A water pump for a spa or the like has a pump water inlet, a pump water outlet and an impeller driving water from said inlet to said outlet. The impeller provides the water axially introduced at the pump water inlet with a radial component which delivers the water to a large plenum chamber surrounding the impeller and which plenum chamber has an increasing cross sectional area as the water moves from the pump water inlet to a plenum chamber outlet thereby reducing backpressure in the water. The plenum chamber terminates with the plenum water outlet located closely to the impeller and a smooth transition area defines the area extending from the plenum chamber outlet to the pump water outlet. The water outlet preferably extends so that the water has a directional component which is generally parallel to the direction of the water entering the pump through the pump water inlet.