Water Terms glossary

Sortable A-Z Index

Absolute Filter Rating – Filter rating meaning that 99.9 % (or essentially all) of the particles larger than a specified micron rating will be trapped on or within the filter.

Absorption – The process in which one substance penetrates into the body of another substance, termed the absorbent. An example is the absorption of water into soil.

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. An acid is the opposite of an alkali, has a pH rating lower than 7.0, will turn litmus paper red, and has a sour taste.

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 ppm or mg/L of its calcium carbonate equivalent.

Activated Alumina – A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. It requires periodic cleaning with a regenerant such as alum, acid and/or caustic.

Activated Carbon – (1) This is a form of carbon that is processed to be more porous. It is effective in water filtration because the great surface area traps many water contaminants and takes them out of the water, but doesn’t clog up the water flow.

(2) A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous materials, such as coal, wood, or coconut shells, in the absence of air, creating a highly porous adsorbent material. Activated carbon is commonly used for dechlorination, organic chemical reduction and radon reduction, and is recognized by the US EPA as the best available technology for reduction of organic chemicals from drinking water.

Activated Silica – A negatively charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.

Adsorbate – Any substance that is or can be adsorbed. The liquid, gas or solid substance which is adsorbed as molecules, atoms, or ions.

Adsorbent – A water treatment medium, usually solid, capable of the adsorption of liquids, gases, and/or suspended matter. Activated alumina and activated carbon are common adsorbents used in water processing.

Adsorption – The physical process occurring when liquids, gases, or suspended matters adhere to the surfaces of, or in the pores of, an adsorbent media such as activated carbon. Adsorption is a physical process which occurs without chemical reaction.

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.

Aerobic – An action or process conducted in the presence of air, such as aerobic digestion of organic matter by bacteria.

Air Check – A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.

Air Gap – A clear vertical space through the free atmosphere between the lowest opening of any pipe or faucet conveying water or waste to a tank, plumbing fixture receptor, or other device and the flood level rim of the receptacle. An air gap is used to prevent cross connection between a water treatment device and a possible source of wastewater thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes usually require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.

Algae – Plant life (green scum) containing chlorophyll is usually found in stagnant surface water. Excessive growths may create taste and odor problems, and consume dissolved oxygen during decay. Sometimes it may be controlled in a pond by the addition of Potassium Permanganate. In a water supply system, chlorination followed by dechlorination is often used.

Alkali – A substance which creates a bitter taste and a slippery feel when dissolved in water and will turn red litmus paper blue. An alkali has a pH greater than seven and is the opposite of an acid. Highly alkaline waters tend to cause drying of the skin.
Alkalis may include the soluble hydroxide, carbonate, and bicarbonate salts of calcium, magnesium, potassium, and sodium. A hydroxide alkali may also be called a base.

Alkaline Ionized Water – Water which has undergone ionization and which has the properties of smaller cluster size, greater alkalinity and increased ORP (oxidation reduction potential).

Alkalinity – The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity. In the water industry, alkalinity is expressed in mg/l of equivalent calcium carbonate. There are three kinds of alkalinity: carbonate, bicarbonate, and hydroxide alkalinity. Total alkalinity is the sum of all three kinds of alkalinity. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.

Alum – The common name for aluminum sulfate [Al2 (SO4) x 14H2 O] which is often used as a coagulant in water treatment.
Amoeba – A single celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.

Anaerobic organism – An organism that can thrive in the absence of oxygen (air), such as bacteria in a septic tank.

Angstrom unit – A unit of wavelength of light equal to .00001 millimeter or .0001 microns.

Anion – A negatively charged ion in solution, such as bicarbonate, chloride, or sulfate. An anion [such as chloride (Cl-)] may result from the dissociation of a salt, acid, or alkali.

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 resin.

Anode – The positive pole of an electrolytic system. The metal goes into solution in a galvanic cell. Anodes of metals such as magnesium and 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.

ANSI – Abbreviation for American National Standards Institute.

