Why calcium is expressed calcium carbonate in titrimetric analysis of calcium in water?

In titrimetric analysis of calcium in water, calcium is expressed as calcium carbonate (CaCO₃) because it provides a standardized way to report calcium concentrations based on a common compound. This expression allows for the conversion of calcium ion concentrations into a form that can be easily related to water quality standards and guidelines. Additionally, calcium carbonate is a stable and widely recognized compound, facilitating consistent comparisons across different studies and applications.