a housing;

a water reservoir adapted to be mounted on said housing for supplying water to said humidifier;

a source of ultraviolet radiation having at least one outer surface;

an enclosed helical sterilizing path in said housing through which water from the water reservoir flows, the enclosed path formed by a portion of the at least one outer surface of the source of ultraviolet radiation and an open faced helical conduit which is placed against the outer surface of the source of ultraviolet radiation such that the outer surface substantially seals the open face of the helical conduit to create the enclosed helical sterilizing path, such that water flowing through the sterilizing path flows around the source of ultraviolet radiation and is bounded by the portion of the at least one outer surface of the source of ultraviolet radiation and is exposed to ultraviolet radiation at least once to reduce a level of microorganisms therein;

a moisture dispersal unit on said housing connected to said path and receiving water therefrom for dispersing moisture into air traversing said housing, all water being dispersed by said moisture dispersal unit having flowed through the sterilizing path and having been exposed to ultraviolet radiation therein prior to dispersal; and

a pump in said housing connected to said sterilizing path for circulating water therethrough so that at least some water supplied to said moisture dispersal unit is exposed more than once to the ultraviolet radiation along said sterilization path.