The idea I got was to regulate the water led in from the river to the cistern/tank underneath the building by building a form of sluice.
It is perhaps one of the simplest Minecraft red-stone builds possible, a lever leading to a sticky piston pushing and pulling a block in and out of the water channel from underneath.
If you are completely new to redstone and want to see the details of how to connect the lever and the piston, watch the video I recorded. I try to make things entertaining by sharing some of my life story and I also show more details of the Acacian Ascendancy, Flower Valley and surrounding area. Feel free to leave any questions here or on the video, especially if you are completely new to Minecraft, there might be things you are not familiar with which I take for granted.
Here are screenshots of the water channel outside the Ascendancy with the sluice open and closed
As I mention in the video I thought about moving the circuitry indoors to the cavern.
Since there is no filling water mechanics in vanilla Minecraft (yet), there is no automated sensor, but it would make sense to have the lever there for anyone spotting the tank being overfilled.
The next Minecraft-related update will be a tutorial for how to build a small overgrown jungle-home!