Tile and grout are not waterproof. Water gets through them every single day, and what happens next depends entirely on what's underneath. A shower built without a real waterproofing system will fail; the only question is whether it takes two years or ten.
A properly built shower has a continuous waterproof membrane behind the tile on every wall and under the floor, lapped so water always runs down and out to the drain, never into a seam. The floor is sloped toward the drain before the membrane goes in, so water never pools in a corner.
Before any tile goes up, the pan should be flood-tested: plugged, filled, and left for at least a day to confirm nothing leaks. It costs a day of schedule, and it's the single best insurance you can buy for a bathroom. If a contractor skips it, ask why.
When you're comparing bids, ask three questions: what waterproofing system is being used, how the floor slope is built, and whether the pan will be flood-tested. Clear answers to all three tell you more about the finished shower than any tile sample will. Every Silva Bathroom & Flooring Corp shower gets all three, and we're happy to show you the pan before we tile it.