Antioxidant – The ability of a substance to prevent or fight against the free radical damage caused by oxidation. If a substance has extra electrons that can be donated to the O-2 (free radical), then it is said to be an antioxidant.

Aqueous – Containing water; watery.

Aquifer – Natural underground reservoirs of porous layers of sand, rock or gravel.

Artesian – Describes underground water trapped under pressure between layers of impermeable rock. An artesian well is one that taps artesian water.

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

Backflow Preventor – A device or system installed in a water line to stop backflow from a non-potable source.

Backwash – The upflow or counter-current flow of water through a filter or ion-exchange medium, lifting the mineral bed and flushing away to the drain the particles of foreign matter that have been filtered from the water supply during the service cycle.

Bacteria – Unicellular microorganisms which typically reproduce by cell division. Although usually classed as plants, bacteria contain no chlorophyll. Many different types of bacterial organisms are often found in drinking water. Most municipally treated water is essentially bacteria free due to the addition of chlorine. Some forms of cyst type viruses have a degree of immunity to chlorine due to the cocoon-like shell around the virus. These types of organisms such as Giardia Cyst, Giardia Lamblia, and Cryptosporidium have a physical size of three to seven microns and can be effectively removed by sub-micron filtration. Some bacteria are helpful to man, others harmful.

Bacteriastatic Having the ability to inhibit the growth of bacteria without destroying them. For example, silver impregnated activated carbon will limit bacterial colonization but not eliminate it.

Bactericide – Any substance or agent which kills bacteria.

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

Base – An alkali that releases hydroxyl ions when dissolved in water. Bases reset with acids to form a neutral salt and water. In general they taste bitter rather than sour, and feel slippery and reverse the color changes produced by acids in indicators. For example, they turn litmus paper blue.

Bicarbonate Alkalinity – The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are procured, and the solution is alkaline.

Biocide – A chemical which can kill or inhibit the growth of lining organisms such as bacteria, fungi, molds, and slime. Biocides can be harmful to humans.

Biodegradable – Subject to degradation into similar substances by biological action . Examples include detergents, sewage, and other organic matter by bacteria.

Body fluids – Body fluids must maintain an exact pH level [7.365]. If it alters even one little bit you could die. Therefore the body is in a constant state of buffering its body fluids.

Brackish Water – Water containing bacteria between 1.000 and 15,000 ppm of dissolved solids.

Brine – A strong solution of salt(s), such as the sodium chloride or potassium brine used in the regeneration of ion exchange water softeners, but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.

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

Bypass – A connection or a valve system that allows untreated water to flow to a water system while a softener or filter 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.

Calcite – Calcium carbonate (CaCO3). A trade name for finely ground limestone, very high in calcium carbonate, which is used to raise the pH of acidic water.

Calcium ( Ca ) – One of the primary elements of the earth’s crust commonly found in water as a dissolved solid. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are means of clearly identifying hard water. It is sometimes referred to as lime.

Calcium Carbonate Equivalent – All forms of water hardness and other salts are commonly expressed in terms of calcium carbonate equivalents. This is necessary so that minerals of varying weight can be expressed in chemically equivalent terms.

Capacity – In a softener or deionizer it is the adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, etc., where the of these ratios represent the weight of the ions adsorbed and the denominators, the weight or volume of the adsorbent. It can also refer to the ability of any media to take up a specific contaminant and is rated by time over gallons. As to flow rates, it is the maximum or minimum flow obtainable under given conditions of media, temperature, pressure, velocity, etc.

Carbonaceous Exchangers – Ion exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, etc.

Carbon Dioxide – Water with a low pH value usually contains free carbon dioxide. Its presence is caused generally by absorption of carbon dioxide (CO2) from the air as water falls as rain, or by the decay of organic matter in the earth. Well water containing substantial quantities of CO2 has a resultant low pH and corrosive qualities. Carbon dioxide in water forms a weak carbonic acid.

Carcinogen – A substance that can cause cancer.

Cation – A positively charged particle or ion.

