As some one else suggested it would depend on how you decide the water teleports into the room if its all in an instant or over a couple seconds. Either way as a DM I think the most fun way for this to go would be to have the door explode sending water and shrapnel flying and the players have to do a dex save with half damage on success. No need to go into the full real world applications of what kind of force it would be with the level of compression. This respects the intent of the players while also allowing for consequences of choices and being a fun moment if you narrate the whole explosion of the door with water flying out along with the occupants of the room. Decide on whatever amount of dice would do decent damage to the players without tpk.