Why your brewing water matters more than you think
A cup of coffee is about 98% water, so the water you brew with is not a background detail — it is most of the drink. Get it wrong and even the best beans taste flat or harsh.
Hardness and minerals
Some minerals help water grab flavour from coffee, but too many, especially as scale, mute it and damage equipment. A moderate mineral content is the sweet spot.
What to use at home
Filtered tap water is fine for most people. If your tap water is very hard or heavily chlorinated, a simple filter jug makes an audible difference in the cup.