bathroom subfloor replacement
I have had to replace a utility room floor and subfloor, a kitchen floor and subfloor and part of a bathroom floor and subfloor over the years due to water leak damage.
I ALWAYS go back with pressure-treated plywood (3/4" subfloor and 5/8" flooring). I may have to replace it once due to water damage, but I will never have to replace it again.
It costs a bit more for materials that way, but once it is done with the proper materials (and that means pressure-treated only anywhere there is potential water damage like the above rooms), then you're doing it for money well spent.
If you have any specific questions beyond that (how to, etc.), just ask and we will be glad to help you.