A bathwater circulating system has a pump operable to draw fluid in at an intake port and expel it under pressure at an output port. Water- and air-supply conduits feed water and air to the intake port at a rate determined by a flow-restricting air-intake valve so that the pump mixes the water and the air, pressurizes the mixture and thereby dissolves the air in the water, and expels the air/water mixture at the output port. A pressure-reducing valve is connected by an output conduit that extends from the output port to the pressure relief valve and conducts the water/air-bubble mixture from the pump to the pressure-reducing valve without separation of the air from the water and such that the mixture is at least partially depressurized at the pressure-reducing valve such that the air forms microbubbles in the water.

An inflatable spa is disclosed having improved strength. A water cavity of the inflatable spa may receive massaging air bubbles and/or jetted water.