Who is liable to pay if leakage from the floor above creates problem

Dear Sir / Madam, I am a resident of housing society. My flat is on 2nd floor. There is leakage in my bathroom and bedroom from flat which is on 3rd floor. After checking the flat bathroom (3rd floor) by plumber, the cause was found to be leakage of water through the tiles. The owner of flat on third floor is asking me to share ( 50 %) the amount of repair. Society chairman says it is the sole responsibility of flat owner of 3rd floor, but still the owner is not trying to negotiate . I wanted to know is the flat owner on 3rd floor solely responsible for payment ? or should it be shared 50-50 by both of us ? what does the housing society rule recommend? Kindly waiting for your reply Thank you