There are preformed plastic flashing pans that you can use under the door or you can create one with thin sheets of lead or modern rubberized asphalt based flashing tape.
How to fix sliding door water leak.
Check the weatherstripping or flashing.
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.
Aim a garden water hose with a sprayer set on mist or low at the outside of the sliding door.
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.
There are countless videos online that show you how to install these flashings under a door or window.
How to stop water leaks under a door frame.
Cover the bottom of the side jamb with the tape.
Press it tightly against the jamb including the corner.
How to fix a sliding door leak.