Glossary

absolute

Generally means 100% retention of particulates of the size equal to the filter rating.

absorption

To take up or drink in, as a sponge imbibes water.  The process of assimilation of molecules into the structure of a solid.  One substance taken into the body of another substance. 

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 and water. 

acidity

The quantitative capacity of a water or water solution to neutralize an alkali or base.  It is usually measured by titration with a standard solution of sodium hydroxide and expressed in terms of its calcium carbonate equivalent. 

activated carbon (AC)

Adsorptive particles or granules usually obtained by heating carbonaceous material in the absence of air or in steam and possessing a high capacity to selectively remove trace and soluble components from solution. 

activated carbon adsorption

Removal of soluble components from aqueous solution by contact with highly adsorptive granular or powdered carbon.

activated carbon treatment

Treatment process in which water is brought into contact with highly adsorptive granular or powdered carbon to remove soluble components.  Process may be applied to raw water, primary effluent, or chemically clarified wastewater for nonspecific removal of organics, or to secondary effluent as a polishing process to remove specific organics. 

activated silica

A material usually formed from the reaction of a dilute silicate solution with a dilute acid and used as a coagulant aid. 

adsorbent

A material, usually solid, capable of holding gases, liquids, and/or suspended matter at its surface and in exposed pores.  Activated carbon is a common adsorbent used in water treatment. 

adsorption

The process in which matter adheres to the surface of an 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 the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water. 

agglomeration

The coalescence of dispersed suspended matter into larger flocs or particles which settle rapidly. 

air gap

A clear, vertical space between a water or drain line and the flood level of a receptacle used to prevent backflow or siphonage from the receptacle in the event of a negative pressure or vacuum.  Most plumbing codes require the air gap to be a least twice the diameter of the water or drain line with a minimum of 1 ½ inches. 

air stripping

A technique for removal of volatile substances from a solution.  Employs the principles of Henry’s Law to transfer volatile pollutants from a solution of high concentration into an air stream of lower concentration.  The process ordinarily is designed so that the solution containing the volatile pollutant contacts large volumes of air. 

algae

Small primitive plants containing chlorophyll commonly found in surface water.  Excessive growths may create taste and odor problems and consume dissolved oxygen during decay. 

alkali

A group of water soluble mineral compounds usually considered to have moderate strengths as bases as opposed to the caustic or strongly basic hydroxides, although this differentiation is not always made.  In general, the term is applied to the carbonates, borates, phosphates, and silicates when these are present in the water or solution.

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. 

alum

A common name for aluminum sulfate (Al2(SO4)3, used as a coagulant. 

amoeba

A small, single-celled animal or protozoan.

anion

A negatively charged ion in solution such as bicarbonate, chloride, or sulfate.

anode

The positive pole of an electrolytic system; the metal which goes into solution in a galvanic cell.  Anodes of metals such as magnesium or zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.

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 similar 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 are subject to attrition during backwashing, regeneration, and service. 

backflow

Flow of water in a pipe or line in a direction opposite to normal flow; often associated with back siphonage or the flow of possibly contaminated water into a potable water system. 

backflow preventer

A device or system installed in a water line to stop backflow from a nonpotable source. 

backwash

The process in which beds of filter or ion exchange media are subjected to flow opposite to the service flow direction; to loosen the bed and to flush suspended matter (collected during the service run) to waste. 

bacteria

Unicellular microorganisms which typically reproduce by cell division.  Although usually classed as plants, bacteria contain no chlorophyll. 

base

A substance which releases hydroxyl ions when dissolved in water.  Bases react with acids to form a neutral salt and water. 

bed

The filter media or ion exchange resin in a column or other tank or operational vessel. 

bed depth

The height of the filter media or ion exchanger in the vessel after preparation for service expressed in inches or centimeters. 

bed expansion

The increase in volume of a bed of the ion filter or exchanger media during backwashing due to lifting and separation of the bed material.  Usually expressed as the percent of increase of bed depth. 

bicarbonate alkalinity

The alkalinity (HCO3) of a water due to the presence of bicarbonate ions. 

bleach

An oxidizing agent formulated to break down colored matter; includes the widely used hypochlorites, as well as perborates and other special purpose materials. 

