I’m hoping someone from Victoria will jump in on this because the law there is different from NSW in so many ways (yet exactly the same in others).
I guess the question is, did you do something to cause the water leak (inadvertently, obviously) such as retiling your bathroom but not having it waterproofed properly?
Or was it a fault with common property piping that happened to be serving your lot?
Simple answer – write to your committee and ask them to put in writing why they think you should pay for this and why they haven’t claimed it on building insurance. Their response may speak volumes.