It depends. If the water damage occurs in a common area, the HOA is usually responsible for it. If the water damage occurs in a separate interest, the owner of the separate interest is usually responsible for it. In some cases, the HOA may be responsible for water damage in a separate interest if it resulted from the association's negligence or if it started from a common area the HOA covers. This can be a tricky situation, though, so it is best to tackle such issues on a case-by-case basis.