DI is for final water polishing via Ion exchange..it's like squeezing the last drop out of a sponge. The bulk of the filtering process is done through the RO membrane. Here are some stats from Spectra Pure website
www.spectrapure.com:
RO unit:
remove over 98% of all ionic impurities
remove over 95% of organic impurities
remove colloidal and particulate impurities
remove microorganisms and pyrogens
remove chlorine, chloramines, pesticides etc.
RODI unit:
remove over 99.9% of all ionic impurities
remove over 95% of organic impurities
remove colloidal and particulate impurities
remove microorganisms and pyrogens
remove chlorine, chloramines, pesticides etc.
In my opinion, why bother with the DI filtering if you're going to skip out on the reverse osmosis step that takes out 98% of the ionic impurites? DI is a marketing gimick IMO..it's to sell the dang unit..in most applications it's not needed.