Firstly a caveat, I’ve not tested a bottle of water that actually matches the label some are close, some are miles off so although these calculations are pretty accurate the end results may not be as expected. You can easily test Hardness, Alkalinity, pH and TDS at home, most other figures need more advanced test equipment.
What are the key figures on bottled water when it comes to brewing coffee?
The units of mg/L and ppm are interchangeable.
Bicarbonates mg/L (or ppm)
TDS or Dry residue mg/L
What am I aiming for?
Total Hardness = 68-100 mg/L as CaCO3
Alkalinity = roughly half total hardness, can be slightly higher for espresso
TDS = 125 – 175mg/L
pH = 7
How do I get there?
You’ll notice that some of the figures on the bottle aren’t the same as those we are aiming for, luckily they are easy to calculate.
Calculating Total Hardness
Total Hardness as CaCO3 = (Ca x 2.5) + (Mg x 4.2)
Alkalinity = Bicarbonates * 0.82
So a worked example for Clearview would be
Label gives us
Ca = 15mg/L
Bicarbonates = 45mg/L
TDS = 100
pH = 6.3
Total Hardness = (15 x 2.5) + (5 x 4.2) = 58.5 mg/L as CaCO3
Alkalinity = 45 x 0.82 = 36.9 mg/L as CaCO3
Comments on Clearview – Slightly lower than ideal Hardness, ratio of 1.6:1 Hardness to Alkalinity which is also lower than ideal. pH of 6.3 is slightly more acidic than desirable and the TDS of 100 is also lower than desirable. All of these factors could add up to produce a clean cup with low body and something slightly bland or dull but that’s for another post.
Hopefully this gives you some useful tools to read and understand water bottle labels, there will be more posts on water in the future including how to make your own recipe from scratch.