Definately get the RO
unit. the DI
portion is really important too. There are units you can get on ebay that work great (that's where mine is from), or you can go to a vendor like airwaterice.com and get one.
Since you're in an apartment, you'll probably want to get one that runs from your sink faucet. It's just an attachment you'll need to get - rather than tapping into your plumbing.
The main thing you want to look at is to make sure you're getting a 0 TDS
system. As long as the unit can generate 0 TDS
water, you'll be good to go.