Glossary Of Water Treatment Industry Terms . . . "H"
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
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).
head loss - The
same as "pressure drop".
- A dry solid, largely calcium hypochlorite, used as a disinfecting
agent; has excellent stability as long as kept dry.
home-owned - A
slang term sometimes applied to permanently installed household water
conditioning equipment, as opposed to rental or portable exchange equipment.
hydration - The
chemical combination of water into a substance.
hydraulic - Referring
to water or other fluids in motion.
- 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.
- 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. (See pH.)
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.
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.Dust, smoke from industry, carbon dioxide, spores and smog may be absorbed by water droplets. Water is sometimes known as the universal solvent. It has a tendency to dissolve a little bit of everything it touches. For example, if it dissolves sulfur from industrial smokestacks, it can form acid rain. This increases its capacity to dissolve other substances. The water vapor in clouds eventually condenses and falls back to earth as rain, sleet, hail or snow.
After reaching the ground, water continues to dissolve additional matter it contacts. As water runs over the surface, it can become cloudy, even muddy. Then, as water seeps down through the ground, it may dissolve a little bit of the minerals and substances that could be present, such as calcium, magnesium, iron, or radioactivity.
By the time water returns to rivers, lakes, reservoirs,
or underground aquifers, it may have accumulated amounts of the elements
it has contacted. Along the way bacteria, chemicals, agricultural byproducts,
fertilizers, insecticides, and other man made wastes may also have entered
the picture and become dissolved in the water. (See transpiration.)
hydrolysis - The
reaction of a salt with water to form an acid and a base.
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.
hydroxide - A chemical
compound containing hydroxyl (OH) ion. (See hydroxyl.)
hydroxyl - The OH
anion which has a single negative charge, and provides the characteristics
common to bases. (See base.)
hypochlorite - The OCL anion; calcium and sodium hypochlorite are commonly used as bleaches and disinfecting agents.