The other day I came across a fascinating modification of your standard electroluminescent displays, which have local activation in response to water. This video explains how they work.

Some additional demo videos can be found here:

https://www.youtube.com/watch?v=3qTol_4_k3o

https://old.reddit.com/r/interestingasfuck/comments/1f0oe15/...

https://old.reddit.com/r/water/comments/123j8sw/electrolumin...