Water hardness
What is water hardness in coffee?
Water hardness is the amount of dissolved minerals, mainly calcium and magnesium, in your water. Some minerals help extract flavour, but very hard water makes coffee taste flat and chalky and leaves limescale, while very soft water can taste thin. A simple jug filter is often enough to improve hard tap water.
Hardness varies a lot by region: much of south and east England has hard water, while Scotland, Wales and the north-west are generally soft. The Specialty Coffee Association publishes target ranges for brewing water.