...the solenoid-operated valve that creates the water drops.

(The black cord going off from the little white nozzle, below the clamp, to the right of the image is my
focussing aid! On the other end of the cord is a weight - a small nut, actually - and letting this dangle
down to the surface of the water in the tray below gives me something on which to focus the camera,
so the images of the transient water splashes are in focus!)