This question comes up somewhat frequently, and you will hear answers on both sides. But the issue at hand is only made possible by the oddity that for some arbitrary and unknown reason we have chosen to measure mineral levels in ppm rather than in milliequivalents.
Another derivation of the OP's question which is amazingly rare (and yet will shine light upon it as presented by the OP above) is: If I mash a recipe in 4.5 gallons of distilled or RO mash water and you mash the precisely same recipe in 9 gallons of distilled or RO mash water (such as for the case where I sparge and you prefer to no-sparge), isn't it a bit odd that (since we are both reading the recipe from the exact same book, and we are both making the same volume of finished beer, and this book is telling both of us exactly how many ppm's of minerals must be added) for some reason (as addressed by me in my replying paragraph above), although we are both mashing the exact same grist, in the exact same quantities, you seem to be adding fully twice as much mineralization to your mash as I am adding? I.E., if chemical reactions occur on the basis of weight to weight and valence to valence, and we are both adding the same weight amount of a reactant called "grist", shouldn't we both likewise be adding the same amount of minerals if we both expect the same degree and types of chemical reactions to occur, such that we are truly both making the same beer? Such can not occur if both of us are following instructions to add a certain ppm quantities of minerals, but it does occur for the case whereby we are both adding the same mEq's of minerals.
Or what if you mash in 5 gallons of distilled, and I mash in 6 gallons, whereby you sparge with 4 gallons and I sparge with 3 gallons. Same mineral issues apply. And only milliequivalent additions of minerals can keep us on the same track to make the same beer.
At this present juncture we find ourselves mired in a situation whereby myriads of time and myriads of books and training attempts (in one form or format or another) exist supporting the adding of minerals to the mash via ppm's and virtually zero of the same supporting cast exist in support of milliequivalents (mEq's). But fortunately for us, just as for climate science, science itself (as well as particularly the advancement of science) is not and must never be done via polling for a consensus. The number of supporters weighing in on the existing ppm side make zero difference in and bring zero relevance to the discovery of truth.
The above as I have outlined it exposes the nakedness of any validity one can attempt to bring to brewing in the name of "water profiles" such as are built upon ppm's.
