If its a shower bathroom, I would relocate that door or put in a shower screen with a shower tray..

If it is an external door then put up a roof and a front porch to minimize water damage to the door..

Standard building designs don't allow standing water anywhere near a door frame..

If it's just the bottom part can't you send the door to a carpenter to remove the timber plywood laminate and replace it with a plastic or water proof laminate?

If you can DIY then it might be easier to just cut the damaged part and replace it..

That's if you don't mind the look..