Not that I have done this yet; but you can take the cue from water harvesting. Currently, I fill all my clients water features and pools with Rachio, but I calculate the loss according to Et /inches and replace automatically with check valves and emitters or not.
I would try the following though for water reservoir you have. 1. 24 VAC 115 AC Relay. 20 Amp SPDT with Nema Housing 2. Little Giant has a Piggy Back Vertical Mechanical Float Switch. you have a high and low setting. 3. If your landscape usage is more than your rainfall, you can add a potable supply to top it off below your high mark with an autofill and float. I like to calculate the landscape usage, and reservoir and calculate the durations for fill, depletion and usage. When I have a couple extra bucks and time to do it, I’ll try it but you’ll see the advantages to the piggyback switch as the pump is always wet. Pumps are expensive and I’ve replaced several in large ponds difficult to get to basins, and wiring , many if not all with a faulty float switches.
I may have missed a part since , I looked this up days ago… however with system and the 24 VAC relay you can then select any zone on the controller and program it any way you want, especially having the back up potable line you’ll always have the adequate water volume for your plant requirement. Good luck , up date your progress! Thank you.