Absorption - The process in which one substance is
taken into the body of another substance, termed the
absorbent. An example is the absorption of water into
Acid - A substance which releases hydrogen ions when
dissolved in water. Most acids will dissolve the common
metals and will react with a base to form a neutral salt
Activated Carbon - A granular material usually produced
by the roasting of cellulose base substances, such as
wood or coconut shells, in the absence of air. It has a
very porous structure and is used in water conditioning
as an adsorbent of organic matter and certain dissolved
gases. Sometimes called “activated charcoal.”
Adsorption - The process in which matter adheres to
the surface of the adsorbent.
Aeration - The process in which air is brought into
intimate contact with water, often by spraying water
through air or by bubbling air through water. Aeration
may be used to add oxygen to the water for oxidation of
matter such as iron or to cause the release of dissolved
gases such as carbon dioxide or hydrogen sulfide from
Alkalinity - The quantitative capacity of a water or water
solution to neutralize an acid. It is usually measured by
titration with a standard acid solution of sulfuric acid and
expressed in terms of its calcium carbonate equivalent.
Anion - A negatively charged ion in solution such as
bicarbonate, chloride or sulfate.
Anion Exchange - An ion exchange process in which
anions in solution are exchanged for other anions from
an ion exchanger. In demineralization, for example,
bicarbonate, chloride and sulfate anions are removed
from solution in exchange for a chemically equivalent
number of hydroxide anions from the anion exchange
Aquifer - A layer or zone below the surface of the earth
which is capable of yielding a significant volume of water.
Atom - The smallest particle of an element that can exist
either alone or in combination with smaller particles of
the same element or of a different element.
Attrition - The process in which solids are worn down or
ground down by friction, often between particles of the
same material. Filter media and ion exchange materials
are subject to attrition during backwashing, regeneration
Backwash - The process in which beds of filter or ion
exchange media are subjected to flow opposite to
service flow direction to loosen the bed and to flush
suspended matter collected during the service run to
Bacteria - Unicellular micro-organisms which typically
reproduce by cell division. Although usually classed as
plants, bacteria contain no chlorophyll.
Bacteriostatic - A feature of a carbon filter that is
supposed to inhibit the growth of bacteria within the filter - usually by the addition of silver.
Base - A substance which released hydroxyl ions when
dissolved in water. Bases react with acids to form a
neutral salt and water.
Bed - The ion exchange or filter media in a column or
other tank or operational vessel.
Bed Depth - The height of the ion exchange or filter
media in the vessel after preparation for service.
Boiling Point - The temperature at which a substance
will change from a liquid state to a gaseous or vapor
Brackish Water - Water containing between 1000 and
1500 mg/l of dissolved solids is generally considered to
Brine (R.O.) - Same as reject water. One of two streams
of fluids generated by a reverse osmosis unit. It contains
the impurities removed from the feed water.
Brine (Softening) - A strong solution of salt(s), such as
sodium chloride, and water used in the regeneration of
ion exchange water softeners but also applied to the
mixed sodium, calcium and magnesium chloride waste
solution from regeneration.
Calcium (Ca) - One of the principal elements making up
the earth’s crust, the compounds of which when
dissolved, 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.
Calcium Hypochlorite (CaCl2O2) - A chemical
compound used as a bleach and a source of chlorine
water treatment; specifically useful because it is stable
as a dry powder and can be formed into tablets.
Capacity - An expression of the quantity of an
undesirable material which can be removed by a water
conditioner between servicing of the media (i.e. cleaning,
regeneration or replacement) as determined under
standard test conditions. For ion exchange water
softeners, the capacity is expressed in grains of
hardness removal between successive regenerations
and is related to the pounds of salt used in regeneration.
For filters, the capacity may be expressed in the length
of time or total gallons delivered between servicing.
Caustic Soda (NaOH) - The common name for sodium
Cation - An ion with a positive electrical charge, such as
calcium, magnesium and sodium.
Cation Exchange - Ion exchange process in which
cations in solution are exchanged for other cations from
an ion exchanger.
Cellulose Acetate (CA) and Cellulose Triacetate (CTA)
- A family of synthetic materials based on cellulose used
to make reverse osmosis membranes. While CTA is
superior to CA, under adverse water conditions both are
effective in removing a wide spectrum of impurities from
water. The disadvantage of cellulose-type membranes is
that they are subject to bacterial attack, particularly in
unchlorinated water supplies. CTA has superior bacterial
Channeling - The flow of water or other solution in a
limited number of passages in a filter or ion exchange
bed instead of distributed flow through all passages in
Chloramines - Chemical complexes formed from the
reaction between ammonia and chlorine. They are
presently being used to disinfect municipal water
supplies because, unlike chlorine, they do not combine
with organics in the water to form potentially dangerous
carcinogens such as trihalomethanes (THMs).
