Back Pressure

Pressure which creates resistance against a flow of water.

Back Siphonage

A form of backflow which occurs due to negative pressure.


The flow of water in a pipe or line in a direction opposite to the normal flow.     Backflow is a problem if there is back siphonage or back pressure causing reverse flow from a cross connection.

Backflow Preventer

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

Background Level

In contaminant monitoring, the average presence of a substance in the environment, originally referring to naturally occurring phenomena.


A form of backflow which occurs due to negative pressure.


Single-celled organisms (singular form=bacterium) which lack well-defined nuclear membranes and other specialized functional cell parts and reproduce by cell division or spores.     Bacteria may be free-living organisms or parasites. Bacteria (along with fungi) are decomposers that break down the wastes and bodies of dead organisms, making their components available for reuse.     Bacterial cells range from about 1 to 10 microns in length and from 0.2 to 1 micron in width. They exist almost everywhere on earth. Despite their small size, the total weight of all bacteria in the world likely exceeds that of all other organisms combined.     Some bacteria are helpful to man, others harmful.


Any substance or agent which kills bacteria, both disease causing and nondisease causing.     Spores and nonbacterial microorganisms (e.g., algae, fungi, and viruses) are not necessarily killed by a bactericide.


Having the ability to inhibit the growth of bacteria without destroying the bacteria.     For example, silver-impregnated activated carbon will reduce bacterial colonization in a bed but not eliminate it.


A deflecting barrier to affect the flow pattern of water.


A 10- to 20-foot-long pipe equipped with a valve at the lower end.     A bailer is used to remove slurry from the bottom or the side of a well as it is being drilled.

Balanced Flow

A flow pattern which is controlled to achieve the flow specified for that water treatment system.


The power supply to activate and regulate voltage in an ultraviolet (UV) lamp.


A unit of pressure. One bar equals 14.5 pounds per square inch (psi), or about 0.987 standard atmospheres.

Barium Fouling

In ion exchange deionization, a condition where the cation exchanger resin becomes coated with a very insoluble coating of barium sulfate. This occurs in the decationization unit when regenerated with sulfuric acid, where a barium-bearing water is being processed.    Generally, the remedy must be to replace the cation resin and install upstream water softening to remove the barium prior to the deionization treatment.

Barrier filter

A mechanical filter that physically prevents passage of waterborne solids within a specific particle size range. Barrier filters can include various components such as screens, membranes, or granular media. A common barrier filtration strategy includes the use of a “tortuous path” where the physical pore size of the barrier component is leveraged along with the convoluted flow of water to enable electrostatic and intermolecular forces to act upon the solids allowing rejection of solids smaller than the actual pore size. SEE ALSO mechanical filter; depth filter; tortuous path.


A substance that accepts (binds) hydrogen ions thereby reducing the concentration of free hydrogen ions in solution and raising the pH. A base may be classified as strong or weak, depending on the degree it’s able to attract the hydrogen ion. Hydroxides of metal ions, such as sodium hydroxide and potassium hydroxide, are strong bases. Weak bases include ammonia and alkalinity ions such as carbonate and bicarbonate. Base strength can be determined from pKb tables, readily available in chemistry reference texts and from reputable sources online. The higher the pKb number, the stronger the base. SEE ALSO alkalinity.

Base Exchange

See Cation Exchange

Base Metal

A metal (such as iron) which reacts with dilute hydrochloric acid to form hydrogen.

Batch Treatment

A method in which a fixed quantity of water is processed through a single treatment device in a single vessel.

Baume (Be)

An arbitrary scale of specific gravities used in the graduation of hydrometers.     The Baume measurements were developed by the French chemist Antoine Baume .     For liquids heavier than water Be = 145 - (145 specific gravity); for liquids lighter than water, Be = (140 ö specific gravity) - 130.

Bay Salt

A relatively coarse salt made from seawater.

Bead (Resin Bead)

In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.

Bead Count

A method of evaluating the physical condition (quality) of the resin in a bed by determining the percent of whole, cracked, or broken beads in a wet sample of the resin.

Beaver Fever

Flagellate protozoan which is shed during its cyst stage into the feces of man and animals.     When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.

Becquerel (Bq)

The SI unit of radioactivity equal to one nuclear disintegration per second.     The becquerel supersedes the curie, which equals 3.7 X 10E+10 nuclear disintegrations per second. One becquerel (Bq) equals 27.03 picocuries (pCi).


The mass or volume of ion exchange resin or other media through which the water passes in the process of water treatment.

Bed Depth

The height of the resin or other media (excluding support material) in a bed, usually expressed in inches or centimeters.

