The water across the country varies greatly and the water will have a direct affect on the taste of the beer. Hardness, which is composed of calcium and magnesium ions has to be considered. Many brewers like the water to contain at least 50 mg/l of Calcium, but too much can be detrimental to the flavors because it lowers the pH of the mash. Similarly, a little Magnesium is good, but too much can create a bitter taste. 10 to 25 mg/l of manganese is most desirable.