When there is water leak in the property, it is a headache for most people. Even more so when it is inter-floor water leakage. Both units (upper and lower) will need to work together to try and resolve the problem.
For HDB (Public Housing)
Public housing (HDB) usually operates on the basis of “shared responsibility”, i.e. split cost. The HDB will arrange for staff to visit and evaluate the likely cause of the leak and assist to coordinate repairs for upper and lower floor unit owners.
Here are three contractors listed on HDB website
For Private Non-Landed (Apartments and Condominiums)
In the case of private properties, under the law, it is presumed responsibility of the upper floor unit, unless proven otherwise. If you are living in a private property and experiencing leaking problem, check out this article about identifying and potential solutions to water leaks.
Covered under Building Maintenance and Strata Management Act, and Upper Floor is presumed liable unless able to prove to the contrary.