There are pre formed plastic flashing pans that you can use under the door or you can create one with thin sheets of lead or the modern rubberized asphalt based flashing tape.
How to fix sliding door water leak.
Weatherstripping and flashing are rubber insulators located on the.
Aim a garden water hose with a sprayer set on mist or low at the outside of the sliding door.
Check the weatherstripping or flashing.
Http youtu be hg2mfndacfw waterproofing how to weather seal door threshold water leak.
Place the end of a strip of adhesive backed aluminum tape on one of the side jambs in the doorway 3 inches above the threshold.
How to fix a sliding door leak.
There are countless videos online that show you how to install these flashings under a door or window.
Cover the bottom of the side jamb with the tape.
Test the door for the location of the leak.
If you have a water leak at your threshold you must watch this how.