No way is that correct! A DI filter performs the final polish.. it would not be a RO/DI unit without it. DI resin alone could filter your water straight from your tap to 0PPM, but would exhaust the DI very quickly. The RO membrane is used to reduce the work for the DI, and is mandatory in pretty much every DI situation. Buy a good membrane thats rejecting 98%+, that way you are maximizing your DI resins life!
I have DI with a 100gph membrane. It works just fine. If your changing your membrane to a different GPH remember you have to change your flow restrictor.
Do not use DI if you have a 100 GPD Dow Filmtec NF or nano filter membrane. It IS NOT a Reverse Osmosis or RO membrane rated at 96-98% rejection rate and NSF/ANSI rated for drinking water but is a 90% rejection rate NF filter designed and rated by ANSI/NSF for "Pool and Spa Use". Huge difference and it will go through DI resin many times faster than a Dow Filmtec 75 GPD RO membrane which IS 96-98% rejection rate.
Any legitimate RO vendor will try their best to talk you out of the Dow 100. The reason is, for every 2% you decrease the rejection rate you cut your DI life in half, imagine what going from 90% to 96-98% or higher will do for your DI life and treated water quality. A huge cost savings.
There are exceptions, I am speaking of the Dow Filmtec brand 100 GPD specifically, it was not intended for drinking water and does not provide 3 log virus removal as required by the EPA.
Another 100 GPD is the GE water membrane which is really similar to the Dow Filmtec 75 GPD in all respects except they test it at 65 psi rather than 50 psi like Dow. It produces 75 GPD at 50 psi, 90 GPD at 60 psi and 100 GPD at 65 psi all at 96-98% rejection rate just like the Dow 75.
Alex is speaking about a membrane wound by an independent winder using genuine Dow membrane fabric which is sold on the open market. Dow materials have one form of ANSI/NSF approval meaning it is suitable for contact with human foodstuffs but not necessarily approved as a wate rtreatment device. This can be confusing,
My only reservation is it does not have the ANSI/NSF treatment device approval yet which is a very expensive and time consuming process but I understand they are going through this process which is commendable. Myself personally, I prefer to use systems and materials which have been through this process as it ensures a level of quality standards not seen in most knock offs and imported ebay type systems. Hopefully Aqua FX will receive this on their own membranes soon as it will be a huge selling point. Until they receive the approval I cannot personally recommend them myself though but its great to have them on the forum helping out!
If you have time on your hands you can research the different ANSI/NSF standards, it is good reading and helps you understand why many of these standards are in place and why they are important to the end user.
I agree with the importance of the ANSI/NSF, and that is part of the reason we took on the task. We are very excited to finish up the process. We are nearing what we believe to be the end, so we have our fingers crossed that will have a announcement soon! Its great to know once we do, that we will have your approval! We truly strive to have top quality products and customer service and this will be a good milestone for that. We are also very glad to be a part of the forums, the more people can understand about what they are doing the less problems they will have (We hope!).