M alkalinity

SEE alkalinity tests.

Macroporous Resin

A special grade of ion exchange resins which have large pores and a higher resistance to oxidation and organic fouling. They were developed to provide increased surface area for reactions with organic matter with large molecular weights. Macroporous resins are manufactured with a third ingredient that is soluble in the styrene and divinylbenzene monomers but becomes insoluble in the polymer structure as it is formed. The third ingredient is then removed from the resin structure by a solvent leaving a resin bead that has both a continuous resin phase and a continuous pore phase, resulting in considerable net porosity and internal surface area. Macroporous resins, which are produced in both anion and cation versions, contain higher levels (12% or more) of divinylbenzene cross-linking, which reduces the swelling of the polymer resin in water. Also called macroreticular resin.

Macrorecticular resin

SEE macroporous resin.

Macroscopic Organisms

Organisms big enough to be seen by the eye without the aid of a microscope.

Macroscopic Organisms

Organisms big enough to be seen by the eye without the aid of a microscope.


Magnesium oxide (MgO) that has been specially processed.  Magnesia water treatment can be used for pH modification of water.

Magnesium (Mg)

One of the elements that make up the earth's crust as part of many rock-forming minerals such as dolomite.     Magnesium and calcium dissolved in water constitute hardness. The presence of magnesium in water contributes to the formation of scale and the insoluble soap curds which identify hard water.


(Fe3O4) A black magnetic oxide of iron that is extremely dense and used as a coagulant and filter medium in water treatment. Magnetite is readily recognized by its strong attraction to magnets. Also called lodestone.

Makeup Water

Treated water added to the water loop of a boiler circuit or cooling tower to make up for the water lost by steam leaks or evaporation.


Very dangerous or virulent, causing or likely to cause death.

Managerial Controls

Methods of nonpoint source pollution control that are derived from managerial decisions, such as changes in application times or rates for agrochemicals.

Manganese (Mn)

An element sometimes found dissolved in groundwater, usually in combination with - but in lower concentrations than- iron. Manganese is noticeable because in concentrations above 0.05 mg/L it causes black staining of laundry and plumbing fixtures. Important ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite.

Manganese Dioxide

(MnO2) A dark brown or gray-black insoluble compound found in nature as pyrolusite, made synthetically, and used as an oxidizing agent in water treatment and as a starting material for permanganate compounds such as potassium permanganate.

Manganese Dioxide-Coated Pumicite

An oxidizing catalyst medium used to remove iron and manganese. The manganese is sacrificial.

Manganese Greensand

Greensand which has been processed to incorporate the higher oxides of manganese into its pores and onto its surface. Manganese greensand has a mild oxidizing power and is often used in the oxidation, precipitation, and removal of iron, manganese, and/or hydrogen sulfide. It is regenerated by solutions of potassium permanganate (KMnO4).

Manganese Zeolite

A synthetic gel zeolite (sodium alumino silicate) which has been converted to the manganese form by the same process as manganese greensand and is used for the same treatment applications as manganese greensand.     Manganese zeolite is also regenerated with potassium permanganate (KMnO4).

Manganite [MnO(OH)]

A form of manganese ore, consisting of manganic hydroxide, which is used in filters designed to reduce iron, manganese, and/or hydrogen sulfide and requires a very high backwash rate because of its very high density (specific gravity 4.3). Similar to pyrolusite.


A large pipe to which a series of smaller pipes are connected. Also called a header.

Man-made beta particle and photon emitters

All radionuclides emitting beta particles and/or photons listed in Maximum Permissible Body Burdens and Maximum Permissible Concentration of Radionuclides in Air or Water for Occupation Exposure, NBS Handbook 69, except the daughter products of thorium-232, uranium-235, and uranium-238.


An instrument for measuring pressure. Usually, a manometer is a glass tube filled with a liquid that is used to measure the difference in pressure across a flow-measuring device such as an orifice or Venturi meter.     The instrument used to measure blood pressure is a type of manometer.

Margin of Safety (MOS)

Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population.

Marine Salt

An early chemical name for salt, partly because of its source.

