Leakage from above flat kitchen sink in my bedroom

I stay on the first floor in a 13 floor housing society in mumbai. Water leakage from problem in the kitchen drainage in the above floor is coming into my bedroom. I have spent alot of money painting and fixing my walls still water is dripping from above. The owner of the above flat although leakage is completely within his kitchen house is asking me to pay 50 percent for repair of his kitchen leakage. Society is also asking me to pay 50 percent. I spent so much money repainting my bedroom walls which went waist due to above flat leakage and society want me to pay 50 percent to fix this ? Is this correct as per law? If not what is the correct law and how i can ensure the above flat owner fixes the leakage at his own cost ?