I am the secretary of an OC. As I understand it, the OC is responsible for waterproofing UNLESS it is damaged in any way by a resident/owner, who is then liable for its repair. In this case, I would want clarity on exactly where the leak is coming from, before doing anything else. Is it certain that the leak that is evident in the kitchen is coming from the ensuite above? If yes, then where in the ensuite is the leak coming from? If it is the area where there was a grouting repair 4.5 years ago, is there evidence that that grouting repair damaged the waterproofing? If yes, then the owner of the townhouse is liable for the repair of the waterproofing since that owner would have been responsible for the repair of the grouting. A waterproofing expert should be able to answer these questions.