Mass Spectrometry (MS)

A method of chemical analysis, used as a detector in gas chromatography, for example, in which the compounds emerging from the chromatograph are fragmented and ionized by bombardment with a beam of electrons. An electromagnetic field separates the ions according to their individual mass-to-charge ratios into a characteristic mass spectrum of the molecule. A computer analyzes the spectra and makes it possible to identify molecules even in cases of poor separation on the chromatography column, hence the advantage of mass spectrometry compared to selective chromatograph detectors.

Mass Transfer

The movement of molecules of a substance to and across an interface from one phase to another. For example, the amount (mass) of ozone that transfers from air, across the air-water interface and into water; or the amount of organic material that transfers from water to a solid adsorption surface. The rate and amount of mass transfer can be increased by: 1. enlarging the interface boundary by increasing the area of the interface or by rapid renewal or clearance of the interface;  2. increasing the concentration difference (which is the driving force) across the interface boundary, and/or;   3. increasing the length of time (contact time) the interface boundary exists.

Mass Transfer Zone

The region in a treatment unit where the concentration of the contaminant(s) of interest in the water or fluid decreases from influent concentration(s) to the lowest detectable concentration(s).  For example, the region of an adsorption column in which adsorption is taking place.

Mathematical Model

Model used during risk assessment to perform extrapolations.

Maximum contaminant level (MCL)

SEE drinking water standards

Maximum contaminant level goals (MCLGs)

SEE drinking water standards

Maximum Total Trihalomethane Potential (MTTP)

The maximum concentration of total trihalomethanes produced in a given water containing a disinfectant residual, after seven days at 25 degrees C or above.

MBAS Methylene-Blue- Active Substances

These substances are used in surfactants or detergents.


Maximum Contaminant Level.


Maximum Contaminant Level Goal.

Mean Particle Diameter

The weighted average particle size, in millimeters, of the media particles or beads in a filter or ion exchange bed.  Mean particle diameter is computed by multiplying the percent retained in a size fraction by the respective mean sieve openings, summing these values and dividing by 100.

Measured Variable

A characteristic or component part that is sensed and quantified (reduced to a reading of some kind) by a primary element or sensor.

Mechanical Claim

A manufacturer’s claim that is based on reduction in concentration of an unwanted contaminant by a physical means. An example would include size exclusion.

Mechanical Filter

SEE barrier filter.

Mechanical Joint

A flexible device that joins pipes or fittings together by the use of lugs and bolts.


A selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules which are suspended or dissolved in water. It is also common to use the term media to refer to ion exchange resin products.  Media is the plural form of medium and refers to more than one type of barrier material.


A statistical term representing the middle value of a series of numbers when the numbers are arranged in order of their numerical quantity or value.  Equal numbers of data points can be found that are greater than or less than the median.  For example, in the sequence 1,3,4,7,8,10,12, the median is 7.


The singular form of media.

Medium Size Public Water System

A public water system that serves greater than 3,300 and less than or equal to 50,000 persons.


Abbreviation for megohm. Meg means one million.


1. A prefix meaning large; 2. A million of; or multiplied by one million.    


A unit of electrical resistance equal to one million ohms.

Membrane, ion exchange

SEE ion exchange membrane


A thin sheet or surface film, either natural or man-made, of microporous structure that performs as an efficient filter of particles down to the size range of chemical molecules and ions. Such membranes are termed "semipermeable" because some substances will pass through, but others will not. Usually small ions, water, solvents, gases, and other very small molecules can pass through a membrane, but other ions and macromolecules such as proteins and colloids are barred from passage.  Man-made (synthetic) membranes are highly engineered polymer films about 100 angstroms thick and with controlled distributions of pores ranging from 5 to 5,000 angstroms in diameter. Membranes are used in reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and as pleated final filter cartridges in water treatment. SEE ALSO cellulose acetate (CA); cellulose triacetate (CTA); charged polysulfone membrane.

Membrane Filtration

A laboratory analytical technique for the quantitative and qualitative analysis of bacterial or particulate matter in a water sample. Upon filtering through a membrane of specified pore size (e.g. 0.45 micron), bacteria and particles of larger size are separated from the water sample and are retained on the filter. Then by incubation with a suitable nutrient and temperature, the captured bacteria will grow to visible colonies that can be counted; or by careful weighing, the amount of suspended particulate solids can be determined in the water sample.

