Beer's source water and Bicarb/Alkalinity, a speculative ballpark "What if?" question:

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Larry Sayre, Developer of 'Mash Made Easy'
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What if it is nominally "presumed" (as in speculatively presumed) that a ballpark typical naturally derived source water has within it a ballpark 150 ppm (mg/L) of Alkalinity (as CaCO3), and also thereby, a ballpark 180 ppm of Bicarbonate ion?

And what if one starts from this nominal ballpark baseline and then acidifies said water to ~5.40 pH for use as sparge water, for which the remaining Alkalinity will factually be on the order of ~15 ppm, and the remaining Bicarbonate will factually be on the order of ~18 ppm? Nigh on all of us would (incorrectly) presume at this juncture that the water we are sparging with is quite effectively both Alkalinity and Bicarbonate free.

And additionally if one starts with this same source of water and then adjusts their mash to pH 5.40, the mash itself is taking place within an environment whereby the remaining Alkalinity will nominally be on the order of ~15 ppm, and the remaining Bicarbonate will be on the order of ~18 ppm. Yet the beer will generally be fine to very good if overall process parameters are all kept to within norms as to practical standards. And yet again nigh on all of us would once again presume at this juncture (I.E., at mash pH 5.40) that the beer we are creating is both Alkalinity and Bicarbonate free.

And then what if along comes an endlessly repeated proclamation (or Mantra) that assuredly better beer can be made via the use of Deionized, Distilled, or amazingly good RO water as the foundation, wherein its Alkalinity is on the order of Zero to 2 ppm, and its Bicarbonate is on the order of Zero to perhaps 2.5 ppm?

Might it not be better to add ballpark 1 gram of Baking Soda to each 10 gallons of the likes of Deionized, Distilled, or amazingly good RO water whereby to place it on a level HCO3- and Alkalinity ballpark playing field with that of acid adjusted (to pH 5.40, be it for sparge or within the mash) natural source water?

What if beer loses some of its defining character if denied the active presence of some minimal level of HCO3- (Bicarbonate, the prime source for Alkalinity) ions?

Short version: What if no (or insufficient) residual HCO3- makes Johnny a dull beer?

PS: I'm fully aware that by the time fermentation is over both Bicarbonate and Alkalinity (as CaCO3) are likely to have finally achieved an actual ppm level of right near Zero, but what if the dullness/damage occurs upstream of the terminus of fermentation?
 
What if ...

To move beyond "what if", consider offering an "experiment" for people to try:
  1. Provide a (tightly focused) update to either the brewing water chemistry FAQ (here) or it's "cliff notes" page.
  2. Provide a recipe that demonstrated (to you) that the changes add value
  3. Allow time for people to try it (perhaps multiple times)
 
Low or no alkalinity water may be good for brewing some styles, but it can be less than desirable for brewing styles that have acidic grains or additives (porters and stouts are examples). All brewing requires acid, but some grists bring too much acid to the table and that means that having a proper dose of a buffer in the water can be important.
 
From what I can gather most British styled beers require very little water hardness 15 to 50ppm as CaCO3
 
A couple of additional notes:

For those who offer published approaches to water adjustments that use just CaS04 & CaCl, they note that they get good results for the recipes / styles that they talk about. Everyone tastes beer differently.

In other sections of the forum, people have noted that 300ppm in some brown ale recipes results in beer that is minerally for them (but not for the person who wrote the recipe). Everyone tastes beer differently.

As for what happens when people endlessly proclaim that (for them) "water chemistry is a rabbit hole", others are willing to offer advice on getting started with water adjustments. No need for spreadsheets, just measuring spoons or a highly accurate jewelry scale.

Brewing water chemistry FAQ (here) or it's "cliff notes" page are roughly 10 years old.

Precision jewelry scales are easy to buy and easy to use.

An update to either would convert academic brewing science into pragmatic brewing - and move everyone forward.
 
Since when acidified to pH 5.40 the carbonate species extant in water are ~10% HCO3-, if one begins with 200 ppm HCO3- (Bicarbonate) water, and acidifies it to pH 5.40, there will be nominally ~20 ppm of HCO3- (Bicarbonate) remaining within the water when at pH 5.40.

And if one begins with 300 ppm HCO3- (Bicarbonate) water, and acidifies it to pH 5.40, there will be nominally ~30 ppm of HCO3- (Bicarbonate) remaining within the water when at pH 5.40.

Etc..., Etc...

So if one begins with ~3 ppm Bicarbonate water (such as for Distilled) and acidifies it to pH 5.4, there will be only ~0.3 ppm of HCO3- (Bicarbonate) remaining within the water when at pH 5.40.

Some peer reviewed commercial brewing literature from yore indicates that water with up to 50 ppm Bicarb seems to be fine (as is) for sparging, and water as such will lead to no negative effect. But the same sources stress that one should best reduce Bicarb to 25 ppm just to be completely on the safe side while sparging with it. So if your water is starting out at greater than 250 ppm Bicarb you will need to acidify it to below pH 5.40 if you intend to sparge with it.
 
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