I enjoyed Gordon's commment in the book where he says, 'don't mess with the water too much'. Since creating RO or DI water is 'messing with' water to the extreme, I'd say that what Gordon needs to revise that statement to is: 'don't add too many salts to water'. In my discussions with Gordon, that is what he really cautions against since he and I have tasted too many beers at competition that have a minerally soda water flavor that doesn't go away. There are too many water calculators in the brewing world that don't really provide good guidance for mineral and acid additions. Even Palmer's sheet has some outrageous upper limits for some ions that end up letting the brewer 'hang themselves' with too much mineral content in the water. I've tried to make it apparent to brewers using Bru'n Water where the limits are and why they shouldn't go there.
That's fair. Spreadsheets are models, and not all models are accurate. Some only work within certain ranges. Most will get you into trouble if you trust them blindly.
My comments were in response to seeing how perfectly reasonable data could be misunderstood and misapplied, and result in beer that didn't taste right. So I was giving a hard caution to the contrary.
Personally, I like the taste of beers with light mineral additions. Taste is subjective, though. But when I stop tasting the beer and start tasting the water, I know there is something wrong.
Martin, was your tool new when you announced it here? I don't remember hearing about it before.