Here is a link for a deionized tank, these are filled with cation/anion mixed bed resin. A prefilter and carbon end filter would be all thats needed to produce really high quality water.
[Ebay Link Removed] Park International Fiberglass Water System Tank Tanks RT1447 | eBay[/url]
This is the resin you would fill the tank with. You can get a lot of water through through this set up before exhausting your resin ( dependent on initial water quality )
New Siemens - NR-6 at Watersurplus.com