The hardness of water is estimated by:

The total hardness of a water sample (caused predominantly by ${\text{Ca}}^{2+}$ and ${\text{Mg}}^{2+}$ ions) is standardly estimated via complexometric titration using EDTA (Ethylenediaminetetraacetic acid) as a chelating agent and Eriochrome Black T (EBT) as an indicator. While this is a titrimetric procedure, it is explicitly known as the EDTA method due to the specific complexing agent used.