The water purifier includes a nozzle (9) in a jacket pipe (1). At least one inlet bore (21) connects an inlet-side section of the jacket pipe (1) to a turbulence chamber (19), which is open towards an outlet-side section of the jacket pipe (1). When flowing through the inlet bore (21), a water stream is deflected and is swirled in the turbulence chamber (19). The rotating water stream subsequently passes through the magnetic field of at least one magnet (11). This efficiently prevents deposits of limestone or scale.