In February the master bath toilet supply line in my unoccupied house
failed. By the time the next-door neighbor noticed water coming out of
the house, all rooms but the front two bedrooms were flooded, and the
drywall was damp as high as 8" in some places.

This line was installed by the builder in 1998, and has a plastic
coupler at the toilet end. This coupler is what failed - it split open.
The result was approximately $25K in damage - most of the carpeting,
vinyl floors in both bathrooms and laundry, all of the MDF baseboards,
and repainting of rooms except the previously-mentioned front bedrooms.

State Farm took great care of us, and between the work done by a local
company to remove ruined stuff, dry everything out and do some of the
repairs, plus the work I did myself, we were able to move back into the
house starting in May.

But here's the thing: I inspected the coupling on the hall bathroom
toilet, and it was starting to crack too. So when I replaced them, I
tried to find supply lines that had metal couplings, but no joy.
They're ALL plastic now. But I noticed the new ones are made with more
solid thicker plastic than the ones that failed.

So my advice is this: Check those toilet supply lines, and replace them
if they look like they're starting to crack - it'll save you a lot of grief!

--Steve