Chloramines can exist in three forms, the proportions of
which depend on the physical and chemical properties of
the water. Water containing chloramines may not be
used for fish or kidney dialysis equipment.
Chlorides (CI) - an ion which forms acids when
combined with hydrogen and salts when combined with
metal ions. Chlorides can be corrosive and impart a salty
taste to water.
Chlorine (CI2) - A gas widely used in the disinfection of
water and an oxidizing agent for organic matter, iron, etc.
Coagulant - A material, such as alum, which will form a
gelatinous precipitate in water and cause the
agglomeration of finely divided particles into larger
particles which can then be removed by settling and/or
Colloid - Very finely divided solid particles which will not
settle out of a solution; intermediate between a true
dissolved particle and a suspended solid which will settle
out of solution. The removal of colloidal particles usually
requires coagulation to form larger particles which may
be removed by sedimentation and/or filtration.
Compensated Hardness - A calculated value based on
the total hardness - the magnesium to calcium ratio and
the sodium concentration of a water. It is used to correct
for the reductions in hardness removal capacity caused
by these factors in cation exchange water softeners. No
single method of calculation has been widely accepted.
Conductivity - The quality or power to carry electrical
current. In water, the conductivity is related to the
concentration of ions capable of carrying electrical
Contact Time - The length of time water is in direct
contact with activated carbon (R.O.) or chlorine
(chlorination system.) This is a major factor in
determining how effectively impurities will be removed.
Corrosion - The destructive disintegration of a metal by
Cycle Time - The amount of time in seconds elapsed
between pump start and pump shut-down.
Dechlorination - The removal of excess chlorine
residual, often after super-chlorination.
Deionization (DI) - The removal of all ionized minerals
and salts (both organic and inorganic) from a solution by
a two-phase ion exchange procedure. First, positively
charged ions are exchanged for a chemically equivalent
amount of hydrogen ions. Second, negatively charged
ions are removed by an ion exchange resin for a
chemically equivalent amount of hydrogen ions. The
hydrogen and hydroxide ions introduced in this process
unite to form water molecules. The term is often used
interchangeably with demineralization.
Disinfection - A process in which pathogenic, disease
producing bacteria are killed. May involve disinfecting
agents such as chlorine or physical processes such as
Dissolved Solids - The weight of matter in true solution
in a stated volume of water. Includes both inorganic and
organic matter and is usually determined by weighing the
residue after evaporation of the water at 105°F or 180°C.
Distillation - The process in which a liquid, such as
water, is converted into its vapor state by heating and the
vapor cooled and condensed to the liquid state and
collected. Used to remove solids and other impurities
from water. Multiple distillations are required for extreme
DNA - Deoxyribonucleic acid constituting the genetic
material of the chromosome in a cell, responsible for
Drawdown - The amount of water delivered by the
storage tank between pump shut-down and pump start.
E-Coli (Escherichia Coli) - One of the members of the
coliform group of bacteria indicating fecal contamination.
Effluent - The stream emerging from a unit, system or
process such as the softened water from an ion
Exhaustion - The state of an ion exchange material in
which it is no longer capable of effective function due to
the depletion of the initial supply of exchangeable ions.
The exhaustion point may be defined in terms of a
limiting concentration of matter in the effluent or, in the
case of demineralization, in terms of electrical
Fecal - Matter containing or derived from animal or
Feed Pressure - The pressure at which water is
supplied to the R.O. module.
Feed Water - A term which refers to the water supply
that is put into a water treatment system for processing
(removal of impurities.)
Flocculation - The agglomeration of finely divided
suspended solids into larger, usually gelatinous,
particles. The development of a ‘floc’ after treatment with
a coagulant by gentle stirring or mixing.
Flow Control - A device designed to limit the flow of
water or regenerant to a predetermined value over a
broad range of inlet water pressures.
Flow Rate - The quantity of water or regenerant which
passes a given point in a specified unit of time, often
expressed in gallons per minute.
Flux - The flow rate of water through reverse osmosis
membranes, per square foot of surface.
