Hard Water

water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.

Definitioner

Total Hardness: the sum of all hardness constituents in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to the calcium and magnesium in solution, but may include small amounts of metals such as iron which can act like calcium and magnesium in certain reactions.
Hardness: a characteristic of natural water due to the presence of dissolved calcium and magnesium; water hardness is responsible for most scale formation in pipes and water heaters, and forms insoluble" curd" when it reacts with soaps. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent.
Grain Per Gallon: (gpg) a common basis for reporting water analyses in the U.S. and Canadaone grain per U.S. gallons equals 17.12 milligrams per liter or parts per million. one grain per British gallon equals 14.3 milligrams per liter or parts per million.
Grain: (gr.) a unit of weight equal to 1/7000th of a pound, or 0.0648 gram.
Carbonate: the Co3- ion.
Calcium: one of the principal elements making up the earths crust, the compounds of which make the water hard. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are a means of clearly identifying hard water.