So, my new machine arrives today...I'm excited! A Profitec Pro 700.

I plan on plumbing it in this weekend or next...so here are my questions.

I have a whole house water filter, a whole-house water softener and a whole-house Reverse Osmosis system. RO water is 10-15 TDS and tap is 350-400 TDS. (I don't know the other measurements, yet)

I have read and read and read and understand not to use the direct RO water. My question is "which water to use?"

Should I

1) Plumb in a calcite filter into the RO water and use that? That should be the "purest" but also add back in the necessary minerals for the fill sensor and flavor. or;
2) Use the filtered, softened water before the RO system? or;
3) Use the filtered water before the softener and RO system?

Thanks for any thoughts!

Well, the easiest and safest thing is to put a calcite cartridge before the machine, feeding that with the RO water. When I did, I used the largest one I could easily source, which was an Omni-Pure K5648 from here, and I mounted it vertically so that the water would go up through the bed for the most even contact. That worked pretty well, bringing up the TDS to the 50-60 range, which is enough to taste pretty good and not scale the machine. In fact I added a tap and used that for drinking water, since it tasted better than the straight RO.

You could also use a mixing valve, in theory, to blend 1/3 filtered incoming water and 2/3 RO to get you down to a reasonable level, and depending on what is in the incoming water that may or may not taste better (TDS doesn't answer the question, "parts per million of what, exactly?"). If you want to play with it, you could get some calcite from an aquarium store and create a saturated solution of it, and then brew some coffee with both trial mixtures and taste them.

Best,
David

Perfect...I got a calcite inline filter, and am plumbing it in today! Thanks so much for the reply. Will run the full test on the water afterwards.

Don't be surprised if you still need to mix in some standard filtered water. As your starting point is 10-15 ppm TDS, the calcite filter may only bring it up to a 30-40 ppm TDS range. Be sure to measure once you're set-up.