Learn about the different types of contaminants that might put your family at risk.

hard water
Water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent. 
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.
A measure of the pressure at a point in the water system expressed in pounds per square inch or in the height of a column of water which would produce the pressure.
head loss
(See pressure drop.)
high-test hypochlorite
A dry solid, largely calcium hypochlorite [Ca (OH)2], used as a disinfecting agent; has excellent stability as long as kept dry.
The chemical combination of water into a substance.
Referring to water or other fluids in motion.
hydrogen ion concentration
The concentration of hydrogen ions in moles per liter of solution; often expressed as pH.
hydropneumatic system
A system utilizing both air and water in its operation, such as the pressure tank used with many well systems, which utilizes an air chamber to maintain pressure on the water when the pump is not operating.
hydrostatic test
A pressure test procedure in which a vessel or system is filled with water, purged of air, sealed, subjected to water pressure, and examined for leaks, distortion, and/or mechanical failure.
A chemical compound of an element or elements with the hydroxyl (OH) anion.
The “OH” anion which has a single negative charge and provides the characteristics common to bases.
Calcium and sodium hypochlorites (CLO2) are commonly used as bleaches and as disinfecting agents.