The importance of water to have the best taste has a scientific basis. Water not only plays the role of a solvent with no flavour, but it also plays an important role in the final product.
The best water must have little or no chlorine because the compounds have a strong oxidizing power that develops above all when hot and acts on the fats and on the formation of the cream. The absence of ammonia, sulphur compounds, and ferruginous or odours derived from algae or moulds and a hardness related above all to the presence of calcium salts and magnesium.
For a good coffee, you do not need distilled or demineralized water because the presence of calcium salts gives the coffee more flavour. For this reason, a high hardness improves the quality, also because the calcium gives body, and allows the formation of an elastic and stable cream. The best coffees are obtained with moderately hard, alkaline waters, partially or devoid of magnesium salts with a bitter taste. Get that?
Calcium is good for coffee, but not as good for machines that, due to high temperatures, favour the formation and deposition of salts inside. Therefore, filter your water to eliminate the impurities and to reduce slightly the presence of mineral salts. Then allow the water to settle in an open container, in the refrigerator, in order to make the chlorine disappear. And that’s the best water for your coffee.