Just use all zeroes. It's not exact - RO filters typically leave some ions behind - but it's close enough.

 

Brewfather has the following for RO water, so ya, basically zeros.

 

Yeah that's about what I have, it's next to impossible to be absolutely certain so just selecting zeros is a viable alternative.

 

What you wind up with depends on where you start. I see from my TDS meter that ions are reduced about 90% - I measure tap water at 135 ppm and RO water at 12. It varies: In Winter, I get 6 ppm from my RO filter. I suppose I could have my water tested but when the sum of all of them is 12 (and there are 6 to begin with), I get more variance measuring the salts than from the water itself.

 

Just be sure of what you're buying, most stores here have at least two different waters. Distilled and Spring. The distilled will be your RO or all zeroes.
The spring water tend to be a municipal source filtered but not zeros. FYI

 

Looks about the same as Bru'n Water.

 

I've gotten RO out of the same dispensing machine that varied from <10 ppm up to ~30 ppm TDS. so there's really no set standard. Been using the default mineral content for RO found on Bru'n Water, which comes out to ~30 ppm TDS with good results.

 

An RO filter removes about 90% of all ions so there is always something left. In my water supply, I run between 6 and 13 ppm total dissolved solids so I can essentially treat it as zero. In reality there are some ions there but the amount is less than I can measure with the equipment I have (a scale that measures in 10ths of a gram), so I treat them as absent. There's not enough of anything to make a significant difference in any water profile except maybe Pilsen.

 

Yup. For what we're doing there isn't much we can do to get that level of accuracy.