Membrane softening

SEE nanofiltration


The curved top of a column of liquid (water, oil, mercury) in a small tube. When the liquid wets the sides of the container (as with water), the curve forms a valley. When the confining sides are not wetted (as with mercury), the curve forms a hill or upward bulge.

Mercury vapor ultraviolet light

The ultraviolet light given off as the result of an electron flow through an ionized mercury vapor between electrodes in an ultraviolet lamp. The mercury vapor UV wavelength, which is most destructive to microorganisms in water, is 254 nanometers.

Mesh Size

Mesh is the number of openings in a square inch of a screen or sieve.  It is equal to the square of the number of strands of metal or plastic screening per lineal inch. Ion exchange and filter media are graded by U.S. mesh or screen sizes according to the percent of the medium's particles that will pass through or be retained on certain mesh screens. Standard U.S. mesh screen #16 equates to a 1.19 millimeter particle diameter; mesh size #40 is 0.42 millimeters. Therefore, media rated as 95 percent -16+40 U.S. mesh would have 95 percent or more of the media particles with sizes between 0.42 and 1.19 mm in diameter.


Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.


The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).


Any product of metabolism, especially a transformed chemical.


The middle layer in a thermally stratified lake or reservoir. In this layer, there is a rapid decrease in temperatures with depth. Also called the thermocline.


Pertaining to the transfer of disease from one organ or part to another not directly connected with it.


A colorless, odorless, flammable gas consisting of the hydrocarbon (CH4) and resulting from the decay of vegetable matter or manure due to the action of anaerobic bacteria in swampy land, closed landfills, or sewage disposal plants. Methane is also known as biogas and it is called swamp gas when produced in marshy land. Coal miners know methane as one of the main components of fire-damp and also of coal-gas.     Methane dissolved in water gives the water a milky cast, and since it is flammable, methane must be safely aerated and vented to the atmosphere during removal.


A serious condition, found mostly in young infants under six months of age (or newborn animals), in which the oxygen-carrying capacity of the blood is reduced as a result of a reaction with nitrite (NO2-), which changes the healthy hemoglobin to an inactive methemoglobin form. As a result of the higher pH conditions in the gastrointestinal tract of infants and newborn animals, nitrate (NO3-), which is consumed in food or water, can be transformed into nitrite more readily than would occur with adults.


A pesticide which causes adverse health effects in domestic water supplies and is also toxic to freshwater and marine aquatic life. The chemical name for methoxychlor is 2,2-bis (p-methoxyphenol)-1,1,1-trichloroethane.

Methyl Orange

An acid-base indicator that turns red in a solution below three on the pH scale and yellow between pH of 4.4 and 7.0.

Methyl Orange Alkalinity

A measure of the total alkalinity in a water sample.     The alkalinity is measured by the amount of standard sulfuric acid required to lower the pH of the water to a pH level of 4.5, as indicated by the change in color of methyl orange from orange to pink.     Methyl orange alkalinity is expressed as milligrams per liter equivalent calcium carbonate.

Methyl Tertiary Butyl Ether (MTBE)

Since MTBE was incorporated in the mid-1980s into gasoline mixtures as an antiknock replacement for aromatics and as an "oxygenator" to reduce carbon monoxide emissions, it has increasingly appeared in groundwater due to spills of reformulated gasoline and leaking underground storage tanks at gasoline stations.  It is highly water soluble and its appearance typically marks the leading front of a contamination plume.  The molecular weight of MTBE (C5H12O) is 88.15.    In terms of noncarcinogenic effects, it has low oral toxicity, but at the gasoline pump and in the automobile, symptoms such as airway and eye irritation have been reported.  In water, MTBE has a noticeable odor at 20 to 40 µg/L (U.S. Environmental Protection Agency, 1997).  Though MTBE is not mutagenic/genotoxic, exposure to high levels by inhalation (8000 ppm) or by ingestion (1000 mg/kg) was associated with the development of lymphoma and leukemia, as well as liver, renal, and testicular cancers in rodents (Burleigh-Flayer et al., 1992; Belpoggi et al., 1995).    The relevance of these cancers to human health is not clear, but "weight of evidence suggests that MTBE is an animal carcinogen."  "Concentrations in the range of 20 to 40 µg/L are about 20,000 to 100,000 (or more) times lower than the range of exposure levels in which cancer or non-cancer effects were observed in rodent tests." (U.S. Environmental Protection Agency, 1997). Thus, the USEPA says "protection of the water source from unpleasant taste and odor will also protect consumers from potential (MTBE) health effects."    MTBE is adsorbed onto activated carbon similar to chloroform, but with a use rate of 2-3 times that of chloroform, i.e., the life of the activated carbon may be only 1/2 to 1/3 of that for chloroform when MTBE will begin to break through.  For concentrations of MTBE greater than 100 µg/L or parts per billion, pretreatment with an atmospheric air stripping system with repressurization is recommended prior to activated carbon adsorption.

