these days i BUY distilled water straight from the grocery store because i cant trust city water any more. 

Alot of people like to talk real proud about their well-water or using rain water and the actual quality DEPENDS and where you live and the chemicals in the air and what is in the ground. many MANY variables. if you were in Michigan, for example it might not be ideal 

to get back to your initial question, RO is good but you need to use much more calmag because it contains no actual minerals