Ceramic Filter – A porous filter made of ceramic. Can be effective in cleaning the water at least of elements that are larger than water molecules. Some ceramics have been developed to be fine enough to filter bacteria and viruses.

Chloramines – Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Does not combine with organics to form trihalomethanes.

Chlorine – Widely used in the disinfection of water and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas, as a liquid in sodium, hypochlorite, or as a solid in calcium hypochlorite. In water, chlorine reacts with organics to form trihalomethanes (THM) which can cause cancer.

Code – Those regulations which the department having jurisdiction may lawfully adopt.

Coliform Bacteria – A group of organisms primarily found in human and animal intestines and wastes, and thus widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease producing) bacteria.

Colloid – Very finely divided solid particles larger than molecules but small enough that they will not settle out of a solution; intermediate between a dissolved particle and a suspended solid which will settle out of solution. Typically between 0.1 and 0.001 microns in diameter, it usually requires coagulation prior to filtration. colloidal (heme) iron may be removed by special anion resin.

Condensate – Water which has liquefied from steam.

Conductivity – The quality or power to carry electrical current; in water, the conductivity is related to the concentration of ions capable of carrying electrical current. The unit of measure is the mho, which is the reciprocal of resistivity which is the microhm.

Contact Time – The actual time which water remains in contact with an oxidizer, regenerant, or water conditioning media within a water treatment system. The amount of contact time determines the effectiveness of the system. Also called retention time.

Contamination – The addition of any physical, chemical, biological or radiological substance to water which reduces the value of the water, or interferes with its intended use.

Corrosion – The destructive disintegration of metals by electromechanical means. Corrosion of iron and steel is commonly called rusting.

Cross Connection – Any physical connection between two otherwise separated piping systems one of which contains potable water and the other of unknown or questionable safety, whereby flow may occur from one system to the other depending on the pressure differential between the two systems.

Cryptosporidium – A waterborne protozoan that forms cysts and causes acute illness in humans. This type of organism is resistant to chlorine and ultraviolet light but can be removed by one micron filtration.

Dealkalization – A process for the reduction of alkalinity in a water supply. It is generally accomplished by a chemical feed processor combined cation and anion exchange systems.

Dechlorination – The removal of excess or free chlorine from a water supply by adsorption with activated carbon or by catalytic type filter media.

Degassing – The removal of dissolved gasses from water such as carbon dioxide, methane, hydrogen sulfide, and oxygen. This can be done by subjecting the water to below atmospheric pressure, or by passing air through the water at atmospheric pressure.

Dehydration – The condition of not having sufficient water in your diet to keep your cells healthy. Many conditions can be attributed to dehydration, such as headache, low energy levels, low back pain, digestive problems, constipation, obesity, asthma allergies, arthritis, Type II Diabetes, and hypertension

Deionization – The removal of the 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 ions. 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. The cation resin is regenerated with an acid and the anion resin is regenerated with sodium hydroxide (caustic soda).

Density, Apparent (Density, Bulk) – The mass under specified conditions of a unit volume of a solid sorbent including its pore volume and inter-particle voids.

Desalination – The removal of dissolved inorganic solids (salts) from a solution such as water to make it free of dissolved salts. Typically accomplished by reverse osmosis, distillation, or electrodialysis.

Detergent – Usually refers to synthetic detergent, but can be any material with cleansing powers such as soap, alkaline materials, synthetic detergents, solvents, and abrasives. Synthetic detergents are known as surfactants which foam and act like soap but are not made from fatty acids and lye.

Drain Line – A pipe or conduit from a water conditioning unit used to carry backwash water, regeneration wastes and/or rinse water to a drain or waste system by gravity.

