The shower scene takes from both Psycho 1960 and the intro scene in Halloween 1978 where Michael Myers kills his older sister.
There are certain places in your home that should be a private and safe environment, the shower being one of them.
Killer Tomatoes Strike Back 1991 As decades passed, the Psycho shower scene had been done to death another intended pun.
The Burning 1981 : Done for a cheap jump scare and gratuitous nudity.
The shower scene at the start of this film has the bones of the Psycho template, but none of the meat.
At least Jason did the dirty work himself.