breakthrough

The appearance in the effluent from a water conditioner of the material to be removed by the conditioner, such as hardness in the effluent of a softener, or turbidity in the effluent of a mechanical filter.  An indication that regeneration, backwashing, or other treatment is necessary for further service. 

buffer

A chemical which causes a solution to resist changes in pH, or to shift the pH to a specific value. 

buffer action

The action of certain ions in solution in opposing a change in hydrogen-ion concentration. 

buffer solution

A solution containing two or more substances which, in combination, resist any marked change in pH following addition of moderate amounts of either strong acid or base. 

bypass

A connection or a valve system that allows untreated water to flow to a water system while a water treatment unit is being regenerated, backwashed, or serviced; also applied to a special water line installed to provide untreated water to a particular tap, such as a sill cock. 

calcium

One of the principal elements (Ca) 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 carbonate equivalent

A common basis for expressing the concentration of hardness and other salts in chemically equivalent terms to simplify certain calculations; signifies that the concentration of a dissolved mineral is chemically equivalent to the stated concentration of calcium carbonate. 

calcium hypochlorite

A chemical compound, [Ca (CLO)24H2O], used as a bleach and a source of chlorine in 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. 

carbon dioxide

A gas (CO2) present in the atmosphere and formed by the decay of organic matter; the gas in carbonated beverages; in water, it forms carbonic acid. 

carbonate

The CO3 ion.

carbonate alkalinity

Alkalinity (CO3) due to the presence of the carbonate ion. 

carbonate hardness

Hardness due to the presence of calcium and magnesium bicarbonates and carbonates in water; the smaller of the total hardness and the total alkalinity. 

carcinogen

A material substance that induces excessive or abnormal cellular growth cancer in an organism. 

cartridge

Any removable, preformed, or prepackaged component containing a filtering media or ion exchanger.  Also referred to as “element”.

catalyst

A substance that increases the rate or yield of a chemical reaction without being consumed itself.

catalyzed oxidation

Enhancement of chemical or biological oxidation by the addition of catalytic agents that promote higher rates of reaction. 

cathode

The negative pole of an electrolytic system; an electrode where reduction occurs.

cathodic protection

A corrosion control system in which the metal to be protected is made to serve as a cathode either by the deliberate establishment of a galvanic cell or by impressed current. 

cation

An ion with a positive electrical charge, such as calcium, magnesium, sodium, iron, lead, and manganese. 

cation exchange

Ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger. 

cationic flocculant

A polyelectrolyte with a net positive electrical charge. 

caustic

Any substance capable of burning or destroying animal flesh or tissue.  The term is usually applied to strong bases such as lye. 

caustic soda

The common name for sodium hydroxide, (NaOH).

channeling

The flow of water or other solution in a limited number of passages in a filter or ion exchanger bed instead of distributed flow through all passages in the bed.  May be due to fouling of the bed and plugging of many passages, poor distributor design, flow rates which are too low, faulty operational procedures, or other causes. 

chelate

To form a complex chemical compound in which an ion, usually metallic, is bound into a stable ring structure. 

chelating agent

A chemical compound sometimes fed to water to tie up undesirable metal ions, keep them in solution, and eliminate or reduce the normal effects of the ion. 

chemical feeder

A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow. 

chloramine

A combination of chlorine and a small amount of ammonia, chloramine is a disinfectant used by some water utilities. The addition of the ammonia helps to make the solution more stable and longer lasting. Chloramines can cause an adverse effect on the taste and odor of water.

chlorinator

A mechanical device specifically designed to feed chlorine gas or solutions of its compounds, such as hypochlorites, into a water supply in proportion to the flow of water. 

chlorine

A gas used by many water utilities for the disinfection of water and as an oxidizing agent for organic matter and some metals. It imparts a noticeable taste and odor to water, and may contribute to the formation of trihalomethanes (THM).

chlorine demand

A measure of the amount of chlorine which will be consumed by organic matter and other oxidizable  substances in a water before a chlorine residual will be found; the difference between the total chlorine fed and the chlorine residual. 

clarification

The removal of small quantities (<2%) of fine particulate matter (solids) from a liquid (water) to improve the product liquid.  Generally, clarifiers will remove particles from 2 to 100 micrometers in size.  Clarification methods include filtration, gravity and centrifugal sedimentation, and magnetic separation. 

