Handling water may possibly become my first Arduino or RaspPi project, if I can get through my newbie ignorance, and learn some new tricks as an old dog.
We have flood irrigation that comes in from an acequia every couple weeks (used to be every week, but times are changing) at an irregular rate at irregular time-of-day. (You can't deal with this, just using timers, and the amount of water pressure is tiny compared to what you usually have on a typical garden hose, so lots of cheap ubiquitous gadgets don't work here.) I leave a floodgate open (i.e. remove a coffee can from the end of a tube), go to work, go back home for lunch, go back to work, go home at end of day. For various reasons that you can probably imagine, it's bad to leave the floodgate open after we have collected a certain amount of water. Things work out fine if it happens to finish at lunch time (or if it's so slow that it hasn't finished until end of day), but otherwise, someone has to leave their workplace and go home to deal with it.
That is lame, in a way that really does (slightly) matter.
Thus I'm tempted to either build a sensor (or just cheeze out with a webcam, though that's less geeky) and some kind of remote-controllable motorized floodgate.
AFAICT nobody sells anything for this; it's up to me. As it happens, there are lots of guides online for building this kind of stuff, but they're all within the context of Dwarf Fortress! Yeah, right, as if I want a gate that'll remain stuck open just because there's a butterfly or elephant carcass in the way.
Lower tech solution: find retired neighbor to do it, in exchange for beer or something. This is actually the cheapest/smartest way to do, but rubs me the wrong way. I'm sure you all understand.