I have a before/after TDS monitor on my RODI system. I have only ever seen 1 or 2 tds (mostly 1) after the RO membrane, and always 0 after the DI filter. My incoming tap water is around 40 - 70. I also have 2 pressure tanks (3.2 g each) after the RO membrane (and before the DI), so that provides some buffering of flow from the membrane. And I have an RO only feed to a faucet on my kitchen sink, so I don't waste DI resin when filling water bottles or whatever.
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