Home Improvement Questions? Ask a Handyman for Answers
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If there was a puddle on the floor there's a pretty good chance that wasn't the only water that escaped the shower. If you see signs of water downstairs when there's no water on the floor then that's the time to complain to the builder. It's extremely unlikely that the water seeped through the tile. It's much more likely is found it's way through a crack where the wall or shower meets the floor. This is a caulking issue which is a normal maintenance item not a warranty issue unless you have a tiled base(board).
Unless there is a noticeable flaw in the grout there's really no way water can seep through the tile/grout, thinset, tile backer & plywood before it can get to the ceiling below. If this problem re-appears regularly then mention it to the builder.