Reference · water recipes

DIY coffee water: brewing water from distilled water and minerals

Start with nearly empty water, then add back a little magnesium (hardness) and a little bicarbonate (alkalinity). Two concentrates and a 0.01 g scale get you to the Specialty Coffee Association’s brewing-water targets. Below: the targets, published recipes as written, and the arithmetic.

Updated 2026-10-17 · sources listed at the end · chemistry here is for flavor; this page makes no health claims

The targets, and where SCA summaries disagree

The full SCA Water Quality Handbook (2018, by Marco Wellinger, Samo Smrke and Chahan Yeretzian of ZHAW) is a paid book, so the figures below come from summaries you can open. They do not all agree.

The hardness row is where summaries split: Prima Coffee’s 2021 table says only “Hardness,” Pentair’s brochure says total hardness of 17–85 mg/L, and an SCA study guide calls the same 17–85 calcium hardness (citing the SCAA standard revised November 2009). The 2021 home-brewer standard asks for calcium hardness of 50–175 ppm as its summary of “the current SCA Water standard.” A recipe aimed at about 68 ppm hardness and 40 ppm alkalinity sits inside both the 2009 range and Wellinger’s 40–250 window.

What each mineral does

• Hardness (magnesium, calcium). Total hardness is the sum of the calcium and magnesium in the water. In Wellinger’s SCA article, hardness had an insignificant effect on extraction efficiency between 20 and 250 ppm CaCO₃.
• Alkalinity (bicarbonate). Alkalinity is the water’s capacity to neutralize acid. Wellinger writes that its effect on perceived acidity is “several hundredfold times higher than that of pH,” so high-bicarbonate water mutes a coffee’s acidity; average U.S. tap water, he notes, carries about 150 ppm. Bicarbonate hardness is “temporary”: boiling drives it out as scale.
• Sodium arrives with baking soda. In the University of Bath work summarized by Phys.org, sodium-rich (softened) water did not improve taste.

The research disagrees on magnesium. In 2014 Hendon, Lesley Colonna-Dashwood and Maxwell Colonna-Dashwood used density functional theory to calculate how strongly magnesium, calcium and sodium bind to coffee acids, caffeine and eugenol; Phys.org quoted Hendon that “high magnesium ion levels increase the extraction.” Prima Coffee’s 2024 review notes the study brewed no coffee, and cites a 2021 Umeå University study (Bratthäll) that found no substantial change in lactic, malic or citric acid extraction at about 100 ppm magnesium or calcium.

Units: what “ppm as CaCO₃” means

Hardness and alkalinity are both reported as the calcium carbonate that would carry the same charge. Per Wikipedia’s hard-water article, 1 mmol/L of hardness equals 100.09 mg/L CaCO₃, and one grain per U.S. gallon equals 17.118 ppm, so the SCAA’s “4 grains” is 4 × 17.118 = 68.5 ppm. Bicarbonate carries one charge rather than two, so each millimole counts as half a millimole of CaCO₃. To convert a tap-water report from grains, German degrees or mmol/L, use the water hardness converter.

The two-concentrate method

Barista Hustle’s recipes use two stock solutions, each made by dissolving one salt in 1 liter of deionized or distilled water, and each designed to be about 1,000 ppm as CaCO₃:

Checking those strengths with molar masses from the chemistry references (NaHCO₃ 84.006 g/mol, MgSO₄·7H₂O 246.47 g/mol, CaCO₃ 100.0869 g/mol):

Both land within 0.5% of 1,000. (A Barista Hustle reply gives 1.20 g if your magnesium sulfate is anhydrous: at 120.366 g/mol, 998 ppm.)

Published recipes, as written

Barista Hustle’s 2019 table gives each recipe in grams of buffer (A), hardness concentrate (B) and water, totaling 1,000 g. The ppm columns are this page’s arithmetic (grams of concentrate ÷ 1,000 × the strengths above); the page itself states targets only for Budapest (40 alkalinity, 51 hardness) and cites the SCA hardness range of 17–85.

* Computed here, ppm as CaCO₃.

Barista Hustle calls Rao Water “close to Scott Rao’s recommended water chemistry.” Five rows fall inside the 2009 SCAA hardness range of 17–85; Melbourne is among them but below Wellinger’s 40 ppm floor, and the last three exceed 85.

That sodium figure is above the SCAA’s “at or near 10 mg/L,” because baking soda is the only alkalinity source in this method; a recipe hitting 40 ppm alkalinity with baking soda alone cannot also meet that sodium target.

A volume-measured version

Whole Latte Love’s 2020 method uses spoons: ½ teaspoon baking soda in 1 L distilled water (buffer), 2¼ teaspoons Epsom salt in another liter (hardness); then, per gallon of distilled water, pour off 1 cup (250 mL) and add 63 mL hardness and 185 mL buffer concentrate. It says the result falls within SCA ranges but gives no ppm figures or teaspoon weights, so its strength cannot be checked from the page.

Step by step (gram method)

1. Buy food-grade Epsom salt and baking soda, plus distilled or deionized water.
2. Weigh 1.68 g baking soda into a clean 1 L bottle, top to 1,000 g with distilled water, shake until clear. Label it “A, buffer.”
3. Weigh 2.45 g Epsom salt into a second bottle, top to 1,000 g, dissolve. Label it “B, hardness.”
4. Tare an empty jug. Add the recipe’s grams of A, then B, then distilled water to 1,000 g.
5. Brew, taste, and change one concentrate at a time.

Food-safety and handling checklist

• ☐ Food-grade salts only. A Barista Hustle reply says “Definitely use food grade” Epsom salt. U.S. rules list magnesium sulfate heptahydrate and sodium bicarbonate as GRAS food ingredients meeting Food Chemicals Codex specifications (21 CFR 184.1443, 184.1736); check that the label says food grade.
• ☐ Baking soda, not baking powder. Baking powder contains acids as well as bicarbonate.
• ☐ Clean, odor-free containers and a 0.01 g scale (Barista Hustle).
• ☐ Storage: replies on the Barista Hustle post suggest keeping concentrates in the dark, refrigerated, and using them within a month (a week at room temperature).
• ☐ Not for espresso machines unless you know the equipment’s needs: Barista Hustle warns against it, and a reply notes these calcium-free recipes raise corrosion concerns.
• ☐ Don’t trust a TDS pen for these blends. Barista Hustle notes meters assume a typical tap-water ion mix.

Distilled water: avoid it, or build on it?

The National Coffee Association advises avoiding distilled or softened water, and the SCA cupping protocol says the same. Both mean brewing with it as is; the recipes above use distilled water only as a blank base and add minerals back. For temperature and reading your tap-water report, see water temperature & chemistry.