Dang that is a good idea.. I just Trust my float valve lol in the future I am going to install some optical sensors from the apex so it will tell me when the bin is low or full..I've seen a couple of water change stations that incorporate a really good idea that you might want to try as well. With the top water container...and bottom one as well...you can't see how much water is actually in the containers without getting on a latter and looking into the container.
So, I've seen where people will drill and put a uniseal on the side of the container at the bottom and at the top. The run a small pvc pipe out with a 90 degree elbow (bottom one pointing up, top one pointing down), then between the 90 degree elbows put a clear piece of acrylic tubing! As the water fills the bucket, it will also fill the acrylic tube and you can always see how much water is in the bucket! I've kept this in the back of my mind as something to do for my water station whenever I get off my lazy hind-end and make it happen!