If they are built properly in the first place and well maintained, you may never have to deal with this problem in either of these rooms, but if you have moved into an older home that already has damage to it, you may want to try and invest the money to have the support structures re-done.

Weak floors are a sign of rotting or termites, so if you can bounce up and down on your toes and the whole room shakes or if objects lean toward the center of the room, you may have weak floor joists. These need to be replaced as soon as you can.

Look for missing areas of grout, caulking, or cracked areas of flooring. If you do end up having to replace the floor in the bathroom, you might as well try to renovate the whole thing, if you can.

As long as you are replacing the floor, you may want to consider installing a waterproofing membrane such as a product from Schluter called Ditra. This creates an extra seal between your bathroom's subfloor and the tile or whatever flooring that you choose to install.

Water damage also occurs to the ceiling just as much as it does to the floor, but most people do not usually think about it. When you renovate your bathroom or are having a new one constructed, you should always have an exhaust vent installed. If you do not have one, you may recognize them either from other homes you have been in or hotel rooms.

These are definitely a worth while investment, since steam absorbed by the drywall can cause it to crack and collapse over time. The first sign that you are having a problem is the mesh tape used to hide the drywall seams coming loose from the wall. It will start to become visible, since it is losing its adhesive properties.

Most people have rugs in their bathroom to help soak up some of the water that gets inevitably dripped on the floor and this is a good thing. Try not to let water stand on your bathroom or kitchen floor for long.