Use tap / city municipal water works fine ... I never let it evaporate or cast spells over it.
You water your grass outside ... Right ?
You water the bushes and plants outside too ...
R/O water is processed to remove certain minerals and other non essential elements.
BUT ... It strips off calcium and Magnesium ...so now you got to put that shit back in ...
Thus you are adding back CalMag or Epsom to balance it out ...
Don't make sense to me .... And i'm high right now
Chlorine is also an essential element for plants anyways.
Just check your local water for PPM baseline to make your feed mixes.
Adjust the PH to where you want it. And BOOM ... Magic Happens .