What primarily contributes to water hardness?

Water hardness is primarily caused by the presence of dissolved minerals, specifically calcium and magnesium ions. When water percolates through soil and rock formations, it can dissolve these minerals, leading to hard water. This dissolved calcium and magnesium form complexes that contribute to the hardness levels measured in water.

In many applications, such as brewing, water hardness is an important factor to consider because it affects the extraction of flavors from ingredients and can influence the solubility of various compounds, which ultimately impacts the final product's taste and quality.

In contrast, the other options involve elements or compounds that do not contribute to water hardness. Iron and sulfur are associated with different kinds of water quality issues, while sodium and potassium are typically found in soft water, where they are used in water softening treatments. Chlorine and fluoride, on the other hand, are commonly found in treated drinking water for disinfection and dental health, respectively, but they do not play a role in determining water hardness.