I've been testing with crass on a bed of cotton, and the Netduino reacts quit fast to water being added, so I'm not so worried about that. I'm just thinking of submersing the pump in a bowl of water and connect it to a flexible tube.
MOSFET is news to me, but then again there's much electronics that would be. Is it the same as a small relay or something like that? Where can I get one (in Scandinavia )?