In domestic water well supplies, which two elements cause the majority of hardness?

Hardness in water is primarily caused by the presence of certain minerals, specifically calcium (Ca) and magnesium (Mg). When water percolates through soil and rock, it can dissolve minerals, leading to the introduction of these elements into the water supply. Calcium and magnesium ions are the most common contributors to water hardness, and their solubility in water is significant, particularly in limestone and dolomite formations.

Calcium is often found in water in the form of calcium carbonate (CaCO3), while magnesium typically appears as magnesium carbonate (MgCO3). The levels of these elements can greatly influence the quality of water and its suitability for various uses, such as drinking, cooking, and industrial processes. High concentrations of calcium and magnesium can lead to scaling in pipes, difficulty in soap lathering, and other water quality issues.

In contrast, other elements, like sodium (Na) and zinc (Zn), do not significantly contribute to water hardness. Sodium, for instance, is primarily associated with water salinity rather than hardness. Therefore, the pairing of calcium and magnesium as the leading causes of hardness in domestic water supplies is accurate and reflects the common understanding of water chemistry.