Believe it or not, water falls to the floor when you shower
I could hold a long lecture on the merits of waterproofing, but I won't, as I'm a bit short for time atm. I'll say this though:
The floor and about 1 metre up on the walls, in a 1 metre radious from the shower fitting, are the most important surfaces to waterproof properly, as those are the areas which aree going to be exposed the most to water. Pay particular attention to a proper seal around the drain. I assume the floors are concrete, but know that concrete isn't (normally) a waterproof material. Damp concrete can weaken, and be attacked by mold. Damp can also infiltrate more sensitive areas through concrete. Need to go. Back later.