Total hardness in water is primarily due to calcium, magnesium, and which other component?

Total hardness in water is primarily due to the presence of multivalent cations, particularly calcium and magnesium, which are the main contributors. However, hardness can also include other cations that have a similar impact, such as strontium and barium. These cations are all capable of forming insoluble compounds with carbonate ions and contribute to the overall hardness of water.

The choice of "all multivalent cations" encompasses not only calcium and magnesium but also other divalent and trivalent metals that can affect water hardness. Understanding this helps clarify that hardness is not strictly limited to just calcium and magnesium but includes these additional cations, making it a broader category.

Other options like iron and nitrate do not typically contribute to water hardness in the same way. Multivalent cations are specifically defined by their charge and ability to contribute to hardness, which is a critical concept when evaluating water quality and treatment needs.