Masters of Suspense
The bath has been a source of inspiration for many film-makers, not least the "masters of suspense" themselves, Alfred Hitchcock and Henri-Georges Clouzot.
In both Psycho and Les diaboliques, the murderer is in fact two people, a couple engaged in an illicit affair in Clouzot's case, and the schizophrenic killer's split personalities in Hitchcock's. Something else these two films had in common was the insistence of both directors that no-one be permitted to enter the auditorium once the film had started.
Finally, Hitchcock's enthusiasm for Les diaboliques prompted him to ask Boileau-Narcejac to write him a screenplay... the result was Vertigo.