RO or RO/DI water will always be better than using any other source, treated or not. If you can use it, do it. I used to use the RO water from machines at the grocery store but I installed my own RO/DI before upgrading to my current tank. It's been a life saver. Also seriously consider how much you'll save in gas that you won't have to drive out to the store to pick up more water, etc.