In a waveguide pump and method of pumping liquid, at least a portion of an elongate ultrasonic waveguide is immersed in a liquid reservoir. The waveguide has first and second ends, a nodal region located longitudinally therebetween, and an internal passage extending longitudinally within the waveguide from the first end to a location beyond the nodal region toward the second end of the waveguide. The waveguide also has an inlet at the first end in fluid communication with the internal passage and an outlet in fluid communication with the internal passage and spaced longitudinally from the inlet beyond the nodal region of the waveguide. The immersed portion of the waveguide extends from the inlet to a location that is one of generally longitudinally adjacent, at and beyond the nodal region of the waveguide. The waveguide is ultrasonically excited to cause the waveguide to vibrate at an ultrasonic frequency.