Rain water is foul. It is full of atmospheric pollutants that you'll need to scrub out. Not to mention bird crap and leaf litter from the rooftops. Used to know Jamie at Bermuda Triangle brewery who RO'd his rain water before use. Pain in the butt according to him. But according to a leading beer website, that brewery was closed in 2002. Still, I recall other folks using rainwater with lots of hardware & precautions. I'm sure you can do it, but it's not a free ride.
If you're tapping out your well, is it possible to run it into tanks during off-peak usage for later use? We have four 2,000 liter tanks we use as a buffer for our (unreliable) municipal service. Gets us by a day or two when they have no water for us. Good luck!