If you like the idea of rain water, you GOTTA run calmag in it, then adjust the pH.
Most city water is fine for soil grows, or even hydro grows if the nute system is forgiving (canna for example- in MA and the Northeast you can get it only at the Liquid Sun shops or online). I run Canna in both my soil and hydro grows, both on city water.
Rain water, remember it has Sulfuric and Nitric acid in it from atmospheric gases. Check the EC before you decide to run it. If it has an ionic strength that even registers on a cheap probe/meter, you might want to look elsewhere, since you don't know WHERE the EC is coming from. Unknowns=problematic.