An appliance body which includes a fluid delivery system providing a fluid flow to the appliance body and an exit for the fluid. A cavitation assembly is responsive to the fluid flow, and includes a constriction or obstruction member, wherein the flow rate to and through the cavitation assembly and the flow velocity and other factors results in a cavitation number in the range of 0.1 to 6, so that hydrodynamic cavitation is produced at the exit of the appliance for delivery to a treatment surface.