Fouling - The process in which undesirable foreign
matter accumulates in a bed of filter media or ion
exchanger, clogging pores and coating surfaces and thus
inhibiting or retarding the proper operation of the bed.
Freeboard - The vertical distance between a bed of filter
media or ion exchange material and the overflow or
collector for backwash water. The height above the bed
of granular media available for bed expansion during
backwashing. May be expressed either as a linear
distance or a percentage of bed depth.
Grain (gr) - A unit of weight equal to 1/7000 of a pound
or 0.0648 gram.
Grain per Gallon (gpg) - A common basis for reporting
water analysis in the United States and Canada. One
grain per U.S. gallon equals 17.12 milligrams per liter
(mg/l) or parts per million (ppm). One grain per British
(Imperial) gallon equals 14.3 mg/l or ppm.
Greensand - A natural mineral, primarily composed of
complex silicates, which can be coated with manganese
oxide to form a catalytic absorptive surface. This surface
is used to attract ferrous iron and manganese as well as
to absorb dissolved oxygen which is used to oxidize iron,
manganese or hydrogen sulfide.
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 (gpg), parts per million (ppm) or
milligrams per liter (mg/l), all as calcium carbonate
Hard Water - Water with a total hardness of 1 gpg or
more as calcium carbonate equivalent.
Hydrologic Cycle - The natural 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
Hydrogen Sulfide (H2S) - A gas characterized by an
offensive odor, commonly referred to as “rotten egg”
odor. Flammable and poisonous in high concentrations,
corrosive to most metals and can even tarnish silver.
Detectable by most people in concentrations as low as
Hydrocharger - Trade name of a particular type of air
induction or injector valve.
Hydrolysis - The chemical degradation of an R.O.
membrane in water due to certain conditions such as
high pH. Cellulose based membranes are quite
susceptible to hydrolysis while the TFC type are virtually
Influent - The stream entering a unit, stream or process,
such as the hard water entering an ion exchange water
Ion - An atom, or group of atoms, which function as a
unit and have a positive or negative electrical charge due
to the gain or loss of one or more electrons.
Ion Exchange - A reversible process in which ions are
released from an insoluble permanent material in
exchange for other ions in a surrounding solution; the
direction of the exchange depends upon the affinities of
the ion exchanger for the ions present and the
concentrations of the ions in the solution.
Iron (Fe) - An element often found dissolved in ground
water (in the form of ferrous iron) in concentrations
usually ranging from 0-10 ppm (mg/l). It is objectionable
in water supplies because of the staining caused after
oxidation and precipitation (as ferric hydroxide); because
of the tastes; and because of unsightly colors produced
when iron reacts with tannins in beverages such as
coffee and tea.
Iron Bacteria - Organisms which are capable of utilizing
ferrous iron, either from the water or from steel pipe in
their metabolism and precipitating ferric hydroxide in their
sheaths and gelatinous deposits. These organisms tend
to collect in pipelines and tanks during periods of low
flow and to break loose in slugs of turbid water to create
staining, taste and odor problems.
Magnesium (Mg) - One of the elements making up the
earth’s crust, the compounds of which, when dissolved in
water, make the water hard. The presence of magnesium
in water is a factor contributing to the formation of scale
and insoluble soap curds.
Manganese (Mn) - An element sometimes found
dissolved in ground water, usually with dissolved iron but
in lower concentrations. Causes black stains and other
problems similar to iron.
Manganese Greensand - Greensand which has been
processed to incorporate in its pores and on its surface
the higher oxides of manganese. The product has a mild
oxidizing power and is often used in the oxidation and
precipitation of iron, manganese and/or hydrogen sulfide
and their removal from water.
Mechanical Filtration - The process of removing
suspended particles from water by a straining action. The
finest mechanical filters can remove bacteria as small as
Media - The selected materials in a filter that form the
barrier to the passage of certain suspended solids or
dissolved minerals. (Singular of media is medium).
Milligrams per Liter (mg/l) - A unit concentration of
matter used in reporting the results of water and
wastewater analysis. In dilute water solutions, it is
practically equal to parts per million but varies from the
ppm in concentrated solutions such as brine. As most
analysis are performed on measured volumes of water,
the mg/l is a more accurate expression of the
concentration and is the preferred unit of measure.
Micron - A linear measure equal to one millionth of a
meter or .00003937 inch. The symbol for the micron is
the Greek letter ‘ì’.
Micron Rating - The term applied to a filter or filter
medium to indicate the particle size above which all
suspended solids will be removed throughout the rated
capacity. As used in industry standards, this is an
“absolute” not “nominal” rating. (Refer to S-200,
Recommended Industry Standards for Household &
Commercial Water Filters.)
