Hi Vivienne
This is a tricky one but I would be guided by the recent Memorandum of 'who is responsible for what' issued by the LPI (formerly Lands department). Bear in mind, this isn't the law unless you have adopted it as a by-law, but it is a good indication of what the current thinking is on this.
2.17 Plumbing (includes bathroom, kitchen and laundry) – OC responsibility
i. Water leaking through tiles or from one lot and affecting another lot or common property.2.18 Plumbing (includes bathroom, kitchen and laundry) – Owners responsibility
j. Water leaking from a bath or shower and not affecting another lot.
k. Water leaking from shower, sink, laundry tub, bath or hand basin taps.
l. Water leaking through tiles and not affecting another lot.
m. Damage to a lot caused by any water leak mentioned above, as a result of the problem itself.
Note, it doesn't say where the tiles are, just where the effect of leaking tiles shows up.
Now, your by-laws may be different and this is not law, per se, but this memorandum is based on existing laws, expert opinion and case studies so it does carry some weight in the absence of any other clear definitions of who's responsible.
You can download the full Memorandum HERE