Drinking Water Standards – National Primary Drinking Water Standards are established by the U.S. Environmental Protection Agency (EPA) are health related and establish the maximum contaminant levels (MCL’s) for regulated substances in drinking water. A MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer’s tap. These standards relate to public water systems. National Secondary Drinking Water Standards are also issued by the EPA and pertain to aesthetic characteristics of water and are recommended only. Drinking Water Standards

Electrolyte – A chemical compound which dissociates or ionizes in water to produce a solution which will conduct an electric current. Could be an acid, base, or salt.
Filter – A device used to clean water by removing iron, silt, taste, odor, color, etc., before it is fed into the softener or supply lines of the consumer. Includes mechanical, adsorptive, oxidizing and neutralizing filters. Available as media beds in tanks or as cartridge type devices

Filtration – The process of passing water through a porous substance to remove solids in suspension. Available as media beds in tanks or as cartridge type devices

Flash Distillation – A distillation process in which hot water is introduced into a low pressure chamber causing some of the water to flash or quickly turn to steam.

Flow Controller – An in-line self pressure adjusting or orifice to regulate the flow of water or regenerate through a water conditioner.

Flow Rate – The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of gallons per minute per cubic foot of resin, or as milliliters per minute per milliliter of resin. If the flow rate is greater than it should be, the water will not be completely softened or filtered.

Flush Valve ( Flushometer ) – A self closing valve used for flushing urinals and toilets. This type of valve allows flow rates of 15-20 gpm for up to 10 seconds.

GAC – Granular Activated carbon.

Giardia Lamblia – A common protozoan found in water and is derived from animal droppings. It can cause contagious waterborne disease characterized by acute diarrhea. It is resistant to disinfectants such as chlorine, iodine, or ultraviolet light. Giardia can be removed by filters of four micron rating.

Groundwater – The term describing all subsurface water and the source of well water. It can be found in aquifers as deep as several miles.

Halogens – A family of elements that includes bromine, chlorine, fluorine, astatine, and iodine. They are very active chemically. They are commonly found as the ionic component in compounds with various other elements.

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. Temporary hardness, caused by the presence of magnesium of calcium bicarbonate, is so called because it may be removed by boiling the water to convert the bicarbonates to the insoluble carbonates. Calcium sulfate, magnesium sulfate, and the chlorides of these two metals cause permanent hardness.

Hard water – Water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.

Heterotrophic – Non-disease causing bacteria

Hydrogen Sulfide ( H2 S ) – A corrosive and flammable gas produced from decaying organic matter, commonly known as “sulfur”.

Hydrologic Cycle – The water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere. It is natures great water conditioner since all contaminants are left behind on the earth.

Hydroxyl – The term used to describe the anionic hydroxide radical (OH-) which is responsible for the alkalinity of a solution.

Inorganic Matter – Matter which is not derived from living organisms and contains no organically produced carbon; includes rocks, minerals and metals.

Ion – An atom, or group of atoms in a solution which function as a unit, and has a positive or negative electrical charge, due to the gain or loss of one or more electrons. It is smaller than a colloid.

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 concentration of the ions in the solution. The ion exchanger media is an insoluble permanent solid medium. for a product offering.

Ionization – The dissociation of molecules into simpler, electronically charged particles. It is related to the gaining or losing of electrons causing the atoms to become electronically charged.

KDF – A water treatment media employing copper and zinc alloy particulates which have a redox potential. KDF does not support the growth of bacteria and lasts up to twenty times longer than activated carbon. KDF 55 granules are effective in removing chlorine and other water-soluble heavy metals such as lead. KDF 85 is the choice for removing iron and hydrogen sulfide.
Legionella – A series of bacteria, including legionella pneumophila, which can cause pneumonia-like illness called Legionnaires disease after the American Legion convention in Philadelphia where the disease first drew attention. These bacteria have been found growing in hard water scale and thrive below 140 degrees Fahrenheit in water heaters, showers, humidifiers, etc. Infection is obtained by inhalation.

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. Insoluble scale is commonly formed when water containing calcium carbonate is heated. It also forms in cold water but precipitates at a higher pH.

Lime Softening – Often used by municipalities for partial reduction of water hardness. After the addition of baked lime, soda ash is added to form an insoluble precipitate which is filtered from the water. This method leaves five or more grains of hardness.

Magnesium – 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 ) – A element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentrations. It causes black stains in laundry and plumbing fixtures at concentrations higher than 0.05 mg/l. It is removed the same way as iron, by ion-exchange or oxidation and filtration.