Mineral - A term applied to inorganic substances such as
rocks and similar matter found in the earth strata as
opposed to organic substances such as plant and animal
matter. Minerals normally have definite chemical
composition and crystal structure. The term is also
applied to matter derived from minerals such as the
inorganic ions found in water. The term has been
incorrectly applied to ion exchangers, even though most
of the modern materials are organic ion exchange resins.
Mineral Salts - The form in which minerals from
dissolved solids exist in water. Same as Total Dissolved
Solids. This is the so-called inorganic form of minerals. In
excess, they cause water to have a disagreeable taste.
Some are harmful to human health.
Molecular Weight - The sum of the atomic weights of
the individual atoms (from a periodic chart) that make up
a molecule of a particular substance (e.g. H2O1 H=1
atomic weight, 0=16 atomic weight, therefore, molecular
weight = 2 + 16 = 18.) Cellulose based membranes can
remove substances as light as MW of 300, while TFC
type membranes remove substances as light as MW of
Nanometer - A measure of a wavelength in the
electromagnetic spectrum. One nanometer equals 109
Neutralization - In general, the addition of either an acid
or a base to a solution as required to produce a neutral
solution. The use of alkaline or basic materials to
neutralize the acidity of some waters is common practice
in water conditioning.
Organic Iron - A ferrous iron molecule which is
enveloped in an organically complex molecule that
resists oxidation. May be present in water that contains a
great deal of colored colloidal turbidity.
Organics - Any of the compounds whose chemical
structure is based on carbon (e.g. carbon dioxide, wood,
sugar, protein, plastics, methane, THM, TCE, etc.)
Osmosis - A process of diffusion of a solvent, such as
water through a semipermeable membrane, which will
transmit the solvent but impede most dissolved
substances. The normal flow of solvent is from the dilute
solution to the concentrated solution. (See Reverse
Osmotic Pressure - The pressure created by the
tendency of water to flow in osmosis. Every 100 ppm of
TDS generates about 1 pound per square inch (psi) of
osmotic pressure. This osmotic pressure must first be
overcome by the water pressure for the reverse osmosis
membrane to be effective.
Oxidation - A chemical process in which electrons are
removed from an atom, ion or compound. The addition of
oxygen is a specific form of oxidation. Combustion is an
extremely rapid form of oxidation while the rusting of iron
is a slow form.
Oxidizing Agents - Any substance that oxidizes another
substance and is itself reduced in the process. Common
examples include: oxygen, chlorine, potassium
permanganate, hydrogen peroxide, iodine and ozone.
Ozone (O3) - An unstable form of oxygen occurring
naturally in the upper atmosphere or artificially produced
because of its strong oxidizing or disinfection
Particle Size - As used in industry standards, the size of
a particle suspended in water as determined by its
smallest dimension, usually expressed in microns.
Parts per Million (ppm) - A common basis for reporting
the results of water and waste water analysis, indicating
the number of parts by weight of water or other solvent.
In dilute water solutions, on part per million is practically
equal to one milligram per liter, which is the preferred
unit. 17.12 ppm equals one grain per U.S. gallon.
Pathogen - An organism which may cause disease.
PCB - Polychlorinated Biphenyls - A highly toxic
organic contaminant found in water supplies which is
suspected of causing cancer in humans.
pH - or the potential of hydrogen ion activity or
concentration. pH is a measure of the intensity of the
acidity or alkalinity of water on a scale from 0 to 14, with
7 being neutral. When acidity is increased, the hydrogen
ion concentration increases, resulting in a lower pH
value. Similarly, when alkalinity is increased, the
hydrogen ion concentration decreases, resulting in
higher pH. The pH value is an exponential function so
that pH is 10 times as alkaline as pH 9 and 100 times as
alkaline as pH 8. Similarly, a pH 4 is 100 times as acid
as pH 6 and 1000 times as acid as pH 7.
Potassium Chloride (KCI) - a compound consisting of
potassium and chloride, becoming increasingly popular
as a substitute for sodium chloride in regenerating water
Potassium Permanganate (KMnO4) - A powerful
oxidizing agent consisting of dark purple crystals with
blue metallic sheen. Explosive in contact with sulfuric
acid or hydrogen peroxide. Increases flammability of
combustible materials. Used to renew the black
manganese oxide coating on greensand media.
