Which two elements are the main causes of water hardness?

Water hardness is primarily caused by the presence of certain dissolved minerals, with calcium (Ca) and magnesium (Mg) being the two most significant contributors. When water percolates through rocks and soil, it can dissolve these minerals, leading to an increase in hardness levels.

Calcium and magnesium ions can form complexes with soap and other cleaning agents, reducing their effectiveness and creating scale in pipes and appliances. Testing for hardness typically involves measuring the concentrations of these two elements in water. Therefore, the presence of high levels of calcium and magnesium is directly associated with the hardness of water, making them the main causes in this context.

Other options consist of elements that do not primarily contribute to water hardness. Nitrogen and phosphorus (from the first choice) are nutrients but not hardness contributors. Iron and aluminum (from the third choice) can affect water quality but are not classified as hardening agents. Sodium and potassium (from the fourth choice) are also not responsible for hardness and are often associated with different water quality issues. This highlights the vital role that calcium and magnesium play in the hardness of water.