Will I Have To Share Cost Of Repair Work If The Flat Above Me Is Leaking.

I live on the ground floor of a four-storey building in Mumbai. The bathroom of the flat above me has bad plumbing and over the years the water has leaked into my flat removing plaster and paint. I complained to the society and the owner of the flat and I were called for a meeting. The owner agreed to repair the plumbing in his flat but said that I would have to pay 50% of whatever cost will be incurred. My question is, do I have to do that. The source of the leakage is solely from the flat above and all the harmful effects are on my flat. I have agreed to pay for all the repair of plaster and paint on my end but why should I pay for bad plumbing in the flat above. Isn't that his responsibility? So my question is do I have to pay in a share or can I legally refuse to do so. Thank you!