well if mineral reduction is your only concern, just run a commercial sized mixed bed DI. contact your local purified water dealers, and see about the costs of renting a tank. but there will be zero waste with this type of purificiation but the bottles wont last as long as if it was pretreated with reverse osmosis. RO is able to be more efficient by using a recycle system, where a portion of the concentrate water is recycled into the feed side of the ro and ran through again. for every gallon of water the machine i maintain makes, a half gallon goes down the drain, so very efficient as far as ro's go. but a system like that is far to expensive and large for a hobbiest. there are also technologies such as electrodeionization and ultrafiltration, but again very expensive.
