1. See here:
http://www.fehd.gov.hk/tc_chi/comments/joint_offices.html
2. You still need the government's assistance. Only the Government can force the owner for an inspection to determine the leak.
Without such determination, you don't have a strong proof for a lawsuit.
(If your suspicion is correct and the owner refuses to repair, you can repair in your own costs and sue for the amount against that owner._