What does a hardness test measure in water?

A hardness test specifically measures the concentration of calcium and magnesium ions in water. These two minerals are the primary contributors to water hardness. When water is considered "hard," it has a high level of these ions, which can lead to scale buildup in pipes and appliances and affects soap's ability to lather.

Understanding water hardness is crucial in water treatment processes and for household applications. Water softening processes commonly target the removal or reduction of calcium and magnesium to prevent scale formation and improve the effectiveness of soaps and detergents.

The other options refer to different parameters: the concentration of iron and lead relates to heavy metals, while chlorine concentration pertains to disinfection, and sodium concentration is often a consideration in the context of salinity. Each of these measurements serves a distinct purpose, but they do not pertain to the measurement of water hardness.