Harold - I think you're missing something here. This is nothing like a swimming pool wall. Unlike the pool wall - which must contain the water - shower tile doesn't serve that purpose. That's why you have liners and membranes and the like under the tile. Grout does not stop water.
Slows it down, but doesn't stop it. It does keep the crud from getting under the tile, and cracks can let it through.
Like was said earlier, you need to verify the integrity of what's under that tile.