It could be that the drainage holes are blocked,use a piece of thin wire in the hole and wriggle it a few times then use a straw and blow down the holes the water should come through onto the sill unfortunately if it is not rectified it will eventually fill up.if this doesn't solve it use a dry cloth to mop the water up.

Drain holes be blocked at bottom of door

Generally with leaks to doors there could be many issues like no drip bars to sash, no compression to door mechanics or even gasket failure.
Drainage can be a possible too and can be checked easily.
Last of all the fitting of the door itself whether square or not.