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 filtration.

coagulant aid

A material which is not a coagulant but which improves the effectiveness of a coagulant often by forming larger or heavier particles, speeding the reactions, or by permitting reduced coagulant dosage. 

coagulation

The process in which very small, finely divided solid particles, often colloidal in nature, are agglomerated into larger particles.

co-current flow

(See downflow.)

collector

A device or system designed to collect backwash water from a filter or ion exchange bed.  May also be used as an upper distributor to spread the flow of water in downflow column operation. 

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.

color

The shade or tint imparted to water by substances in true solution, and thus not removed by mechanical filtration; most commonly caused by dissolved mineral matter.

color throw

The discharge of color to the effluent of a filter or ion exchange system by any component.  It usually occurs after a period of standing which allows slowly soluble colored matter to accumulate in the system. 

column operation

The process in which the solution to be treated is passed through a vessel containing a bed of filter media or ion exchange; may be either upflow or downflow. 

combined available chlorine

The chlorine present as chloramines or other derivatives in a water, but still available for disinfection and the oxidation of organic matter.  The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in action. 

composite sample

A mixture of a number of single or “grab” samples intended to produce a typical or average sample when wide variations in quality or characteristics may occur; may be made up of equal volumes of individual samples or of single samples proportioned to variations in flow or usage. 

contamination

The addition of foreign matter to a substance which reduces the value of the substance or interferes with its intended use.

convection

In physics, mass motions within a fluid resulting in transport and mixing of the properties of that fluid caused by the force of gravity and by differences in density due to nonuniform temperature. 

corrosion

The destructive disintegration of a metal by electrochemical means.

countercurrent flow

(See upflow)

cross connection

A direct link between a potable water system and a non potable water system which would permit undesirable substances to be drawn into the potable water.

cross-sectional area

The area of a plane at a right angle to the direction of flow through a tank or vessel; often expressed in square feet and related to the flow rate (Example: 5 gallons per minute per square foot of ion exchanger bed area).

cube

A slang expression sometimes used to mean a cubic foot of ion exchanger or filter media.

cubic foot

The common basis for the measurement of the volume of ion exchangers or loose filter media.  The measurement is made after a specific process including backwashing and settling of the bed and draining excess water from above the bed.  A cubic foot equals 28.3 liters.

cycle

A series of events or steps which ultimately lead back to the starting point, such as the exhaustion regeneration cycle of an ion exchange system; sometimes incorrectly used in reference to a single step of a complete cycle.

cyst

(See spore.)

dechlorination

The removal of excess chlorine residual, often after super-chlorination.  (See super-chlorination.)

deionization

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 removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen icons.  Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions.  The hydrogen and hydroxide ions introduced in this process unite to form water molecules.  The term is often used interchangeably with demineralization. 

demineralization

The removal of ionized inorganic minerals and salts (not organic materials) from a solution by a two-phase ion exchange procedure; similar to deionization, and the two terms are often used interchangeably. 

density

The mass of a substance per specified unit of volume; for example, pounds per cubic foot.  True density is the mass per unit volume excluding pores; apparent density is the mass per unit volume including pores.

diaphragm pump

A form of positive displacement pump in which the reciprocating piston is separated from the solution by a flexible diaphragm, thus protecting the piston from corrosion and erosion and avoiding problems with packing and seals. 

diatomaceous earth, diatomite

A processed, natural material, chiefly the skeletons of diatoms, used as a filter medium. 

differential pressure

The difference in pressures at two points in a water system; may be due to differences in elevation or to friction losses or pressure drops due to resistance to flow in pipes, softeners, filters or other devices.

diffusion

The process whereby particles of liquids intermingle as the result of their spontaneous movement in dissolved substances moving from a region of high concentrations to one of low concentration.

disinfection

A process in which pathogenic (disease producing) bacteria are killed; may involve disinfecting agents such as chlorine or physical processes such as heating.

dissociation

The separation of molecules into positively and negatively charged ions in water solution.

dissolved solids

The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105 or 180° C. 

distributor

(See collector.)

dolomite

A specific form of limestone (CaMg (CO3)) 2 containing chemically equivalent concentrations of calcium and magnesium carbonates; the term is sometimes applied to limestone with compositions similar to true dolomite.

