Water Mineral Calculator
Start with distilled or RO water, add a little Epsom salt for hardness and baking soda for alkalinity, and brew with water you control. Pick a target and see exactly how much to add.
Your water
0.1 to 20 litres of finished brew water.
0 to 300. Set with magnesium sulfate.
0 to 150. Set with baking soda.
2.46 g/L is about 1000 ppm GH.
1.68 g/L is about 1000 ppm KH.
1 L · GH 68 · KH 40 ppm
Add these stock amounts
- Magnesium sulfate (Epsom salt)
- 68.1 mL
- of 2.46 g/L stock (0.17 g salt)
- Sodium bicarbonate (baking soda)
- 40 mL
- of 1.68 g/L stock (0.07 g salt)
Pour these into a clean container, then top up with distilled or RO water to 1 L and stir.
What ends up in the water
- Magnesium
- 16.5 mg/L
- Sulfate
- 65.3 mg/L
- Sodium
- 18.4 mg/L
Added salts total about 235 mg/L. Ions are calculated from your GH and KH; they are not measured.
Making the stock solutions
- Epsom salt stock: dissolve 1.23 g in distilled water, up to 500 mL.
- Baking soda stock: dissolve 0.84 g in distilled water, up to 500 mL.
Use separate, labelled bottles. Never mix the two stocks together, and keep them in the fridge for a few weeks at most.
Safety
- Use food-grade or pharmaceutical-grade Epsom salt and baking soda, not garden, bath or cleaning products.
- Never drink a stock concentrate. Only drink the finished, diluted water.
- Start from distilled or RO water with near-zero minerals. Tap water adds its own minerals on top.
- This is general information, not medical advice. If you have kidney disease, are on a low-sodium diet, or are pregnant, ask your doctor before drinking remineralised water daily.
GH shapes extraction
General hardness (here from magnesium) helps water pull flavour out of the coffee. Too little tastes thin, too much can taste harsh and scales machines.
KH sets the buffer
Alkalinity (KH) buffers acidity. Too much mutes the brightness of the coffee, too little makes the cup sharp and unstable.
Safe by design
The calculator refuses GH above 300 ppm, KH above 150 ppm and volumes above 20 L. Use food-grade salts and never drink the stock concentrates.
How the numbers are worked out
GH and KH are both given in ppm (mg/L) as calcium carbonate (CaCO3), the same convention the SCA water standard and Barista Hustle use. Each salt is converted by comparing equivalents, not mass.
| Salt | Molar mass | Formula | Per 1 ppm |
|---|---|---|---|
| Epsom salt, MgSO4·7H2O (GH) | 246.47 g/mol | 246.47 ÷ 100.09 | 2.462 mg |
| Baking soda, NaHCO3 (KH) | 84.007 g/mol | 84.007 × 2 ÷ 100.09 | 1.679 mg |
- One magnesium ion carries two charges, like one CaCO3, so Epsom salt is converted one to one by moles.
- One bicarbonate ion carries one charge, half of a CaCO3, so it takes twice the moles per ppm of alkalinity.
- A stock solution at 2.46 g/L Epsom salt or 1.68 g/L baking soda is about 1000 ppm, so 1 mL per litre of final water adds about 1 ppm. You can use any strength between 0.1 and 50 g/L.
- Rounding: salt masses to 0.01 g, stock volumes to 0.1 mL, ions to 0.1 mg/L. Below about 0.05 g the tool suggests stock solutions, because most kitchen scales cannot weigh that reliably.
- Assumptions: the starting water has no minerals, the salts are pure and fully dissolved, and all hardness comes from magnesium. The SCA standard defines hardness mostly through calcium, so this is a simplified, magnesium-only version of it. Tap water, bottled water and calcium sources are not modelled.
- The sodium and sulfate figures are calculated from your targets. They are not measured, so verify with a test kit or TDS meter if it matters to you.
Presets
- SCA standard target: GH 68 ppm, KH 40 ppm. Target of the 2009 SCA brewing water standard: hardness 68 mg/L, alkalinity about 40 mg/L. Its acceptable hardness range is 17-85 mg/L.
- Barista Hustle Recipe 4: GH 80 ppm, KH 40 ppm. A balanced recipe from Barista Hustle's DIY water recipes: GH 80, KH 40 ppm.
Sources
- Barista Hustle, DIY Water Recipes Redux (2.45 g/L Epsom salt and 1.68 g/L baking soda concentrates, 1000 ppm each).
- Barista Hustle, The Water Course: Remineralisation.
- Specialty Coffee Association, Water Quality Handbook, and the 2009 SCAA brewing water standard (hardness 68 mg/L, alkalinity about 40 mg/L, pH 6.5-7.5, TDS 150 mg/L).
Water ready?
The Recipe Builder sets dose, water, grind, and temperature for your brewer and roast.