The invention relates to a liquid purification assembly using ultraviolet light irradiation against reproduction of pathogenic microorganisms, comprising an irradiation chamber (200) having an internal volume and comprising an inlet (204) and an outlet (205), the irradiation chamber (200) being provided with ultraviolet light emitting means (208) configured to irradiate liquid in the irradiation chamber (200) with ultraviolet light. The irradiation chamber (200) comprises a mechanism configured to cause a change in the internal volume of the irradiation chamber (200), said change in internal volume drawing liquid into the irradiation chamber (200) when the volume of the irradiation chamber (200) increases, and forcing liquid out of the irradiation chamber (200) when the volume of the irradiation chamber (200) decreases. The invention also relates to a beverage dispenser and to a method for purifying a liquid.