Methylene-Blue Active Substances (MBAS)

These substances are used in surfactants or detergents.


Milligrams per liter.


(Backward spelling of ohm) A unit of conductance equal to the reciprocal of the ohm. Also called siemens.

Microbial Growth

The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton, and fungi.


Similar to biocide but does not necessarily kill macroscopic and multicelled organisms.

Microbiologically unsafe water

Water that (1) is known to contain disease-causing bacteria, viruses, protozoa or other disease-causing microbiological agents, or (2) shows a positive test for an indicator organism such as coliform, fecal coliform, or E. coli bacteria, or (3) is determined unsafe by an appropriate health or regulatory agency.


The separation or removal from a liquid of particulates and microorganisms in the size range of 0.1 to 2 microns in diameter.


One-millionth of a gram 

(3.5 X 10-8 oz = 0.000000035 oz.).

Micrograms Per Liter

One microgram of a substance dissolved in each liter of water. This unit is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.


One millionth of an ohm. The unit of measurement for testing the electrical resistance of water to determine its purity. The closer water comes to absolute purity, the greater its resistance to conducting an electric current.     Absolutely pure water has a specific resistance over 18 million ohms across one centimeter at a temperature of 78 degrees F (25 degrees C).


A metric unit of length equal to one millionth of a meter or one thousandth of a millimeter or about 0.00003937 inches. Also called a micrometer, µm.

Micron Rating

A measurement applied to filters or filter media to indicate the particle size at which suspended solids above that size will be removed. As used in the water treatment industry standards, this may be an absolute rating or a nominal rating.


A living organism invisible or barely visible to the naked eye and generally observable only through a microscope. Also called a microbe. Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses. Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses.

Microporous Resin

Ion exchange resin with low porosity, usually polystyrene cross-linked typically with about three percent divinylbenzene. The lower cross-linking means microporous resins also have less strength and less resistance to degradation, swelling, and mushing.


One-millionth of a siemens (formerly called mho). The microsiemens is the practical unit of measurement for conductivity and is used to approximate the total dissolved solids content of water. Water with 100 mg/L (ppm) of sodium chloride will have a specific resistance of 4,716 ohms-centimeter and a conductance of 212 microsiemens per centimeter. Absolute pure water, from a mineral content standpoint, has a conductivity of 0.03 microsiemens per centimeter at 25 degrees C (78 degrees F). Also called micromhos.


One millionth of a watt.

Microwatt-Seconds Per Square Centimeter

A unit of measurement of intensity and retention or contact time in the operation of ultraviolet systems. Abbreviated as μWs/cm2.


The point at or near the middle of a scale or set of experimental results data in scientific analyses.

Midpoint Distributor

The lateral (horizontal) distribution system located at the interface where stratified anion and cation beds in a mixed bed ion exchange deionizer meet.

Milligram (mg)

One-thousandth of a gram (3.5 X 10-5 oz = 0.000035 oz).

Milligrams per Liter (mg/L)

A measure of concentration of a dissolved substance.     A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus, a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water, or 10 parts per million (10 ppm).

Milliliter (mL)

A unit of volume measure equal to 1/1000 liter (or one cubic centimeter); the volume occupied by one gram of pure water at 4 degrees C at 760 mm of pressure or standard atmospheric pressure.

Millimeter (mm)

A unit of length equal to 0.001 of an inch. The diameter of wires and tubing is measured in millimeters, as is thickness of plastic sheeting.


A unit of length equal to 10-3 microns (one thousandth of a micron), 10-6 millimeters, or 10-9 meters; correctly called a nanometer (nm).

