I think it is very important to have DI as well. It is very good for removing silicates and polishing the water after the RO stage is complete.
If you remove the DI component from the system and plug in a TDS to just the RO section you will get a pretty high PPM reading still. Attach the DI and watch it drop to nearly 0.
At home I have 2 TDS meters in my RO/DI so I can measure the water at each stage. Water comes in from 200 - 300ppm, is about 30 - 40 ppm after the RO stage and 0-6 ppm after the DI. (This is just from memory)
I am getting a MAKO system soon with 2 DI Units instead of the 1. I am expecting 0 ppm permanently from this.
I can give you actual readouts if needed.
Keith
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