total hardness of 50-175 ppm CaCO3 (2,9-9,8 dH°)
carbonate hardness of 40-75 ppm CaCO3 (2,9-9,8 dH°)
total hardness should exceed carbonate hardness
pH of 6.5-8
Brew water containing low levels of both calcium ions and bicarbonate (HCO₃⁻) – that is, soft water – will result in a highly acidic cup, sometimes described as sour. Brew water containing high levels of HCO₃⁻ – typically, hard water – will produce a chalky cup, as the bicarbonate has neutralized most of the flavorsome acids in the coffee.