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Hardness |
A characteristic of natural
water due primarily to the presence of dissolved polyvalent (valence
greater than 1) cations, such as calcium (Ca+2) and magnesium (Mg+2).
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. |
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Head |
A measure of the pressure
at a point in a water system, expressed in pounds per square inch, or in
the height of a column of water which would produce the pressure. 1 psi
equals 2.31 feet of head (water). |
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Head Loss |
The same as "pressure
drop". |
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Health Advisory |
An EPA document that
provides guidance and information on contaminants that can affect human
health and that may occur in drinking water, but which EPA does not
currently regulate in drinking water. |
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High-Test Hypochlorite |
A dry solid, largely
calcium hypochlorite, used as a disinfecting agent; has excellent
stability as long as kept dry. |
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Home-Owned |
A slang term sometimes
applied to permanently installed household water conditioning equipment,
as opposed to rental or portable exchange equipment. |
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Hydration |
The chemical combination of
water into a substance. |
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Hydraulic |
Referring to water or other
fluids in motion. |
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Hydraulic Classification |
A process in which
particles of 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 largest particles
tending to sink to the bottom, because of variations in weight to sur area
ratios. |
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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. |
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Hydrogen Ion
Concentration |
The concentration of
hydrogen ions in moles per liter of solution; often expressed as pH. (See
pH.) |
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Hydrogen Sulfide |
This is not a routine test
but is determined only upon request and on a separate special sample. It
is a poisonous gas and will cause headache and nausea. It smells like
"rotten eggs". It causes a black precipitate with many metals. |
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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. Water evaporates from the earth and rises into the
atmosphere where it forms clouds. In nature, this is where water is in its
purest form. However, it does not stay that way for long. Its stay in the
air is short. Water droplets forming in clouds, absorb particles and
impurities found floating in the air. |
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Hydrolysis |
The reaction of a salt with
water to form an acid and a base. |
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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. |
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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. |
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Hydroxide |
A chemical compound
containing hydroxyl (OH) ion. (See hydroxyl.) |
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Hydroxyl |
The OH anion which has a
single negative charge, and provides the characteristics common to bases.
(See base.) |
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Hypochlorite |
The OCL anion; calcium and
sodium hypochlorite are commonly used as bleaches and disinfecting agents. |