Bed Expansion

The effect produced during backwashing when the resin or other medium becomes separated and rises in the tank or column.     Usually expressed as percent of increase of bed depth such as 25 percent, 50 percent, 75 percent, etc.

Bed Volume (BV)

A term used as a measurement of a volume of  incoming (feedwater) in gallons or liters,  equal to (in cubic feet or liters) the  volume of ion exchange or filter media product in a tank-including voids.  Example: one bed volume for a cubic foot bed would be equal to 7.48 U.S. gallons or 28.3 liters.  This term is used mainly in laboratory and in experimental testing rather than in equipment capacity ratings.

Bench Scale

Bench scale testing is usually conducted in the laboratory, but is a simulated test in which conditions are approximate to those with which the item will be used.

Best Available Technology (BAT)

The best technology treatment techniques, or other means which the administrator finds, after examination for efficacy under field conditions and not solely under laboratory conditions, that are available (taking cost into consideration).     For the purposes of setting MCLs for synthetic organic chemicals, any BAT must be at least as effective as granular activated carbon.

Best Management Practices (BMPs)

Structural, nonstructural, and managerial techniques that are recognized to be the most effective and practical means to control nonpoint source pollutants yet are compatible with the productive use of the resource to which they are applied.     BMPs are used in both urban and agricultural areas.

Beta-minus decay

A type of radioactivity where the nucleus of an atomic species changes or disintegrates (decays) via negatron emission an energetic negative electron being emitted.  Beta-minus decay produces a transformed daughter nucleus of one lower atomic number and the same mass number.

Beta-plus decay

A type of radioactivity where the nucleus of an atomic species changes or disintegrates (decays) via an energetic positron (a positive electron antiparticle) being created and emitted, along with a neutrino.  Beta-plus decay produces a transformed daughter nucleus of one lower atomic number and the same mass number.


An inadequacy in experimental design that leads to results or conclusions not representative of the population under study.


The HCO<sub>3</sub> ion.

Bicarbonate Alkalinity

The alkalinity of a water due to the presence of bicarbonate ions (HCO<sub>3</sub>-).

Bicarbonate Hardness

The hardness of a water due to the presence of calcium and magnesium bicarbonates, usually the major component of carbonate hardness or total hardness. Bicarbonate hardness is often referred to simply as carbonate hardness.

Bicarbonate of Soda

A common name, along with baking soda, for sodium bicarbonate (NaHCO<sub>3</sub>).


The retention and concentration of a substance by an organism.


Test which determines the effect of a chemical on a living organism.

Biochemical Oxygen Demand

The amount of oxygen (measured in mg/L) required in the oxidation of organic matter by biological action under specific standard test conditions.     Widely used to measure the amount of organic pollution in waste water and streams.


A chemical which can kill or inhibit the growth of living organisms such as bacteria, fungi, molds, and slimes. Biocides can be harmful to humans, too. Biocides kill spores of living organisms also, and since spores are the most resistant of all life forms, a biocide may be properly defined as a sterilizing agent.


The accumulation of a chemical in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides.


Subject to degradation (breakdown) into simpler substances by biological action.     For example: the breakdown of detergents, sewage wastes, and other organic matter by bacteria.


Decomposition of a substance into more elementary compounds by the action of microorganisms such as bacteria.


An accumulation of sessile microbial growth imbedded in a film of adhesive polymer and attached on the surface of a support material, such as the interior surface of water pipe or water storage vessels.     Bacteria within the film may be protected from the action of disinfectants and sanitizers.

Biogas (Methane)

A colorless, odorless, flammable gas consisting of the hydrocarbon (CH<sub>4</sub>) 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.

Biological Growth

The activity and growth of any and all living organisms.

Biologically Activated Carbon

Activated carbon which maintains active microbiological growth to aid in the degradation and reduction of organics that have been adsorbed on the surface and in the pores of activated carbon.     Biological activation of carbon can be enhanced by enriching the feedwater with air or ozone.


A process of adding nutrients to ground water to speed up the natural process in which bacteria breakdown gasoline and other petrochemicals into harmless compounds.


An agent similar to a bacteriostat but prevents the growth of (but not necessarily destroys) all living organisms.


An overall term for all living organisms in an ecosystem.


Conversion of a substance into other compounds by organisms; includes biodegradation.


The trade name for a manganese dioxide-coated volcanic aluminum silicate (pumicite) used as an oxidizing-catalyst filter for iron and manganese reduction.

Bitterns (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.


Having a valence of two. Also called divalent.

