Alkalinity — in practice, bicarbonate — is the buffering capacity of water: its ability to resist changes in pH.
It is the most under-discussed variable in brewing water and one of the most consequential.
What it does to the cup
Coffee’s brightness comes from organic acids. Bicarbonate neutralises them.
High-alkalinity water therefore takes a coffee with lovely malic and citric acidity and flattens it. The brew is not badly extracted — the acids are there and they have been buffered away. It tastes dull, chalky and muted.
Low-alkalinity water lets the acidity through, and a bright Kenyan tastes bright.
Why it explains confusing results
Two waters with the same total hardness can behave completely differently depending on their bicarbonate. That is why “my water is 120 ppm and my coffee is flat” is a real complaint with a real answer.
What to aim for
Low. Under about 50 mg/l of bicarbonate is comfortable. The SCA target is around 40.
How to lower it
A carbon and ion-exchange filter reduces it somewhat.
Mineral recipes control it directly, which is much of why competition brewers use them.
Not a softener — ion exchange swaps calcium for sodium and leaves bicarbonate largely intact, so you keep the flat taste and add saltiness.
Measuring it
A drop test kit for alkalinity costs very little and tells you far more than a TDS meter.
Last reviewed 8 August 2026