I agree that a holding tank is a good thing. If you're going to go to the trouble to have one of these units (which you should), then you may as well drink the water yourself.
When I bought my RO/DI unit I also got a nifty little meter that checks the disolved solids in the water so you can see when it's time for a filter change. The lower the number the better.
I checked my tap water and it was a whopping 62! The RO/DI water is 2.
I like the RO/DI water so much I plan on running lines to all of the sinks in my house so no matter where I go I have the "good stuff!"
The unit I got came with very clear instructions, the holding tank and a little drinking water spout that you attach to your sink.
I like it a lot! My dog sems to like the water too
My Uncle is a dentist, so I should mention this. If you only drink RO/DI water, make sure you use a toothpaste that has floride in it. Most municiple water systems fortify the water with flouride for healthy teeth. The RO/DI unit will filter this out. Your pearly whites will thank you!!