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Residential Water Glossary

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

Activated Carbon – A granular material usually produced by the roasting of cellulose base substances, such as wood or coconut shells, in the absence of air. It has a very porous structure and is used in water conditioning as an adsorbent of organic matter and certain dissolved gases. Sometimes called “activated charcoal”.

Adsorbtion – The process in which matter adheres to the surface of the adsorbent.

Aeration – The process in which air is brought into intimate contact with water, often by spraying water through air or by bubbling air through water. Aeration may be used to add oxygen to the water for oxidation of matter such as iron or to cause the release of dissolved gases such as carbon dioxide or sulphur from the water.

Alkalinity – The quantitative capacity of a water or water solution to neutralize an acid. It is usually measured by titration with a standard acid solution of sulfuric acid and expressed in terms of its calcium carbonate equivalent.

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

Anion Exchange – An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. In demineralization, for example, bicarbonate, chloride and sulfate anions are removed from solution in exchange for a chemically equivalent number of hydroxide anions from the anion exchange resin.

Aquifer – A layer or zone below the surface of the earth which is capable of yielding a significant volume of water.

Atom – The smallest particle of an element that can exist either alone or in combination with smaller particles of the same element or of a different element.

Attrition – The process in which solids are worn down or ground down by friction, often between particles of the same material. Filter media and ion exchange materials are subject to attrition during backwashing, regeneration and service.

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

Bacteria – Unicellular micro-organisms which typically reproduce by cell division. Although usually classed as plants, bacteria contain no chlorophyll.

Bacteriostatic – A feature of a carbon filter that is supposed to inhibit the growth of bacteria within the filter – usually by the addition of silver.

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

Bed – The ion exchange or filter media in a column, in a tank or operational vessel.

Bed Depth – The height of the ion exchange or filter media in the vessel after preparation for service.

Boiling Point – The temperature at which a substance begins to change from a liquid state to a gaseous or vapor state.

Brackish Water – Water containing more than 1000mg/l of dissolved solids is generally considered to be brackish.

Brine (R.O.) – Same as reject water. One of two streams of fluids generated by a reverse osmosis unit. It contains the impurities removed from the feed water.

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

Calcium (Ca) – One of the principal elements making up the earth’s crust, the compounds of which, when dissolved, make water hard. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are a means of clearly identifying hard water.

Calcium Hypochlorite (CaCI2O2) – A chemical compound used as a bleach and a source of chlorine water treatment; specifically useful because it is stable as a dry powder and can be formed into tablets.

Capacity – An expression of the quantity of an undesirable material which can be removed by a water conditioner between servicing of the media (i.e. cleaning, regeneration and replacement) as determined under standard test conditions. In ion exchange water softeners, the capacity is expressed in grains of hardness removal between successive regenerations and related to the pounds of salt used in regeneration. For filters, capacity may be expressed in the length of time or total gallons delivered between servicing.

Caustic Soda – the common name for sodium hydroxide.

Cation – An ion with a positive electrical charge, such as calcium, magnesium and sodium.

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

Cellulose Acetate (CA) and Cellulose Triacetate (CTA) – A family of synthetic materials based on cellulose used to make reverse osmosis membranes. While CTA is superior to CA, under adverse water conditions both are effective in removing a wide spectrum of impurities from water. The disadvantage of cellulose-type membranes is that they are subject to bacterial attack, particularly in unchlorinated water supplies. CTA has superior bacterial resistance.

Channeling – The flow of water or other solution in a limited number of passages in a filter or ion exchange bed instead of distributed flow through all passages in the bed.

Chloramines – Chemical complexes formed from the reaction between ammonia and chlorine. They are presently being used to disinfect municipal water supplies because, unlike chlorine, they do not combine with organics in the water to form potentially dangerous carcinogens such as trihalomethanes (THMs). Chloramines can exist in three forms, the proportions of which depend on the physical and chemical properties of the water. Water containing chloramines may not be used for fish or kidney dialysis equipment.

Chlorides (CI) – an ion which forms acids when combined with hydrogen and salts when combined with metal ions. Chlorides can be corrosive and impart a salty taste to water.

Chlorine (CI2) – A gas widely used in the disinfection of water and an oxidizing agent for organic matter, iron, etc.

Coagulant – A material, such as alum, which will form a gelatinous precipitate in water and cause the agglomeration of finely divided particles into larger particles which can then be removed by settling and/or filtration.

Colloid – Very finely divided solid particles which will not settle out of a solution; intermediate between a true dissolved particle and a suspended solid which will settle out of solution. The removal of colloidal particles usually requires coagulation to form larger particles which may be removed by sedimentation or filtration.

