I should also mention in my research of RO/DI systems that I read somewhere, (anyone correct me if I'm wrong) but you should make sure that your filters go from larger micron size to smaller micron size and not small to large and in addition, no micron size larger than 5 micron. Mine is set up to go 5 micron sediment, to 5 micron carbon, 1 micron carbon before it goes into the RO membrane.
Senji also told me to check to see if my water company uses chloramine instead of chlorine to purify the water because many municipalities are using the chloramine now, instead of chlorines. If so, the carbon filters will need to be the type that will remove chlorimines as regular carbon filters will only remove chlorine.