domestic

A slang term sometimes applied to water conditioning equipment designed for residential use.

downflow

A term applied to designate the direction (down) in which water or a regenerant flows through an ion exchanger or filter during any phase of the operating cycle.  Also referred to as co-current flow.

dynamic

Active, alive, or tending to produce motion as opposed to static, resting, or fixed. 

dynamic system

A system or process in which motion occurs, or includes active forces, as opposed to static conditions with no motion. 

eddy

A circular movement whirlpool occurring in flowing water caused by currents set up in the water by obstructions. 

eductor

A device utilizing a nozzle and throat and installed in a stream of water to create a partial vacuum to draw air or liquid into the stream.  Commonly used to draw brine into a water line for the regeneration of an ion exchange water softener.

effective size

A measure of the size of particles of ion exchanger or filter media, defined as the diameter of a specific particle in a bed, batch, or lot which has 10 percent smaller and 90 percent larger particles.

effluent

The stream emerging from a system or process such as the softened water from an ion exchange softener.  The filtrate water from a filter.

ejector

(See eductor.)

electron

A fundamental particle found in the atom and which carries a single negative charge.  In a neutral atom, the positive charges of the nucleus are balanced by an equal number of negative electrons in the field surrounding the nucleus.  Ions are formed when atoms gain or lose electrons, thus achieving positive or negative net charges. 

element

The disposable filtering cartridge itself in a replaceable cartridge-type filter.

endpoint

The point at which a process is stopped because a predetermined value of a measurable variable is reached; the endpoint of an ion exchanger water softener service run is the point at which the hardness of the softener effluent increases to a predefined concentration, often 1.0 grain per gallon; the endpoint of a filter service run may be the point at which the pressure drop across the filter reaches a predetermined value; the endpoint of a titration is the point at which the titrant produces a predetermined color change, pH value, or other measurable characteristic.

epm

The abbreviation for “equivalent per million.”

equilibrium

The state in which the action of multiple forces produces a steady balance or seeming lack of change; may be due to a true stop in action or due to continuing actions which neutralize each other resulting in no net change.

equilibrium reaction

A chemical reaction which proceeds primarily in one direction until the concentrations of reactants and products reach an equilibrium which usually can be expressed as ratio or other mathematical relationship.

equivalent per million

A unit of concentration used in chemical calculations, calculated by dividing the concentration in ppm or mg/L by the equivalent weight.

equivalent weight

The weight in grams of an element, compound, or ion which would react with or replace 1 gram of hydrogen; the molecular weight in grams divided by the valence.

filter

Specifically, a device or system for the removal of solid particles (suspended solids); in general, includes mechanical, adsorptive, oxidizing and neutralizing filters. (Nonhealth related.)

filter area

The effective area through which water approaches the filter media often expressed in square feet.  Also referred to as surface area.

filter media

(See media.)

filter rating

(See micron rating.)

filtrate

The effluent liquid which has passed through any style filter.

fines

Extremely small particles of filter media or ion exchange material formed either in the manufacturing process or as a result of breakdown; undesirable in most systems because of high pressure drop.

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.

fluoridation

The addition of a fluoride compound to a potable water supply to produce the concentration desired for the reduction in incidence of dental caries.

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. 

free available chlorine

The concentration of residual chlorine present as dissolved gas, hypochlorous acid, or hypochlorite not combined with ammonia or in other less readily available form. 

free carbon dioxide

Carbon dioxide (CO2) present in water as the gas or as carbonic acid, but not that combined in carbonates or bicarbonates.

free chlorine

(See free available chlorine.)

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 was a linear distance or a percentage of bed depth.

gallon

A common unit of liquid volume; the U.S. gallon has a volume of 231 cubic inches or 3.78533 liters; the British (Imperial) gallon has a volume of 277.418 cubic inches or 4.54596 liters.

grab sample

A single sample of material collected at one place and one time; represents only the specific material at the time and place of sampling.

greensand

A natural mineral, primarily composed of complex silicates, which possess ion exchange properties. 

