A good starter unit that in my opinion is excellent is this one
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I've been using it for a year, have changed the filters once and overall am very pleased with it. It is dirt cheap and portable so you can stow it away when not in use.
Just keepin mind that over the long term that unit above will work out to be more expensive than say this one
75 GPD RO/DI 5 Stage *PLUS* System - English
which is a lot more expensive. I am gonna buy the BRS one thats right above this week, I make alot of water and I think I'm familiar enough from using the smaller one to use the bigger one. LOL