Hard water
Water's hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are positively charged metal complexes with a charge greater than 1+. Usually, the cations have the charge of 2+. Common cations found in hard water include Ca and Mg. These ions enter a water supply by leaching from minerals within an aquifer. Common calcium-containing minerals are calcite and gypsum. A common magnesium mineral is dolomite (which also contains calcium). Rainwater and distilled water are soft, because they contain few ions.
Hardiness (psychological)
There are several instrument developed to measure hardiness, the most frequently used being the Personal Views Survey, the Dispositional Resilience Scale, and the Cognitive Hardiness Scale. In addition to these, other scales based on hardiness theory have been designed to measure the construct in specific contexts and in special populations, such as for example parental grief and among the chronically ill.