Compulsory strata building insurance doesn’t cover lot contents.
So to have any chance of claiming from either the OC/BC or its insurer, you’d have to establish the OC/BC’s liability which usually means establishing their negligence.
With water leaks, especially from storms or burst pipes, it can be sometimes difficult to establish that negligence. If the OC/BC failed to maintain gutters properly they might be negligent. If it was a building failure eg due to a storm or a 100 year rain event they might not be negligent.
It’s usually easier to claim on your own contents insurance and leave any consequential claim against the OC/BC to them.