The most common cause of leaking shower doors is a breakdown in the caulking around them. Caulk should be firmly in place around all shower doors, and if it is poorly placed, or becomes damaged, it no longer forms a waterproof barrier between the shower doors and the bathroom floor. In order to prevent shower doors from leaking, it is a good idea to recaulk the entire area.
Caulking Shower Doors
It is a common mistake of homeowners, when they come across shower doors that are not properly sealed, to add a layer of caulking directly over the top of the failed caulk. In fact, more layers on top of the old area will usually increase the problem or at least make it significantly worse. Before recaulking, remove the old material from around the shower doors.
Ensure that any drainage holes around the doors are not blocked by the old caulk, and then, using a 100% silicon-based caulk, cover the outside of the shower doors' frame. Add new caulkikng over the inside of the shower doors as needed, taking care not to cover drainage holes, and making sure that the caulk seals properly against the doors. Leave to dry before testing the shower doors to make sure that they are now waterproofed.