Though grout can be repaired and you can re-caulk joints, if the shower pan is leaking, you'll need to have it repaired by a tile installer or roofing contractor.

Contact your homeowner's insurance company; repairing the damage may be covered. To check the shower pan for leaks:

1) Remove the shower drain screen.

2) Plug the drain with an expandable plug, purchased at a hardware store or home improvement center.