Usually what is called defect periods around 7 or so years, depending on the state where you reside. In the Northern Territory, it is six years for structural defects and one year for non-structural defects. This possibly will be classed as non-structural unless the house has moved as a result of its construction causing water to leak.
It is also worth noting that most waterproofing used in showers is usually only guaranteed for 10 years, but should last longer. It is possible that the waterproofing has stopped functioning or something else is leaking (such as blocked pipe causing water to back up into the bathrooms causing the damage).
If it is from say a burst braided/flexible pipe, then these also have a life of about 10-15 years as well.
Unfortunately, if it isn’t claimable under your insurance policy, there might not be much you can do other than arrange the repairs yourself. I do wish I had better news.
One thing when you commission someone to fix the damage, it is important to find out the source of the water and ensure that this is also repaired. Otherwise, you will strike the same problem in due course.
Edit: Have you checked your insurance policy to see what is covered in relation to leaks and water damage (hopefully you have cover under your landlords insurance)? The first step may be to get someone independent to see the cause of the leak to determine if it is covered and also to work out how to move forward.
If you provide the name of the insurer and the cover you have, we might be able to assist.
The other option is was the leak and damaged caused by the negligence of the tenants (e.g. they put something over the drain hole causing water to flow into the house from the bathroom). This might e another avenue to explore as they might be responsible.
Have you inspected the property to see the damage and what may have caused it…or are you relying on others to provide this to you? I would be inspecting the property to see what may have caused the damage and its extent as well.
