How is water hardness commonly expressed?

Water hardness is commonly expressed in terms of calcium carbonate (CaCO3) concentration. The reason for this is that calcium and magnesium ions primarily contribute to water hardness, and the standard practice is to report the hardness levels in terms of equivalent calcium carbonate. Calcium carbonate provides a clear, consistent basis for quantifying water hardness because it denotes the combined effect of both calcium and magnesium ions on water quality.

Reporting hardness as calcium carbonate allows for straightforward comparisons and adherence to regulatory standards, making it easier to manage and treat water supplies effectively. This standardization is vital for informing decisions regarding water treatment processes and assessing the potential impacts of hard water on plumbing and appliances.

Therefore, expressing water hardness in mg/l as calcium carbonate is the correct and widely accepted method in water quality assessment.