Sliding doors come in a variety of types. Some are "pocket doors" which are interior sliding doors that are concealed in a wall pocket when open. Other sliding doors are made of aluminum and glass and are usually designed for entry in and out of a home. Most often, these glass sliding doors are on the rear of the home and lead to a back yard or pool. Occasionally, these sliding doors leak and need to be repaired.
Test the door for the location of the leak. Aim a garden water hose with a sprayer set on mist or low at the outside of the sliding door. Spray the door, and look for the leak location. If you cannot re-create the leak problem, inspect the interior of the door for stains or rust.
Check the weatherstripping or flashing. Weatherstripping and flashing are rubber insulators located on the bottom of the sliding door that secure the gap between the threshold and bottom of the door. Replace damaged weatherstripping or flashing by removing the old and attaching new weatherstripping with screws or adhesive.
Check the doorjamb and the frame surrounding the door. Inspect the doorjamb and door frame for worn or damaged caulk. If worn or damaged, scrape away with a putty knife. Wipe the area with a rag and apply new caulk with a caulking gun.
Check the glass seal. In some cases, the seal between the door frame and the glass will decay. Apply a clear coat door and window sealer or caulking.