Black Water

Liquid and solid human body waste and the carriage water generated through toilet usage.


A bottle containing only dilution water or distilled water; the sample being tested is not added. Tests are frequently run on a sample and a blank and the differences are compared.


A strong oxidizing agent and disinfectant formulated to break down organic matter and destroy biological organisms.     Commonly refers to a 5.25 percent nominal solution of sodium hypochlorite (household bleach) which is equivalent to 3 percent to 5 percent available free chlorine (strength varies with shelf life).     Sodium hypochlorite is also available commercially in concentrations of between 5 percent and 15 percent available chlorine. Dry bleach is a dry calcium hypochlorite with 70 percent available chlorine.

Blind Spots

Places in the filter medium or membrane where no filtration takes place.


The reduction or shutting off of flow due to filter medium or membrane fouling.

Block Carbon (Activated Carbon Block Filter)

Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants.     The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon.     Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of <i>Giardia</i> and <i>Cryptosporidium</i>.


1. The technique sometimes used for recycling concentrate back to the feed.     2. Contaminant leakage through or by the water treatment device.


The withdrawal of water containing a high concentration of solids from an evaporating water system (such as a boiler system) in order to maintain the solids-to-water concentration ratio within specified limits.     Blowdown is normally performed in boiler and cooling water operations. The term may also refer to removal of other solutions of undesirable quality from a system or vessel.

Blue-Green Algae (Cyanobacteria)

Single-celled organisms (singular=cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis.     Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae.     Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.

Boiler Water

A representative sample of the water or steam condensate circulating in a boiler system, taken after the generated steam has been separated and before the incoming feedwater or any added chemical has become mixed with the sample to change its composition.     The quality of boiler feedwater must be carefully controlled to limits depending on the boiler pressure and horsepower rating.

Bone Char

A black pigment substance, with a carbon content of about 10 percent, made by carbonizing animal bones.     Bone char is used for decolorizing sugar and water treatment. It has been used as a selective anion exchanger for fluoride and arsenic reduction.


The cover on a gate valve.

Bored Well

A shallow (10 to 100 feet or 3 to 30 meters) large-diameter well (8 to 36 inches or 20 to 90 cm.) constructed by hand-operated or power-driven augers.

Bottled Artesian Water

Bottled water from a well tapping a confined aquifer in which the water level stands above the water table. Bottled artesian water shall meet the requirements of bottled natural water.

Bottled Distilled Water

Bottled water which has been produced by a process of distillation and meets the definition of purified water in the most recent edition of the United States Pharmacopeia.

Bottled Fluoridated Water

Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Mineral Water

Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Natural Water

Bottled spring, mineral, artesian, or well water which is derived from an underground formation, and is not derived from a municipal system or public water supply.

Bottled Spring Water

Bottled water derived from an underground formation from which water flows naturally to the surface of the earth, or is pumped through a borehole from a spring source. Bottled spring water shall meet the requirements of bottled natural water.

Bottled Water

Water that is placed in a sealed container or package, and is offered for sale for human consumption or other consumer uses.     Bottled water may be with or without natural or added carbonation, and may be prepared with added flavors, extracts, and/or essences derived from a spice or fruit and comprising less than one percent by weight of the final product.     Said products shall contain no sweeteners, acidulants, or additives other than said flavors, extracts, or essences.

Bottled Water Plant

Any place or establishment in which bottled water is prepared for sale.

Brackish Water

Water containing dissolved solids in the range of 1,000 to less than 15,000 parts per million.

Brake Horsepower

1. The horsepower required at the top or end of a pump shaft (input to a pump).     2. The energy provided by a motor or other power source.


A metal alloy of copper, zinc, and usually some lead. Brass is harder and stronger than copper because of its zinc content; lead contributes malleability and ductility.     Machined brass plumbing products are often made from Copper Development Association (CDA) 360 series brass which contains about 65 percent copper, 32 percent zinc, and 3 percent lead.

Breakpoint Chlorination

A chlorination procedure in which the chlorine is added until the chlorine demand is satisfied and a chlorine residual occurs.     The breakpoint is reached when a free chlorine residual is achieved. Further additions of chlorine produce a free chlorine residual proportional to the amount added.


The first appearance in the product water of an amount of the contaminant which exceeds the design performance criteria.


1. Bridging occurs in water softening when salt sticks together to form one large solid mass of pellets, or by the salt caking in a dry-salt brine tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The result of bridging is insufficient salt in the regenerant solution to properly regenerate the cation resin.     2. The ability of particles to form a crustlike film over void spaces within a filter medium or membrane.


