Toiles are areas which ar always in contact of water.
Mostly the surface finish in toiles are ceramic tiles with tight or spacer joints installed in cement paste on scratch coat plastered surface of wall.
If water leaks through joints of tiles in dado or from dado and flooring joint. The leaked water forms a damp patches in room behind that wall.
Repairing those leakages are expensive because new tiles wont match in color and texture of what you had before, no guarantee of same type of tile available in future.
To avoid the leakages on walls, the base coat of conventional type waterproofing is taken on wall around 1 feet above the finish floor level.
In case of chemical or any other type waterproofing, you need to do the same...