When tiling any areas that may be subject to repeated exposure to water make sure to use a waterproofing product to waterproof the area prior to tiling. Some types of ceramic tiles are porous and stone tiles such as travertine, marble, and granite are very porous. Water can seep through tile and grout and leak in to cracks at corners and other intersections.
The best way to protect these areas is to apply a waterproof product such as RedGard, NobleSeal, CompuSeal or any other such product for proper protection of these areas. A little bit of protection goes a long way in such moisture prone areas.