All you need is a 100,000 gallon cistern and you could fill it from roof rain.
Absolutely!
My 50 gallon rain barrel has been filled an emptied 10x already this Spring! I save milk jugs, then put the water in there (a gallon at a time) and use it for both water and HEAT in the greenhouse as we go into Fall. I really only have 30 gallons in there, right now.
I’m at maximum capacity as it is! I’ll talk to Beau about a Cistern - I had one at my other farm.
Currently close to flood stage in Black Earth, WI. Our favorite shoe store, ‘The Shoe Box’ is located there and they WERE flooded out the last time we had this rainy of a Spring - which wasn’t all that long ago! (2019)