I just submitted two articles, one an article on RO filtration and and the other on DI Filtration (direct ion exchange). The moderators, or who ever, should have it reviewed and posted by tomorrow, I assume.
With small tanks I recommend that people just go to home depot and buy an under counter model and if they have really bad water just add a full sized filter housing with a full sized DI cartridge for around $45. The home RO will only be rated at 25 to 35 gallons per day, but with a small tank that is more than adequate, and it comes with full sized filters not the toy in-line ones that come with the cheaper ebay 6 stage $99 filters. Plus it will have a small holding tank that will give you RO water on tap for drinking, cooking and coffee making. Plus they furnish all the plumbing fittings, adapters and RO faucet. Thety do require some DIY ability though. Not much, but some, none the less.