Here’s how to build a Water Drop kit using a Raspberry Pi as a controller for a solenoid valve and camera trigger.
(Standard disclaimer applies, batteries are a fire hazard, wiring them up incorrectly can cause a fire, burning, etc., not to mention possible damage to equipment. Do so at your own risk, etc).
First, you’ll need to get yourself a solenoid valve. There’s loads of these on ebay for about €15.
We only need two GPIO pins, one for driving the solenoid valve, and the other for triggering the shutter of the camera. I used pins 17 and 18.
Since the solenoid is 12V, used a battery pack that takes 8 AA batteries, giving me about 11 volts, which works fine, and it’s more portable than needing an AC power supply.