A bath is a room or fixture used for washing, which exists in both the Muggle and wizarding worlds. While most wizarding homes like The Burrow and Number Twelve, Grimmauld Place have functional, ordinary bathrooms, the most notable and opulent bath described in the series is the Prefects' Bathroom at Hogwarts. Located on the fifth floor of the castle, behind a door with the password of the week (such as “Pine-fresh”), the Prefects' Bathroom is a place of luxury. The room is vast and constructed from gleaming white marble. Its centerpiece is a large, rectangular swimming-pool-sized bathtub sunk into the floor. The tub is filled by a complex array of approximately one hundred golden taps, each with a differently coloured jewel set into its handle. These taps release not only hot and cold water but also a variety of pre-mixed, magically-enhanced bubble baths, such as one that fills the entire tub with thick, purple bubbles. The room also features a white linen curtain, a chandelier of candles that illuminates the space, a diving board at one end of the tub, and a large painting on the wall depicting a beautiful, sleeping mermaid on a rock. This mermaid is known to interact with the bath's occupants.
The primary role of a bath in the series centers on the Prefects' Bathroom, which is the setting for two pivotal events. In Harry Potter and the Goblet of Fire, Harry Potter uses the bathroom to solve the mystery of the Golden Egg, a clue for the Second Task of the Triwizard Tournament. Acting on a tip from Cedric Diggory, Harry takes the egg into the bath. With help from Moaning Myrtle, he discovers that he must open the egg underwater to hear the Merpeople's song, which reveals the nature of the task. This moment is crucial for Harry's progress in the tournament. In Harry Potter and the Half-Blood Prince, the Prefects' Bathroom becomes the site of a violent confrontation. Harry, using his Marauder's Map, follows Draco Malfoy to the bathroom, where he finds Malfoy crying and confiding his fears in Moaning Myrtle. When Malfoy spots Harry, they begin a duel. The duel culminates with Harry casting an unknown spell from his copy of `Advanced Potion-Making`—Sectumsempra—which inflicts deep, bleeding gashes on Malfoy's chest and face. Professor Snape arrives just in time to perform a counter-curse and save Malfoy's life, a scene that deepens the animosity between Harry and Snape and highlights the dark turn in Harry and Draco's rivalry.