Pretty simple really. I had a squirt gun, a vase of water almost full with water, colored rocks in the bottom of the vase, lighting. Pulled squirt gun trigger slowly till it started dripping, tryed to time the drip hitting the water with the shutter: lots of trials, alot of intense timing. Used the camera flash, manual focus.
I would like to try this with an object hitting the water, and in a bigger space.