Adding a DI chamber to an existing household RO unit?

[hillegom]

I would think you need a storage tank, one with the rubber bladder in it. It would give you the pressure you need plus, when you ask for drinking water upstairs, you will get a glass, not a trickle.
I installed a tank for my friend in his basement and it worked fine.
Not endorsing these guys, but here is a pic of the type of tank I mean.

http://watergeneral.com/product10.aspx