A cup of coffee is mostly water.
Two numbers describe most of what your water brings to the cup. Hardness (GH) is the magnesium and calcium in it: the harder the water, the more it pulls out of the grounds. Alkalinity (KH), or buffer, is the bicarbonate that neutralises acids. Both are measured in ppm as calcium carbonate.
Each one is made so it measures about 1000 ppm. Use distilled or deionised water and a scale accurate to 0.01 g.
- Buffer (alkalinity): dissolve 1.68 g of baking soda (sodium bicarbonate, not baking powder) in 1 litre.
- Hardness: dissolve 2.45 g of Epsom salt (magnesium sulfate heptahydrate) in 1 litre.
The SCAA 2009 handbook specification.
- Buffer concentrate
- 40.1 g
- Hardness concentrate
- 68.6 g
- Distilled water
- 891.3 g
Weigh everything into one container on a scale (1 g of water is about 1 ml). Hardness outside 17–85 ppm is outside the SCA range.
Find “total hardness” in your water supplier's annual quality report and enter it here.
Recipes, concentrates and the SCA range: Barista Hustle: Barista water recipes (checked 7 November 2026). Unit conversions (grains per gallon, German degrees) are standard arithmetic.