As the process of reverse osmosis removes MOST minerals and debris from water, it doesn't remove ALL of them. The Distilling process as well as Ion Exchange would create the best and most purest form of water available today, and also make the best resource for any application. On the other hand RO-filtered water would definitely be better than tap or mineral/spring water as they are both loaded with contaminants, calcium, and other minerals from the earth. The minerals, mainly calcium, is what would be responsible for clogging up your atomizer over time.