Home Brewing Water Chemistry Calculator

Enter your source water report, the percentage you are cutting with reverse osmosis or distilled water, and the salt additions in grams for the full batch volume.

Take a 30-litre batch built on moderately soft tap water (22 ppm calcium, 6 magnesium, 14 sodium, 28 sulfate, 20 chloride, 65 bicarbonate), cut 50% with RO, then treated with 8 g gypsum and 2 g calcium chloride.

The dilution halves every source ion first: calcium falls to 11, sulfate to 14, chloride to 10, bicarbonate to 32.5. Then the salts add 80.3 ppm calcium, 148.8 ppm sulfate and 32.2 ppm chloride across 30 litres.

The finished profile is 91.3 calcium, 3.0 magnesium, 7.0 sodium, 162.8 sulfate, 42.2 chloride, 32.5 bicarbonate. The sulfate-to-chloride ratio is 3.86 to 1, firmly hop-forward, dry and accentuated, which is exactly the West Coast character. Calcium at 91 ppm sits comfortably inside the 50 to 150 range brewers target, and sulfate at 163 is assertive without approaching the 350 ppm point where it starts tasting harsh and mineral.

Residual alkalinity comes out at 0.1, which the calculator labels moderate: suits amber and lightly roasted grists. Many brewers aim lower for a very pale West Coast grist, and the formula note below explains why this figure reads higher than some other brewing water tools would show.

Dilution: each source ion × (1 − RO percentage ÷ 100). A 50% RO cut halves every ion.

Salt additions: ppm added = grams of salt ÷ batch litres × the ion contribution per gram per litre. Each contribution is the ion's share of the salt's formula weight × 1,000, calculated from standard atomic weights: for gypsum, CaSO₄·2H₂O at 172.17 g/mol, calcium is 40.078 ÷ 172.17 of the mass, or 232.8 mg per gram. Recomputing every salt from the IUPAC standard atomic weights reproduces the table to within 0.1 ppm.

Per gram per US gallon (the per-litre figure ÷ 3.785): gypsum 61.5 ppm Ca and 147.4 ppm SO₄; calcium chloride (dihydrate) 72.0 ppm Ca and 127.4 ppm Cl; Epsom salt 26.0 ppm Mg and 102.9 ppm SO₄; baking soda 72.3 ppm Na and 191.9 ppm HCO₃; table salt 103.9 ppm Na and 160.2 ppm Cl; chalk 105.8 ppm Ca and 322.1 ppm HCO₃. Enter a 3.785-litre batch with 1 g of gypsum and the calculator returns the same 61.5 and 147.4.

Final ion = diluted source ion + every salt's contribution.

Sulfate-to-chloride ratio = final SO₄ ÷ final Cl. The calculator labels below 0.5 malt-forward, 0.5 to 0.8 leaning malty, 0.8 to 1.5 balanced, 1.5 to 3 leaning bitter and above 3 hop-forward. These bands are a widely used homebrewing rule of thumb, not a published standard.

Alkalinity as CaCO₃ = HCO₃ ppm × 50 ÷ 61.016.

Residual alkalinity, as this calculator computes it = alkalinity as CaCO₃ − calcium ppm ÷ 3.5 − magnesium ppm ÷ 7. The divisors 3.5 and 7 come from Paul Kolbach's brewing-water work in the early 1950s, where they apply to milliequivalents per litre; that is the form Brew Your Own gives in its article on residual alkalinity and pH. Applied to ppm of the ions, as here, they subtract less than Kolbach intended. With everything expressed as CaCO₃ the terms become roughly calcium ÷ 1.4 and magnesium ÷ 1.7, which gives about −40 for the West Coast IPA water rather than 0.1, about −57 for the hazy water rather than −23.0, and about 72 for the stout water rather than 91.0. Until the tool changes, treat its residual alkalinity as a direction rather than a precise value, and expect it to read higher than tools that use the converted form.

Building from 100% RO water is the cleanest approach because there is nothing to subtract: you are constructing the profile rather than correcting one.