MCL – Maximum Contaminant Level. A drinking water standard. The maximum amount of a contaminant allowed in drinking water.

MCLG – Maximum Contaminant Level Goal. The goal set for the maximum amount of a contaminant to be allowed in drinking water. Has not been approved to become the MCL.

Mechanical Filter – A filter primarily designed for the removal of suspended solid particles, as opposed to filters that remove contaminants by chemical means.

Micron – A linear measure equal to one millionth of a meter, or .00003937 inch. The symbol for the micron is the Greek letter “µ”. The smallest particle visible to the human eye is 40 microns. Most types of bacteria range from 0.05 to 10.0 microns in size.

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..

Mineral – A term applied to inorganic substances, such as rocks and similar matter found in the earth’s 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.

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.

Nanofiltration – A membrane process that treats water between reverse osmosis and ultrafiltration the filtration/separation spectrum. It can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color found in water. Nanofiltration may be used for selective removal of hardness ions.

Neutralizer – A common designation for alkaline materials such as calcite (calcium carbonate) or magnesia (magnesium oxide) used in the neutralization of acid waters. Alkaline water can also be neutralized by the addition of an acid. The neutral point of the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen and hydroxide ions.

NSF – Abbreviation for National Sanitation Foundation Testing Laboratory

Operating Pressure – The range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function. Usually 30-100 psi.

Organic – Having the characteristics of or being derived from plant or animal matter, as opposed to inorganic matter derived from rocks and minerals. Organic matter is characterized by its carbon-hydrogen structure.

Organics ( i.e., Organic Chemicals ) – Term used to describe any or all of the compounds with chemical structures based on carbon. Examples are hydrocarbons, wood, sugars, proteins, methane, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM) and trichloroethylene (TCE).

Osmosis – A process of diffusion of a solvent such as water through a semi-permeable 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. Osmosis causes the stronger solution to become more diluted and tends to equalize the opposing solutions.

Osmotic Pressure – The pressure and potential energy difference that exists between solutions on either side of a semi-permeable membrane. This pressure is caused by the tendency of water to flow in osmosis. Every 100 ppm (mg/L) of TDS produces about one pound per square inch of osmotic pressure. Osmotic pressure must first be overcome by water pressure in the reverse osmosis process.

Oxidation – A chemical process in which electrons are removed from an atom, ion or compound. The addition of oxygen is a speciform of oxidation. Combustion is an extremely rapid form of oxidation, while the rusting of iron is a slow form. Oxidation never occurs alone but always as a part of the oxidation-reduction (redox) reaction.

Oxidizing Agent – A chemical substance that brings about the oxidation of other substances in chemical oxidation and reduction reactions. Examples of oxidizing agents include oxygen, ozone, chlorine and peroxide.

Oxidizing Filter – A type of filter used to change the valence state of dissolved molecules, making them insoluble and therefore filterable. For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of a catalytic media such as manganese oxide and then filters the oxidized precipitant out of the water.

Ozone – An unstable form of oxygen (03), which can be generated by sending a high voltage electrical discharge through air or regular oxygen. It is a strong oxidizing agent and has been used in water conditioning as a disinfectant. It can be also produced by some types of ultraviolet lamps and during lightning storms.

Particulate – A term used to describe visible sediment particles, used as both singular and plural.

Parts Per Billion ( ppb ) – A basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per billion parts by weight of water or other solvent. One part per billion is equal to one microgram per liter, the preferred unit.

Parts Per Million ( ppm ) – A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.l ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.

pH ( potential of Hydrogen ) – An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral). e.g., pH 5 is 10 times the acidity of 6 and 100 times the acidity of 7. pH is a measure of intensity and not capacity. It is the logarithm of the reciprocal of the hydrogen ion concentration of a solution. The neutral point of 7 indicates the presence of equal concentrations of free hydrogen and free hydroxide ions.

