I was thinking, since Sparkfun stocks small DC motors and Servos, then stocking a simple DC water pump would also be great. It wouldn’t be too hard to control with a microcontroller ( just use a npn to turn it on, and a diode to handle inductive loads). I bet a lot of people can work on some new liquid based projects with the addition of this item.
I think too it should be a good idea to add a low power DC water pump as Sparkfun products.
A Bi-stable electromagnetic micro-valve could be useful for water based projects.
Both must be easy to connect to a MCU
I would love a Dc water pump. I could make a robot that sinks and floats by pumping water in and out!
Perhaps you could consider something like the 12v DC pumps used in various liquid-cooled computer solutions. I have used them before and they are very reliable, I ran the pump almost continuously for eight months before reselling it on eBay.
SFE could sell a Miniature Latching Solenoid Valve.