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.

head

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.

hydration

The chemical combination of water into a substance.

hydraulic

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.

hydroxide

A chemical compound of an element or elements with the hydroxyl (OH) anion.

hydroxyl

The “OH” anion which has a single negative charge and provides the characteristics common to bases.

hypochlorite

Calcium and sodium hypochlorites (CLO2) are commonly used as bleaches and as disinfecting agents.

indicator

A material which can be used to show the endpoint of a chemical reaction, usually by a color change, or a chemical concentration by a depth or shade of color.

influent

The stream entering a unit or process, such as the hard water entering an ion exchange water softener, or turbid water entering a filter system.

inorganic matter

Substances not derived from living organisms and containing no organically produced carbon; includes rocks, minerals, and metals.

installation

The process of connecting conditioning equipment into the water system and a drain line provided where necessary.  The term is also used to refer to the complete assembly of piping, valves, drain line, water conditioning unit, and related equipment.

intermittent flow

The term usually applied to the interrupted patterns of water usage; also used in reference to specific on-off flow patterns selected to test the performance of water conditioning equipment under standard conditions which may or may not be similar to actual patterns of use. 

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.

ionization

The process in which atoms gain or lose electrons and thus become ions with positive or negative charges; sometimes used synonymously with dissociation; the separation of molecules into charged ions in solution. 

iron

An element (Fe) often found dissolved in ground water (in the form of ferrous iron) in concentrations usually ranging from zero to 10 ppm (mg/L).  It is objectionable in water supplies because of the staining caused after oxidation and precipitation (as ferric hydroxide), because of 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 pipe lines and tanks during periods of low flow and to break loose in slugs of turbid water to create staining, taste, and odor problems.

There are currently no glossary terms for this letter

kilo

A prefix used to indicate 1000 of the succeeding unit.  (Is also sometimes used as an abbreviation for kilogram.)

kilograin (Kgr.)

One thousand grains.

kilogram (Kg.)

One thousand grams.

laminar flow

The form of flow of a fluid in which the flow paths are in smooth, parallel lines with essentially no mixing and no turbulence.

lime

The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide, Ca(OH)2.

lime scale

Hard water scale containing a high percentage of calcium carbonate.

limestone

A sedimentary rock, largely calcium carbonate (CaCO3), usually containing significant amounts of magnesium carbonate.  The calcite grade is used in filtration and for pH modification.

magnesium

One of the elements (Mg) 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

An element (Mn) sometimes found dissolved in groundwater, 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 it pores and on its surface the higher oxides of manganese.  The product has mild oxidizing power and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water. 

manganese zeolite

Synthetic gel zeolite which has been processed in the same manner as manganese greensand and used for similar purposes.

mechanical filter

A filter primarily designed for the removal of suspended solid particles as opposed to filters with additional capabilities.

media

The selected materials in a filter that form the barrier to the passage of certain suspended solids or dissolved molecules.

medium

Singular form of media.

mg/L

The abbreviation of milligrams per liter.

microfiltration (MF)

The separation or removal of particulates of more than 0.02 μm or less than 10.0 μm size from liquids.

micron

A linear measure equal to one millionth of a meter, or .00003937 inch.  The symbol for the micron is the Greek letter “μ.”

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.

mil

One thousandth of an inch.

milli-

The prefix used with units of measure to indicate one thousandth of the unit.  Example: a milliliter is one thousandth of a liter.

milligram per liter (mg/L)

A unit concentration of matter used in reporting the results of water and wastewater analyses.  In dilute water solutions, it is practically equal to the part per million, but varies from the ppm is concentrated solutions such as brine.  As most analyses 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. 

millimicron

A unit of length equal to one thousandth of a micron often used to express the wavelength of colors of visible light in colorimetric analytical procedures.  The symbol for the millimicron is “mμ.”

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 acidity

Acidity due to the presence of inorganic acid such as hydrochloric, sulfuric, and nitric acid, as opposed to acidity due to carbonic acid or organic acids. 

mole

The molecular weight of a chemical compound expressed in grams.

molecule

The simplest combination of atoms that will form a specific chemical compound; the smallest particle of a substance which will still retain the essential composition and properties of that substance and which can be broken down only into atoms and simpler substances.

most probable number (MPN)

The term used to indicate the number of organisms which, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests; usually expressed as a number per 100 ml of water.