For a 23-litre hazy IPA, 1.5 g gypsum and 5.5 g calcium chloride produce 80.4 calcium, 36.4 sulfate, 115.3 chloride and a sulfate-to-chloride ratio of 0.32: malt-forward, soft and rounded, which is the mouthfeel a hazy is built around. Residual alkalinity is −23.0, appropriately low for a pale grist, and calcium sits in range at 80 ppm.

The identical batch size for a stout takes a different shape: 2 g gypsum, 2 g calcium chloride and 4 g baking soda give 43.9 calcium, 47.6 sodium, 48.5 sulfate, 41.9 chloride, 126.3 bicarbonate. The ratio is 1.16 (balanced), but the important number is the residual alkalinity of 91.0, which is high and suits brown and porter grists. That alkalinity is deliberate: dark roasted malts are strongly acidic, and without carbonate to push against them the mash pH drops too far and the beer turns thin and sour rather than round.

Note the calcium in that stout is 43.9 ppm, just below the usual 50 ppm floor. That is a real trade-off rather than an error: adding more calcium would drag the residual alkalinity back down, which is the opposite of what the grist needs. Brewing water is a system of competing targets, not a checklist, and the calculator shows all of them at once so the trade-off is visible rather than hidden.

Calcium (50 to 150 ppm) is the workhorse. It supports enzyme activity in the mash, helps yeast flocculate, aids protein coagulation in the boil, and drops mash pH by reacting with malt phosphates. Below 50 ppm the mash and the fermentation both suffer; above 150 there is no further benefit and the water starts tasting mineral.

Sulfate and chloride are the flavour pair. Sulfate accentuates hop bitterness and dries the finish; chloride enhances malt sweetness and fullness. It is the ratio between them, not the absolute levels, that shapes perception, though sulfate above about 350 ppm turns harsh and chloride above roughly 200 ppm can read as flabby.

Sodium (under about 150 ppm) rounds and sweetens in small amounts and tastes salty above that. It usually arrives as a by-product of baking soda rather than as a deliberate addition.

Residual alkalinity measures how much the water resists the acidity of the malt; the formula section above explains how this calculator's figure is computed. Pale grists want it near or below zero; dark roasted grists want it high, because they bring their own acid. Getting this wrong is the single most common water mistake, and it shows up as a mash pH outside the 5.2 to 5.6 range where conversion and flavour both work best.

One warning: chalk barely dissolves in water. The figures here assume full dissolution, which does not happen in a mash without dissolved CO2 to help it. Most brewers use pickling lime or baking soda instead when alkalinity is genuinely needed. Treat any result relying on chalk as an upper bound on what you will actually get.

This calculates the ion profile of the finished water. It does not predict mash pH, and the two are not the same thing. Mash pH depends on the grist (how much of it is base malt, crystal, roasted or acidulated) as much as on the water, and predicting it requires a full mash model with malt buffering data. Residual alkalinity tells you which direction the water pushes; only a pH meter tells you where the mash actually landed.

Chalk is modelled at 100% dissolution and will not achieve that in practice. Pickling lime and baking soda are the practical alternatives when alkalinity is needed, and both are handled here.

The salt additions are applied to the whole batch volume as a single figure. Many brewers split additions between the mash and the sparge, or treat only the mash water, and the effective concentration in each is then different from the batch-average figure shown. If you are splitting, run the mash volume and the sparge volume as separate calculations.

Finally, a water report is a snapshot. Municipal supplies vary seasonally, sometimes substantially, and utilities blend sources through the year. If your source water is entering a recipe you care about, either request a recent report, test it yourself, or do what most brewers eventually do and build from reverse osmosis, where the starting point is zero and nothing changes between batches. That predictability is worth more than the specific profile.

The Homebrew ABV & Priming Sugar Calculator covers the other end of the same brew day, from original and final gravity through to the priming sugar for a target carbonation. The Coffee-to-Water Brew Ratio Calculator applies a similar ratio-driven approach to the other drink where water chemistry quietly decides the result. The bicarbonate and alkalinity side of brewing water is the same carbonate chemistry an aquarium keeper uses to estimate dissolved CO₂ from pH and carbonate hardness, which is what the Aquarium CO₂ Calculator does. And the Baker's Percentage Calculator uses the same proportional thinking for the other craft where a few grams either way changes the result.