Really I think the cheapest way to buy it, is to take your own 5 gallon containers into the supermarkets that sell it that way. I have bought it from Kroger in the past, 30 gallons at a time. I loaded a shopping cart with my containers, filled them up, and rolled to the checkout. Told them it was 30 gallons and they rang me up. I thought it was about .30 a gallon that way. It was not ro/di, but it is ro water and they use UV on it. The tds is about 5-10, but that beats tap water hands down, if you can not afford or do not want to buy a ro/di unit.