- it really depends on how bad your water was to start with and how good your RO
membrane is. RO
membranes will take out anywhere between 95 and 99% of the impurities. Normally DI
resin will strip the rest of it away so that you have truly pure water. Personally... I'd go with the DI
since you're going to the trouble of doing RO
water to start with - why settle for "almost" pure water. It might be worth investing in a cheap TDS
meter to measure the TDS
(total dissolved solids) of your RO
output water. If it's truly pure, it should read zero. If it doesn't, then you'll have to make the decision of how much it's worth to you to get that last bit out.
You can add a DI
stage as a separate add on, inline with the output of your RO
system. Fairly inexpensive and no need to change anything with your existing RO
system. Check out thefilterguys.biz - you can get stuff cheaper, but these guys are top notch.