Water problem

We are residents of a co-op housing society since 1995 And since 2011 we are facing water shortage problem reasons : 1.Because we stay on 3rd floor 2.water we used to get was very less After requesting committee people again and again they agreed to give us seperate water line to solve the water shortage problem. Earlier they were just ignoring us and after giving a strong letter they agreed. Recently a new tenant has purchased the flat on second floor and staying there since june 2017 . And they were given a watwr connection from the same seperate line that was given to us and now we are facing drastic water shortage problem due to that. At the time sharing of line was happening we told them that this is going to happen but committee people didnt agree to us and they did whatever they wanted to. We are going to give them a letter asking for a seperate pipeline to sort out the water problem if not we will take a legal action on the same So now my question is Is there any legal action that we can take on committee people . Is that okay to mention . Or tell me if there is any other appropriate way to tighten their knots