resolve water problems of all members of the association