A strong solution of salt(s) (usually sodium chloride and other salts too) with total dissolved solids concentrations in the range of 40,000 to 300,000 or more milligrams per liter. Potassium or sodium chloride brine is used in the regeneration stage of cation and/or anion exchange water treatment equipment.     Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCl by weight at 60 degrees Fahrenheit.

Brine Collector

A device used to gather and retrieve brine from a brine tank or ion exchange bed.

Brine Draw

Usually means the process of drawing a brine solution into a cation or anion exchange water treatment device during regeneration.

Brine Ejector (Eductor)

A device used to draw (or educt) brine from a brine tank and force (or eject) it into a cation and/or anion water treatment device.   Usually a component of the unit's control valve.

Brine Tank Grid

A perforated platform in the bottom section of a brine tank of home water softeners which creates a zone where water can come in contact with the lower side of the dry salt stored above. As the water reaches up to the salt layer, it creates the brine makeup for regeneration.


Tiny indentations (dents) high on the shoulder of a water pump's bearing race or bearing. A type of bearing failure.

British Thermal Unit (BTU)

The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Bromine (Br)

A nonmetallic usually univalent or pentavalent element that lies between chlorine and iodine in the halogen group of the periodic table.     Bromine has been used in swimming pools for disinfection and in cooling towers as a biocide, but its use in drinking water as a primary disinfectant has been limited because of uncertain effectiveness in the presence of organic material, ammonia, and other amines.

Brownian Movement

The random movement of microscopic particles suspended in a fluid.

Bubble Size

The average diameter of the gas (e.g., ozone or air) bubbles discharged from a diffuser at the bottom of the contactor in an ozone or aeration system.     Generally, the finer the bubble size and the longer the bubble resides (contacts) within the water, the greater will be the transfer of air or ozone to the water.


A chemical substance which stabilizes pH values in solutions.

Buffer Capacity

A measure of the capacity of a solution or liquid to neutralize acids or bases.     This is a measure of the capacity of water for offering a resistance to changes in pH.

Buffer Strips

Strips of grass or other close-growing vegetation that separate a waterway (ditch, stream, creek) from an intensive land use area (subdivision, farm); also referred to as filter strips, vegetated filter strips, and grassed buffers.


A material that upgrades or protects the cleaning efficiency of the surfactant.     Several types of compounds, with different performance capabilities, are used. Builders have a number of functions, principally inactivation of water hardness. This is accomplished either by sequestration, i.e., holding hardness minerals in solution, by precipitation, or by ion exchange. Complex phosphates are common sequestering builders. Sodium carbonate is a precipitating builder. Sodium aluminosilicate is an ion exchange builder.     Other functions of builders are to supply alkalinity to assist cleaning, especially of acid soils, to provide buffering so that alkalinity is maintained at an effective level, to aid in keeping removed soil from redepositing during washing, and to emulsify oily and greasy soils.

Built Detergent

A cleaning product containing both surfactant and builder.     Home laundering makes use of built detergents almost exclusively because of their effective performance. Ingredients used in formulations along with surfactant and builder include fluorescent whitening agent, antiredeposition agent, corrosion inhibitor, suds control agent, oxygen bleach, colorant, fragrance, enzyme, bluing, and processing aids. Not all of these ingredients are used in every built detergent. Inclusion of antiredeposition and whitening agents, corrosion inhibitor, colorant, fragrance, and processing aids is customary. Complex phosphates (especially sodium tripolyphosphate), sodium carbonate, and sodium silicate are the builders most commonly used. (Sodium silicate is also a corrosion inhibitor.) Borax and sodium citrate are used to a lesser extent.     Built detergents may be granular or liquid in form and produce high, medium, or low suds. Since built detergents are designed for doing laundry, they are classified as laundry detergents. They are also considered heavy duty. Those that are high sudsing are adapted to many nonlaundry household cleaning tasks, and are termed "all purpose."

Built Soap

A combination of soap and builder designed for general purpose use, especially laundering.     It also usually contains fluorescent whitening agent, colorant, and fragrance. The granule form of built soap represented a major development and, by the late 1930s, had largely replaced laundry soap in bar and chip form. However, it still presented the classical soap problems in hard water, and thus built soap granules rapidly lost market share when built detergents were marketed in the late 1940s. Today, built soaps are in very limited distribution.

Burnt Lime (CaO)

A calcined chemical material, calcium oxide.     Lime is used in lime and in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)<sub>2</sub>]. Lime is also called burnt lime; calyx; fluxing lime; quicklime; unslaked lime.

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Updated on Mon, 22 Jun 2020 by Jonathan

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