Million-gallons per day (MGD) A measure of water flow.

Mineral (1)

An inorganic (nonliving, non-carbon containing) substance which occurs naturally in the earth and has a composition that can be expressed as a chemical formula and a set of characteristics (crystalline structure, hardness, etc.) common to all minerals.   Examples of minerals are sulfur, salt, and stone. Certain organic substances, such as coal, are also sometimes referred to as minerals. The word mineral is also used to refer to matter derived from minerals, such as inorganic ions found in water and reported as mineral content.

Mineral (2)

Term used in the water treatment industry to refer to naturally-occurring inorganic cation exchangers formerly used in water softeners - as opposed to the synthetic organic resins used today for water softening.

Mineral Acidity

Acidity in water due to the presence of strong inorganic acids such as hydrochloric, nitric, and sulfuric acids as opposed to weak acidity due to such acids as carbonic acid or acetic acid. Mineral acidity is usually expressed in water analysis as FMA (free mineral acidity).

Mineral Salt

A chemical compound formed by the combination of a mineral acid and a base. Minerals from dissolved rock exist in water in the form of dissolved mineral salts. An excess of mineral salts can give water a disagreeable taste or even be harmful to human health.

Mineral Water

Water which is naturally or artificially impregnated with mineral salts or gases (carbon dioxide). The term is also used to designate bottled water that contains no less than 250 ppm total dissolved solids (TDS) and originates from a protected groundwater source.

Mineral-Free Water

Water produced by either distillation or deionization.     This term is sometimes found on labels of bottled water as a substitute term for distilled or deionized water.


The microbial conversion of an element from an organic to an inorganic state.

Miners Salt

Another name for mined rock salt.


Able to be mixed together or dissolved into each other to produce a homogenous substance.

Mixed Bed

The intermix of two or more filter or ion exchange products in the same vessel during a service run.     The most common use is in ion exchange systems having a 40/60 percent cation to anion resin bed such as that for a deionization polisher unit. In filtration, there may be an intermix of two or more media in a single tank with each stratified into separate layers.

Mixed Liquor

A mixture of activated sludge and waters containing organic matter undergoing activated sludge treatment in the aeration tank of a waste water treatment system.

Mixed Media

The use of two or more media products in a single filtration loose media bed where the products are intermixed--rather than in stratified layers.     For example, the intermix use of calcite and magnesia in pH modification.


In statistics, the most frequently occurring number in a set of numbers.  For example, in the set 1,2,4,4,4,4,6,8,10, the number 4 is the mode.


Use of mathematical equations to simulate and predict real events and processes.


The membrane element and its housing in a reverse osmosis unit.

Molar of Molarity

A molar solution consists of one-gram molecular weight of a compound dissolved in enough water to make one liter of solution. A gram molecular weight is the molecular weight of a compound in grams. For example, the molecular weight of sulfuric acid (H2SO4) is 98. A one M solution of sulfuric acid would consist of 98 grams of H2SO4 dissolved in enough distilled water to make one liter of solution.


Abbreviated as “mol”. A measure used in chemistry to describe the number and mass of constituent particles relative to the mass and number of particles in 12.00 grams of elemental carbon. Just as the term “dozen” indicates 12 items, the term “mole” indicates 6.022140857 x 1023 molecules. SEE ALSO Avogadro’s number.

Molecular Weight (MW)

The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. For example, the molecular weight of sulfuric acid (H2SO4) in grams is 98.


The smallest particle of an element or compound that retains all of the characteristics of the element or compound. A molecule is made up of one or more atoms.     The helium molecule, for example, has only one atom per molecule. Oxygen molecules (O2) have two atoms; ozone molecules (O3) have three atoms. Molecules found in chemical compounds often have many atoms of various kinds.


Trade name for a series of corrosion resistant alloys made of nickel and copper.


Measuring concentrations of substances in environmental media or in human or other biological tissues.

Monitoring Light Sensor

An indicator light, electrically or electronically activated, which is positioned in the effluent (product water) stream of a piece of water treatment equipment (deionizer, distiller, reverse osmosis unit, or electrodialysis unit) to detect and signal changes in the water quality which might indicate malfunction of the equipment.     Some lights remain on while water quality is within the desired range and go out if the quality of the water falls into the unacceptable range. Other sensors use red and green light signals.

