Sliding door is not water proof, the only thing that connect the sliding door and railing is the wheels, and usually only have 2 set of wheels, the rest are just empty space.

If you want to prevent water coming in from the bottom sliding door meaning the bottom part need to be air tight, and that is not possible.

I seen people putting wood to prevent water going into the house from the door / sliding door. What they do is securing the wood with plasticine and this is very manual work.