rain water is kind of like distilled, similarity is they both have 2 parts hydrogen and one part oxygen some molecular contaminants and some desolved solids in them.
when you distill water, you take out EVERYTHING for the most part is a desolved solid. When you Further RO the distilled water, you further take out all but the miniscule amount of non H2O molocules.
Rain water on is similar to distilled in that it evaporates from the ground, leaving most the desolved solids in the dirt, but once its re forming as droplets in the clouds, it re-aquires contaminants again, from wind born debris, and dirt dust ect picked up by mother nature, that mixes back with newly forming droplets of rain in the clouds. take rain water and distill it and be surprised at how much desovled solids are in the distiller afterwards. you my be surprised.
but unless you live in LA where Smog is just BAD, you wont find anything better than Rain water. and its true, Ph is not equal just because its rain water.
think about it, if rain water was bad, even by todays measurement of polutants, the earth would be brown, not green.
for what its worth,does MN run a PH test before she starts raining to water her world?