High levels of hard-water ions such as Ca2+and Mg2+can cause scaly deposits in plumbing, appliances, and boilers. These two ions also combine chemically with soap molecules, resulting in decreased cleansing action. The American Water Works Association indicates that ideal quality water should not contain more than 80 mg/L of total hardness as CaCO3. High levels of total hardness are not considered a health concern. On the contrary, calcium is an important component of cell walls of aquatic plants, and of the bones or shells of aquatic organisms.
Magnesium is an essential nutrient for plants, and is a
component of chlorophyll.