Monitoring Wells

Wells used to collect groundwater samples for analysis to determine the amount, type, and spread of contaminants in groundwater.


A product trade name for a fully regenerated ion exchange mixed bed (strong acid cation H+ and strong base anion OH-).


Consisting of radiation or rays, such as ultraviolet rays, of a single wave length or of a very small range of wave lengths.


A molecule of low molecular weight capable of reacting with identical or different monomers to form polymers.


Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year.     These lakes and reservoirs usually become destratified during the mixing cycle, usually in the fall of the year.


Having a valence of one, such as the cuprous (copper) ion, Cu+. Also called univalent.



Most Probable Number (MPN)

Term indicating the number of organisms in a sampled water which, according to statistical theory, would most likely produce the results observed in the multiple tube fermentation bacteriological tests. Usually expressed as a number per 100 ml of water.

Mother Liquor

1. Residual brines, containing chiefly calcium and magnesium chlorides, obtained after the salt has been crystallized and removed from solution. The term "mother liquor" is widely used when salt is produced by use of vacuum pan and gainer operations. In the solar salt evaporation process, the term "bitterns" is often used in place of the term "mother liquor".     

2. A solution substantially freed from undissolved matter by a solid/liquid separation process, such as filtration or decanting.


Capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.

Motive Flow

The water flow rate (e.g., gallons per minute) through a venturi injector that provides the suction at the injection port of the injector to induce the flow of another liquid (such as a regenerant) or gas (such as air or ozone) into the flow of water.

Motor Efficiency

The ratio of energy delivered by a motor to the energy supplied to it during a fixed period or cycle. Motor efficiency ratings will vary depending upon motor manufacturer and usually will range from 88.9 to 90.0 percent.


Most probable number.


Maximum tolerated dose, the dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.


Material that is approximately round in shape and varies from pea-sized up to two or more inches in diameter.     This material forms in filters and gradually increases in size when not removed by the backwashing process.


Any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff.

Multifunctional Medium

A single filter or ion exchange medium used to treat water for the removal of more than one constituent. Examples are activated carbon for chlorine removal and sediment filtration, calcite for pH modification and filtering of precipitated iron, or cation resin for reduction of dissolved iron as well as hardness removal.

Multilayered Bed

A media bed in which more than one filter or ion exchange medium is used in the same vessel, with each medium retaining its stratified position as a layer -  even after specified backwashing is performed -  due to differences in media densities.

Multiple Use

Use of land for more than one purpose; i.e., grazing of livestock, wildlife production, recreation, watershed, and timber production. Could also apply to use of bodies of water for recreational purposes, fishing, and water supply.

Multiport  Valve

A master control valve used in a filter, deionizer, or water softener to control all the necessary steps in the regeneration process or the backwashing and rinse down of filters. Term originated by the Permutit Company of New York.

Multistage Model

Mathematical model based on the multistage theory of the carcinogenic process, which yields risk estimates either equal to or less than the one-hit model.

Multistage Pump

A pump that has more than one impeller. A single-stage pump has one impeller.

Municipal Sewage

Wastes (mostly liquid) originating from a community; may be composed of domestic waste waters and/or industrial waste waters.

Municipal Softening

A hardness reduction process performed at municipal central treatment plants to deliver water in the range of 5 to 12 grains per gallon total hardness.

Municipal Water

Water that has been processed at a central plant to make it potable or "safe to drink" and which is then distributed to homes and businesses via water mains.     Either public agencies or private companies can be involved in providing "municipal water". The term is a general one used to refer to the common source of water in most urban and suburban areas--as opposed to water obtained from separate proprietary sources such as private wells.


Mushing of water softener salt occurs when salt pellets break down into their crystallized form. If a water softener brine tank is caked with salt or if a ridge of salt appears in the unit, the salt has either mushed or bridged, or both. Both salt mushing and salt bridging conditions prevent proper circulation of salt in the unit and require that the brine system be cleaned.


An agent that causes a permanent genetic change in a cell other than that which occurs during a normal genetic recombination.


The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cell.

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Updated on Mon, 29 Jun 2020 by Amy

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