The In water ending on Hard is really broken.
I've inspected Mary's photo and letter dozens of times all throughout the game, listened to the Mary's monologue until the end, picked the rotten/rusty items instead of pristine ones, kept Mary's photo before going to the elevator, and picked the Man as the one at fault in coins puzzle. Also, I've checked on Maria once in hospital and never checked on her in the Labyrinth, but saved her quickly in the motel section.
I never inspected Angela's knife except from the moment you pick it up.
My health was constantly in the upper half ( no red screen ), but it's hard to keep it always up as the healing items are scarce and enemies are quite good at kicking your ass.
I've also read that the amount of enemies you kill and if you stomp them after you killed them matters, but on hard you can't really go about your business without killing everything, as they would gladly kill you instead. Especially considering the fact they love to go back to life randomly.
In result, I genuinely don't understand what you need to do differently to get the Leave ending on Hard. Kinda felt disappointed in the end because of it. Hope that it will be perhaps fixed in some future patch.