Precipitate - To cause a dissolved substance to form a
solid particle which can be removed by settling or filtering
such as in the removal of dissolved iron by oxidation,
precipitation and filtration. The term is also used to refer
to the solid formed and the condensation of water in the
atmosphere to form rain or snow.
Pre-treatment - Whatever alterations of the raw feed
water are required to prevent damage to the reverse
Product Water - The pure water that has been
separated from the feed water stream by the reverse
Pumping Rate - The amount of actual water that can be
drawn from a pressure system expressed in gallons per
minute (gpm) obtained by dividing the drawdown
(gallons) by the cycle time (seconds) and multiplying the
result by 60 (seconds.)
Quartz - A high grade of glass made using quartz sand.
Raw Water - Untreated water or any water before it
reaches a specific water treatment device or process.
Recovery - The amount of product water as compared
with the total amount of feed water. This will give a
measure of the efficiency of operation. For example,
starting with 10 gallons of feed water, if 6 gallons is
product water and 4 gallons reject water, the recovery is
Regenerant - A solution of a chemical used to restore
the capacity of an ion exchange or oxidation system.
Regeneration - In general, includes the backwash, brine
and fresh water rinse steps necessary to prepare a water
softener exchange bed for service after exhaustion.
Specifically, the term may be applied to the “brine” step
in which the sodium chloride solution is passed through
the exchanger bed. The term may also be used for
similar operations relating to demineralizers and certain
Rejection - The percentage of TDS removed from the
feed water. Typically greater than 90% rejection is
achieved with reverse osmosis.
Reject Water (same as Brine) - That portion of the feed
water that does not pass through the R.O. membrane
and which carries the remaining impurities to the drain.
Residual Chlorine - Chlorine remaining in a treated
water after a specified period of contact time to provide
protection throughout a distribution system. The
difference between the total chlorine added and that
consumed by oxidizable matter.
Resin - Synthetic organic ion exchange material such as
the high capacity cation exchange resin widely used in
Reverse Osmosis (R.O.) - A process that reverses, by
the application of pressure, the flow of water in the
natural process of osmosis so that the water passes from
the more concentrated to the more dilute solution
through a semi-permeable membrane.
Sediment - The sum of particles of dirt, clay, silt and
vegetation which float or are suspended in water and can
be removed by mechanical filtration. See Turbidity.
Semi-permeable - A term which applies to special
materials, both natural and synthetic, which allow certain
substances such as water to pass through (to permeate)
while blocking or rejecting the passage of other
substances such as dissolved solids and organics.
Service (Peak) Flow Rate - The greatest amount of
water (expressed in gallons per minute) that a particular
filter can effectively process based on short pump runs of
less than 10 to 15 minutes maximum.
Sequester - A chemical reaction in which certain ions
are bound into a stable, water soluble compound, thus
preventing undesirable action by the ions.
Soap - One of a class of chemical compounds which
possesses cleaning properties, formed by the reaction of
a fatty acid with a base of alkali. Sodium and potassium
soaps are soluble and useful but can be converted to
insoluble calcium and magnesium soaps (curd) by the
presence of these hardness ions in water.
Soda Ash (CNa2O3) - The common name for sodium
carbonate, a chemical compound used as an alkaline
builder in some soap and detergent formulations to
neutralize acid water and in the lime soda ash water
Total Hardness - The sum of all hardness constituents
in a water, expressed as their equivalent concentration of
calcium carbonate. Primarily due to 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 (see Hardness.)
Toxic - Having an adverse physiological effect on man.
Toxic Metals - Elemental metals that find their way into
water supplies from natural and industrial sources and
which are detrimental to human health (e.g. lead,
cadmium, mercury, arsenic.)
Toxic Organics - Carbon-based chemicals which are
frequently found in our water supplies and are harmful to
human health. They are usually from agricultural and
industrial effluents and hazardous waste dumps (e.g.
TCE, PCB, DCBP, pesticides, etc.)
Turbidity - Suspended biological, inorganic and organic
particles in water which may be in sufficient amount to
make the water seem cloudy (see Sediment.)
Virus - The smallest form of life known to be capable of
producing disease or infection, usually considered to be
of large molecular size. They multiply by assembly of
component fragments in living cells, rather than by cell
division as do most bacteria.
Volatile Organic Chemical (VOC) - Chemicals or
compounds with boiling points below 212°F, facilitating
their evaporation before water.
Water Softening - The removal of calcium and
magnesium, the ions which are the principal cause of
hardness, from water.