Pharmaceutical Grade Water – The definition of six grades of water by the U.S. Pharmacopoeia is as follows: 1.) Purified water 2.) Water for injection 3.) Bacteriostatic water for injection 4.) Sterile water for inhalation 5.) Sterile water for injection 6.) Sterile water for irrigation.

Phenolphthalein – An acid-base indicator which produces no color in an acid solution but turns pink or red in an alkaline solution.

Physical Adsorption ( Van der Waals Adsorption ) – Binding of adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation.

Physical Stability – The quality which an ion exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.

Point of Entry ( POE ) – A water treatment device which installs at the main inlet to a building and acts as centralized treatment.

Point-of-Use ( POU ) – A water treatment system designed to connect at the actual point-of-use for water; countertop or undersink treatment systems.

Pores – The complex network of channels in the interior of a particle of a sorbent.

Positive Charge – The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.

Potable Water – Water which is considered safe and fit for human consumption, culinary and domestic purposes and meets the requirements of the health authority having jurisdiction.

Powdered Activated Carbon – Activated carbon in particle sizes predominantly smaller than 80 mesh.

PPB – The abbreviation for “parts per billion”.

PPM – The abbreviation for “parts per million”.

Precipitate – To cause a dissolved substance to form a solid particle that can be removed by settling or filtering. The term also refers to the solid thus formed.

Pressure Drop – A decrease in water pressure during its flow due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.

Protozoa – Any of a large group of mostly microscopic, one celled animals living chiefly in water. Many protozoa’s are parasitic and are higher on the food chain than the bacteria they eat.

Purification – The removal of undesirable matter from water or wastewater. It is the disinfection of water by the killing of microbial contaminants, such as coliform bacteria. A strict definition means the removal from water of all contaminants.

Putrefaction – Biological decomposition of organic matter by microbes with the production of ill smelling products. Usually takes place when there is a deficiency of oxygen.

Pyrogens – Substances which produce fever when introduced into humans. Being chemically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria. Pyrogenic means to cause heat.

Quartz Sleeve – Also called a quartz jacket, it is a clear, pure quartz sleeve that is installed around the high intensity ultraviolet lamp in an ultraviolet system. It retards less than 10 percent of the radiation dosage in contrast to the poorer results offered by glass.
Radium – Naturally occurring radioactive elements such as radium 226 and radium 228 created in the decay of the uranium and thorium series. It can be removed from water by cation exchange softening.

Radon – A short lived radioactive gas produced from decaying uranium that is soluble in water. Can be effectively removed by activated carbon filtration or serration. Radon is considered carcinogenic when inhaled by humans.

Raw Water – Untreated water from wells or from surface sources or any water before it reaches a water treatment device or process.

Reactivation ( Revivification ) – Oxidation processes for restoring the adsorptive properties of a spent sorbent such as activated carbon.

Redox – A shortened term for oxidation-reduction. A reaction where electrons are gained or lost and new elements are formed.

Rejection – In crossflow membrane filtration and deionization, it is the ability of the membrane to reject the passage of dissolved solids and other contaminants into the product water.

Residual – The amount of a specific material remaining in the water following a water treatment process. It may refer to material remaining as the result of incomplete removal such as hardness leakage, or to a substance meant to remain in the treated water such as residual chlorine.

Resin – Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners. Technical name- sulfonated co-polymer of styrene and divinyl benzene.

Reverse Osmosis – A process for the removal of dissolved ions from water, in which pressure is used to force the water through a semi-permeable membrane, which will transmit the water but reject most other suspended and dissolved materials. It is called reverse osmosis because mechanical pressure is used to force the water to flow in the direction that is the reverse of natural osmosis, namely from the dilute to the concentrated solution.

R.O. – The abbreviation for “reverse osmosis”.

Rust ( ferric oxide ) – A reddish product of corrosion sometimes found in water. Rust is formed as a result of electrochemical interaction between iron and oxygen in the presence of moisture.

Sand Filter – A treatment device or structure for removing solid or colloidal material of a type that cannot be removed by sedimentation. Such filters can be gravity rapid-rate or enclosed pressure type.

