For hot drinks, the optimal water hardness is approx. 8 degrees dH. Harder water affects the development of the aroma while softer water leads to a bitter taste.
For optimal results, the water should neither be too soft nor too hard during coffee preparation. A range of between 8 and 12 degrees dH is considered ideal. With hard water, the fine acid of the coffee is neutralized and the coffee tastes flat. The longer the contact time between the water and coffee powder, the stronger this effect is and so coffee with a flat taste and little flavour is obtained. Soft water with a hardness degree of below 5 degrees dH can also negatively influence the taste of coffee. Changes in the swelling behaviour of the coffee powder may result. Excessive extraction leads to a high acid content and increased bitterness of the coffee. In order to keep the capacity of your coffee machine at an optimal level, regular descaling is recommended.
For tea, water with 8 to 10 degrees dH is considered ideal. A high level of calcium carbonate in hard water forms a distasteful film on the tea surface together with the ingredients in the tea. This influences the colour of the tea (gets cloudy) and binds with more bitter substances, which gives the tea an unpleasant ‘furry’ taste. With soft water, the same tea can have a much better, fuller aroma, than it can develop with hard water. This applies in particular to white & green teas and Darjeeling tea brands containing fewer tannins, while Assam and Ceylon teas react less sensitively to hard water.