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How brewers read a water report

The six ions that matter, their useful ranges, converting alkalinity to bicarbonate and calculating residual alkalinity to see whether your water suits pale or dark beer.

23 Sept 2026 · 7 min read

Beer is over 90% water, so its minerals directly affect mash pH, yeast health, clarity and flavour. A utility or lab water report lists many parameters; brewers need to focus on six ions (1 ppm = 1 mg/L).

Ion	Brewing range	Role
Canxi · Calcium Ca²⁺	50–150 ppm	Quan trọng nhất: hạ pH mash, bảo vệ enzyme, giúp men lắng và bia trong · Lowers mash pH, protects enzymes, aids flocculation & clarity
Magie · Magnesium Mg²⁺	10–30 ppm	Vi chất cho men; nhiều quá gây vị đắng chát · Yeast nutrient; harsh above ~30
Natri · Sodium Na⁺	0–70 ppm	Ít thì làm tròn vị malt, nhiều thì mặn · Rounds malt at low levels, salty when high
Sulfate SO₄²⁻	50–350 ppm	Làm đắng hoa bia sắc và khô · Sharpens and dries hop bitterness
Chloride Cl⁻	20–200 ppm	Làm thân bia tròn, đầy · Fuller, rounder body
Bicarbonate HCO₃⁻	0–250 ppm	Hệ đệm chống giảm pH: cản bia sáng, cần cho bia tối · Buffer: hinders pale beers, helps dark ones

Common unit conversions

Total alkalinity (mg/L as CaCO₃) × 1.22 = bicarbonate HCO₃⁻ (ppm).
Calcium hardness (as CaCO₃) × 0.4 = Ca²⁺ ppm; magnesium hardness (as CaCO₃) × 0.243 = Mg²⁺ ppm.
If the report only gives “total hardness”, that's calcium + magnesium as CaCO₃ — you need them separately for accurate numbers.

Residual alkalinity — pale or dark beer water?

Residual alkalinity tells you how much the water still pushes mash pH up after calcium and magnesium are accounted for: RA ≈ alkalinity (mg/L as CaCO₃) − Ca²⁺/1.4 − Mg²⁺/1.7 (Ca, Mg in ppm). RA near zero or negative suits pilsners and pale lagers; 50–150 suits amber and brown ales; higher RA suits stouts and porters because roasted malt is strongly acidic.

Other things to check

Chlorine / chloramine in tap water: causes medicinal chlorophenol off-flavours. Remove with activated carbon or one Campden tablet per ~75 L.
Iron and manganese: keep below 0.1 ppm — more gives metallic flavours and haze.
Well water is often hard and alkaline: blend with RO water or start from RO and build the minerals.

Tap water in Ho Chi Minh City and many provinces changes with the season and the supplying plant. For brewpubs and commercial brewers, the reliable path is an RO base with minerals added per recipe — every batch comes out the same.