Which ions are primarily responsible for water hardness?

Water hardness is primarily attributed to the presence of calcium and magnesium ions in the water. These two cations are the most significant contributors to the overall hardness level, which is a measure of the concentration of divalent cations in water. When water passes through or over limestone, gypsum, or other mineral-rich deposits, it dissolves these minerals, releasing calcium and magnesium into the water.

The hardness of water is important because it can affect various aspects of water use, including its taste, its interaction with soaps and detergents, and its potential scaling in pipes and appliances. In contrast, other ions such as sodium and potassium, while they can impact the taste and other characteristics of the water, are not the primary contributors to hardness. Similarly, chloride and sulfate ions, along with bicarbonate and nitrite, do not play a significant role in determining water hardness. Thus, the correct response identifying calcium and magnesium accurately reflects the chemistry of water hardness and its implications in drinking water systems.