[GoatOfAplomb]

I think it's a really cool idea. How To Invent Everything (by Ryan North) describes a water logic gate that works as either AND or XOR gate depending on which drain you look at.

I have my doubts about pulling it off as he describes, though. It depends on two streams of water flowing out of angled pipes such that such that when they both flow, they collide and combine into one stream falling straight down. That seems pretty finicky to get right.

Edit: Someone did it! The AND gate worked great, the XOR not so much. So they made it out of greedy siphons instead: https://www.youtube.com/watch?v=IxXaizglscw

[usrusr]

Nice, can we call those solid state? I was thinking more along the lines of sluice gates mechanically operated by floats.