Which two elements are the main causes of hardness in water?

The main causes of hardness in water are calcium and magnesium. These two elements naturally occur in groundwater and surface water, often as a result of the dissolution of minerals such as limestone and dolomite. When water percolates through soil and rock, it can pick up these minerals, leading to increased concentrations of calcium and magnesium ions.

Hardness in water is primarily measured by the concentration of these ions. Hard water can lead to various inconveniences, such as scaling in pipes and appliances, which can affect their efficiency and longevity. Additionally, it can impact the performance of soaps and detergents, leading to less effective cleaning.

Sodium and potassium, while they may contribute to other water quality issues, are not typically associated with hardness. Bicarbonate and sulfate do influence the chemical composition of water, but they do not directly contribute to hardness. Iron and manganese can be problematic in water treatment due to staining and other issues but also do not induce hardness. Hence, the correct answer identifying calcium and magnesium directly relates to the defining characteristics of water hardness.