Salt – The common name for the specific chemical compound sodium chloride (NaCl), used in the regeneration of ion exchange water softeners. In chemistry, the term is applied to a class of chemical compounds which can be formed by the neutralization of an acid with a base.

Saturated Solution – A solution containing the maximum amount of the dissolved substance that such a solution can hold at this temperature.

Selective Ion Exchange – The use of a selective ion exchange medium with the property of removing specific ions from a solution.

Soda Ash – 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 treatment process.

Softened Water – Any water that is treated to reduce hardness minerals to 1.0 GPG (17.1 mg/L) or less, expressed as calcium carbonate.

Solvent – The liquid, such as water, in which other materials (solutes) are dissolved.

Sulfur – A yellowish solid chemical element. The term is also used as a slang expression to refer to water containing hydrogen sulfide gas (H2 S).

TCE ( Trichloroethylene ) – A toxic volatile organic chemical typically used as an industrial solvent.

TDS – The abbreviation for “total dissolved solids”.

Tannin – A naturally occurring substance in wood, grapeskins, seeds and stems. Is primarily responsible for the basic “bitter” component in wines. Acts as a natural preservative, helping the development and, in the right proportion, balance of the wine. Considered a pollutant when present in excess.

Thin-film Composite Membrane ( TFC ) – Reverse osmosis membrane produced with polyamide-based polymer. It is resistant to bacteria and can withstand a wide pH range. However, it cannot tolerate chlorine.

Total Chlorine – The total amount of chlorine is a solution, which includes the combined chlorine as well as the free available chlorine.

Total Dissolved Solids – The weight of solids per unit volume of water which are in true solution, usually determined by the evaporation of a measured volume of filtered water, and determination of the residue weight. TDS is expressed as ppm per unit volume of water. An electrical conductivity test provides only an estimate of the TDS since non-conductive substances cannot be measured by electrical means.

Total Hardness – The sum of all hardness components 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. These minerals are scale forming, affect taste and color of certain foods and react with soap to form insoluble soap curds.

Trihalomethanes ( THM ‘s) – A group of organic chemicals to known to be carcinogenic in more than trace amounts which are produced from chlorination. They reduce the germicidal activity of chlorine in alkaline water.

Turbidity – A measure of the amount of finely divided suspended matter in water, which causes the scattering and adsorption of light rays. Turbidity is usually reported in arbitrary nephalometric turbidity units (NTU) determined by measurements of light scattering. NTU should not exceed 0.5 in potable water. Turbidity can protect bacteria from sterilization.

Ultrafiltration – A membrane type system that removes small colloids and large molecules from solutions. Ultrafiltration removes particles in size range between 0.002 to 0.1 micron range. The process falls between reverse osmosis and microfiltration as far as the size of particles removed is concerned.

Uranium – A radioactive metallic element found naturally in combination with other materials. Uranium 238 is the most common form.

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 be cell division, as do most bacteria. Being parasitic infectious microbes, they are much smaller than bacteria.

Volatile Organic Compounds ( VOC ‘s) – Synthetic organic chemicals that vaporize at relatively low temperatures.

Water Conditioning – Virtually any form of water treatment designed to improve the quality of water, by neutralization, inhibition or removal of undesirable substances.

Water Hammer – The shock wave produced by the abrupt change of water flow through a piping system. Water hammer produces instantaneous multiple increases in the pressure normal to the system. The installation of a water hammer arrestor will absorb these shock waves.

Water Softening – The reduction or removal of calcium and magnesium ions which are the principal cause of hardness in water.

WQA – Water Quality Association. Many participants in the POU and POE water conditioning industry are members of this association.

Xylene – A volatile organic chemical (VOC) commonly used in industry as a solvent.

Zeolite – Naturally occurring or synthetic hydrated sodium alumina silicate with ion exchange properties. Zeolites have been largely replaced with synthetic organic cation ion exchange resins.
Modified Zeolites can be selectively charged with exchange minerals such as potassium and used to remove undesirable elements such as iron, hydrogen, sulfide, and manganese.