A liquid treatment system has a housing defining an interior space. The housing has an inlet port for receiving liquid into the interior space of the housing and an outlet port for allowing liquid to exit the interior space of the housing. The outlet port is spaced from the inlet port so that liquid flows through the interior space of the housing from the inlet port to the outlet port. An ultrasonic waveguide assembly is disposed within the interior space of the housing and includes an ultrasonic horn disposed at least in part intermediate the inlet port and the outlet port of the housing. The ultrasonic horn is operable at an ultrasonic frequency to ultrasonically energize liquid flowing within the housing. An ultraviolet light source emits ultraviolet light into the interior space of the housing to treat liquid flowing therein.
