Water is not a neutral solvent. Its mineral content changes both what dissolves and how the result tastes.
Magnesium
The most useful. Magnesium ions bind readily to coffee’s flavour compounds and carry them into solution, and they are particularly associated with bringing out fruit and brightness.
Water with useful magnesium extracts more, and more interestingly, than water without.
Calcium
Also extracts, less selectively, and associated with body rather than brightness. Calcium is also half of what forms limescale.
Bicarbonate — the one to keep low
Bicarbonate buffers acidity. High-bicarbonate water neutralises the acids that give a coffee its brightness, so the cup reads as flat and dull however well you brewed it.
It is also the other half of limescale.
This is why two waters with identical total hardness can behave completely differently: what matters is the split between hardness and alkalinity.
Targets
Roughly 50 to 150 ppm total, with bicarbonate low — under about 50 mg/l.
The SCA publishes a more detailed target profile, and hitting it exactly matters far less than being roughly in range.
In practice
Filtered tap water gets most people close. Mineral recipes dosed into distilled water give complete control and are a real commitment.
Last reviewed 8 August 2026