Free Brewing Tool
What's in your brewing water?
Water is roughly 98 percent of every cup, and its minerals decide how much flavor you extract. Pull three numbers from your tap-water report (often published by your water utility) or a bottled-water label, and this calculator converts them into total hardness and alkalinity, then compares them with the Specialty Coffee Association targets.
mg/L, from the water report
mg/L, from the water report
mg/L, sometimes listed as alkalinity
Don't have your numbers yet? Find your water report
US water utilities publish an annual water quality report (a Consumer Confidence Report). Enter your city and state and we'll link you straight to a search for yours, or look your tap water up by ZIP code in the EWG database.
Total Hardness
Calculated as (2.5 x calcium) + (4.1 x magnesium). SCA target: 50-175 mg/L as CaCO3, lower-middle preferred.
Alkalinity
Calculated as bicarbonate x 50/61. SCA target: about 40 mg/L as CaCO3, up to ~75 acceptable.
Worked examples
Two real-world readings, run through the same math this calculator uses.
A balanced city tap water
Hardness lands at 70.5 mg/L and alkalinity at 49.2 mg/L as CaCO3, comfortably inside the SCA windows with alkalinity near the 40 mg/L target.
A mineral-heavy bottled water
Hardness is 141 mg/L, inside the SCA range, but alkalinity reaches 98.4 mg/L, well past the ceiling. The cup would taste dull, so dilute or switch to a lower-bicarbonate water.
Why calcium and magnesium taste so different
Calcium and magnesium both carry hardness, but they extract different flavor compounds. Calcium is heavier and less mobile: it pulls denser, caramelized compounds out of the grounds, which boosts body and sweetness. Cups brewed with calcium-forward water feel rounder and richer, and sweet notes read more clearly.
Magnesium is lighter and more aggressive in solution. It latches onto fruity and acidic compounds, lifting them into the cup, which is why magnesium-forward water tastes brighter and juicier. Two waters with identical hardness numbers can taste very different depending on how that hardness is split between calcium and magnesium.
Alkalinity, meanwhile, is the buffer. Bicarbonate neutralizes coffee acids as they dissolve, and a little buffering makes acidity taste sweet and controlled. Too much and the cup goes flat and chalky; too little and bright coffees turn sharp and sour. That is why the SCA targets hardness as a range but alkalinity as a specific number, around 40 mg/L as CaCO3.
Water Recipe Card
Enter your three numbers to unlock a downloadable recipe card
Once your calcium, magnesium, and bicarbonate readings are in, you can email yourself a printable card with your numbers and personalized recommendations.
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