Hard Water - water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.
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.
Hardness Leakage - the presence of a consistent concentration of hardness in the effluent from an ion exchange water softener, often due to high concentrations of hardness or sodium in the water being treated.
Head - a measure of the pressure at a point in a water system, expressed in pounds per square, or in the height of a column of water which could produce the pressure.
Head Loss - see pressure drop.
Hydraulic - referring to water or other fluids in motion.
Hydraulic Classification - a process in which particles pf the same specific gravity may be graded according to size by backwashing or other relative upward flow of water, with the smallest particles tending to rise to the top of the bed, and the largest particles tending to sink to the bottom, because of variations in weight to surface area ratios.
Hydrogen Cycle - the cation exchange cycle in which the cation exchanger is regenerated with acid, and cations are removed from the solution treated, in exchange for hydrogen ions.
Hydrogen Ion Concentration - the concentration of hydrogen ions in moles per liter of solution; often expressed as ph.
Hydrologic Cycle - the water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere.
Hydrolysis - the reaction of a salt with water to form an acid and a base.
Hydroxide - a chemical compound of an element or elements with the hydroxyl (oh) anion.
Hypochlorite - the "OCI" anion,; calcium and sodium are commonly used as disinfecting agents