I started waterdrop photography about 4 years ago. First, all was manually done. To increase the recall factor, I built a device which can trigger valves, flashes and camera. In the end of 2010, I was a little bit bored by the standard waterdrop-pictures, I thought it would bring nice effects if I would use different colored waterdrops. So I decided to extend my setup up to 3 valves. It was not really easy to get the 3 drops from the different valves to the same path, but finally it worked.
This technique more or less became a standard, many photographers know it in between.