Alkalinity as CaCO3 and Bicarbonate

I am looking at the water report recieved, and using various spreadsheets to perform calculations (mainly because I am curious at this point). I am coming up with some variances in Alkalinity that don't seem to make sense. Here is what the water report has.

Bicarbonate 42
Calcium 26
Chloride 83
Magnesium 18
Sodium 170
Sulfate 310
Total Alkalinity as CaCO3 72
pH 9.2

From Palmer's book and Martin Brungard's Bru'n Water spreadsheet, it seems like Total Alkalinity as CaCO3 should be much lower, around 34.4 (42/61*50), expressed as a function of bicarbonate. Or Bicarbonate should be around 88.

Am I misunderstanding this relationship or is this a possible error?

That is some pretty darn alkaline water coming from your tap.

That is a pretty poor brewing water. The sodium is far too high and the sulfate may be problematic for some styles.

Yes using the Water Input sheet in Bru'n Water, its apparent that something is wrong with the reported information. Entering all the ions in the program and using the alkalinity conversion tool, it appears that the reported profile can be made to balance if the bicarbonate and carbonate reported from the conversion tool are used. For the 72 ppm Alkalinity and 9.2 pH, the bicarb is 76.5 and the carb is 5.6.

Brewers that want to learn about brewing water should download Bru'n Water. Click the link in my signature line to visit the site and download the program.

The alkalinity*61/50 formula does not work when the pH is above 8.3 as it is here. For your reported alkalinity and pH the bicarbonate content is actually 71 mg/L (assuming an alkalinity titration to the more or less standard 4.3 - if the analyst went to the equivalence end point bicarb would be 73). If you ignore ionic strength effects, of which you have beaucoup in your water because of the high mineral content) you would calculate about 75 (4.3 end point for alkalinity) and 77 (equivalence end point). None of these is remotely close to 42 so you must have misread or mis-typed the bicarbonate number because using the alkalinity by itself (you don't need the bicarbonate number if you have alkalinity and pH) gives a profile which balances quite nicely. It's really the alkalinity that is important because that's what determines mash pH. This water doesn't have all that much alkalinity but is obviously loaded with sodium sulfate. If it tastes OK I suppose one could brew with it but I wouldn't be adding any gypsum!

Thanks for the great info...Bru'n water has really helped me learn a lot. Good to hear the reported 42 bicarbonate looks weird to others as well. I was beginning to question my understanding (or my ability to enter numbers into a spreadsheet).

As far as brewing goes, I have to dilute the water prob a minimum of 50% for most, if not all styles, but after dilution I think it should work well for IPAs and the like. I am also utilizing ajdelange's great post on "water primer" to assist making the water adjustments within the Bru'n water spreadsheet. These two resources have been wonderful.

Thanks to all!