Water for brewing
A cup is 98 % water. Ignore it and everything else you tune is guesswork.
Brno tap water sits around 15 °dH. That is a lot: magnesium and calcium do pull sweetness out of coffee, but past a point they flatten it and the cup turns chalky.
What to look at
- Total hardness — aim for 50–90 mg/l as CaCO₃.
- Alkalinity (KH) — aim for 40 mg/l. More alkalinity buries the acids.
- Mg:Ca ratio — magnesium lifts fruit, calcium builds body.
The recipe we use
Into 5 l of distilled water: 0.4 g of magnesium sulfate and 0.17 g of sodium bicarbonate. That lands near 70 mg/l hardness and 40 mg/l alkalinity.
None of this is dogma. If you would rather not weigh salts, filtered water cut 1:1 with distilled gets you most of the way.