Water hardness refers to the total content of alkaline earth ions, including Calcium, Magnesium, Strontium, and Barium. However, since the concentration of Ca²⁺ and Mg²⁺ is typically much higher than that of other alkaline earth ions, hardness is considered virtually equal to the sum of the concentrations of these two ions.

This test measures water hardness through titration, a method that involves the controlled addition of a reagent to the sample until a endpoint is reached, indicating the concentration of the ions present. This procedure is essential for obtaining accurate and reliable results.

Water hardness is commonly expressed in milligrams of calcium carbonate per liter (mg/L CaCO3), equivalent to ppm CaCO3. Measuring hardness is important as it affects water quality, its use in agriculture, and can influence crop health, the effectiveness of fertilizers, and the operation of irrigation systems.