Alkalinity to bicarbonate converter
Water reports state total alkalinity in ppm as CaCO₃; brewing chemistry runs on bicarbonate. This converts one to the other exactly, splitting alkalinity into HCO₃⁻ and CO₃²⁻ at your water's pH.
How it works
Alkalinity is the water's acid-buffering capacity, titrated to pH 4.3 and expressed as CaCO₃ (50 ppm CaCO₃ = 1 meq/L). At any pH the carbonate system splits that capacity between bicarbonate and carbonate according to the second dissociation constant (pKa₂ = 10.33): the converter computes both species exactly. Below pH 9 the shortcut HCO₃ ≈ 1.22 × alkalinity is accurate to within a couple of ppm.
FAQ
Why does my water report list alkalinity as CaCO₃ instead of bicarbonate?
Labs measure alkalinity by titrating with acid to pH 4.3 and express the result as equivalent calcium carbonate — a convention, not an actual ion. Brewing calculators work with the bicarbonate ion itself, so the number needs converting.
What if I don’t know my water’s pH?
Use 8.0 — most municipal water falls between 7 and 8.5, and below pH 9 the answer barely moves: bicarbonate is simply about 1.22 × alkalinity, with carbonate near zero.
When does carbonate (CO₃²⁻) actually matter?
Only above roughly pH 9, where the carbonate share of alkalinity becomes measurable. For typical tap water it rounds to zero and you can ignore it.
Is “temporary hardness” the same thing?
Temporary hardness (also as CaCO₃) equals alkalinity in most potable waters, so if your report lists temporary hardness instead, you can usually use it here directly.
Method: textbook carbonate equilibrium (see A.J. deLange, “Understanding Alkalinity and Hardness”). The same function drives the brewwtr calculator's source-water tools.