This type of hydro massage works only with air, you can have plates of various sizes and shapes or as in this case punctiform, under each nozzle incorporated in the concrete there is a frame of rigid PVC pipes that draws the shape and connects the various exit points. air, these can be positioned on stairs, benches or swimming pool floors, are controlled by a piezo-electric button that activates an air compressor.
The effect is that of a gurgling of water over a large pool surface and the massage you receive is soft but at the same time intense.