This .01M filter for H2-Series water ionizers can be used on untreated water. It's therefore perfect for well-water. It has eight stages of protection highlighted by CaSO3 to reduce heavy metals and different forms of chlorine, .01micron UF hollow fiber technology and two stages of the highest quality carbon. You only need one of these, to go on the left side of your H2 Series ionizer. It's rated for 500 gallons.