Compensated Hardness – A calculated value based on the total hardness – the magnesium to calcium ratio and the sodium concentration of a water. It is used to correct for the reductions in hardness removal capacity caused by these factors in cation exchange water softeners. No single method of calculation has been so widely accepted.

Conductivity – The quality or power to carry electrical current. In water, the conductivity is related to the concentration of ions capable of carrying electrical current.

Contact Time – The length of time water is in direct contact with activated carbon (R.O.) or chlorine (chlorination system). This is a major factor in determining how effectively impurities will be removed.

Corrosion – The destructive disintegration of a metal by electrochemical means.

Cycle Time – The amount of time in seconds elapsed between pump start and pump shut-down.

Dechlorination (DI) – The removal excess chlorine residual, often after super-chlorination.

Deionization (DI) – The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure. First, positively charged ions are exchanged for a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed by an ion exchange resin for a chemically equivalent amount of hydrogen ions. The hydrogen and hydroxide ions introduced in this process unit to form water molecules. The term is often used interchangeable with demineralization.

Disinfection – A process in which pathogenic, disease-producing bacteria is killed. May involve disinfecting agents such as chlorine or physical processes such as heating and ultraviolet light.

Dissolved Solids – The weight of matter in true solution in a stated volume of water. Includes both inorganic and organic matter and is usually determined by weighing the residue after evaporation of the water at 105ºF or 40.6ºC.

Distillation – The process in which a liquid, such as water, is converted into its vapor state by heating and the vapor cooled and condensed to the liquid state and collected. Used to remove solids and other impurities from water. Multiple distillations are required for extreme purity.

DNA – Deoxyribonucleic acid constituting the genetic material of the chromosome in a cell, responsible for reproductive characteristics.

Drawdown – The amount of water delivered by the storage tank between pump shut-down and pump start.

E.Coli (Escherichia Coli) – One of the members of the coliform group of bacteria indicating fecal contamination.

Effluent – The stream emerging from a unit, system or process such as the softened water from an ion exchange softener.

Exhaustion – The state of an ion exchange material in which it is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions. The exhaustion point may be defined in terms of a limiting concentration of matter in the effluent or, in the case of demineralization, in terms of electrical conductivity.

Fecal – Matter containing or derived from animal or human waste.

Feed Pressure – The pressure at which water is supplied to the R.O. module.

Feed Water – A term which refers to the water supply that is put into a water treatment system for processing (removal of impurities).

Flocculation – The agglomeration of finely divided, suspended solids into larger, usually gelatinous, particles. The development of a ‘floc’ after treatment with a coagulant by gentle stirring or mixing.

Flow Control – A device designed to limit the flow of water or regenerant to a predetermined value over a broad range of inlet water pressures.

Flow Rate – The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in gallons per minute.

Flux – The flow rate of water through reverse osmosis membranes, per square foot of surface.

Fouling – The process in which undesirable foreign matter accumulates in a bed of filter media or ion exchanger, clogging pores and coating surfaces and thus inhibiting or retarding the proper operation of the bed.

Freeboard – The vertical distance between a bed of filter media or ion exchange material and the overflow or collector for backwash water. The height above the bed of granular media available for bed expansion during backwashing. May be expressed either as a linear distance or a percentage of bed depth.

Grain (gr) – A unit of weight equal to 1/7000 of a pound or 0.0648 gram.

Grain per Gallon (gpg) – A common basis for reporting water analysis in the United States and Canada. One grain per U.S. gallon equals 17.12 milligrams per liter (mg/l) or parts per million (ppm). One grain per British (Imperial) gallon equals 14.3 mg/l or ppm.

Greensand – A natural mineral, primarily composed of complex silicates, which can be coated with manganese oxide to form a catalytic absorptive surface. This surface is used to attract ferrous iron and manganese as well as to absorb dissolved oxygen which is used to oxidize iron, manganese or sulphur.

Hardness – A characteristic of natural water due to the presence of dissolved calcium and magnesium. Water hardness is responsible for most scale formation in pipes and water heaters and forms insoluble “curd” when it reacts with soaps. Hardness is usually expressed in grains per gallon (gpg), parts per million (ppm) or milligrams per liter (mg/l), all as calcium carbonate equivalent.

Hard Water – Water with a total hardness of 1 gpg or more as calcium carbonate equivalent.

Hydrologic Cycle – The natural water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere.

Hydrogen Sulfide (H2S) – A gas characterized by an offensive odor, commonly referred to as “rotten egg” odor. Flammable and poisonous in high concentrations, corrosive to most metals and can even tarnish silver. Detectable by most people in concentrations as low as 0.5 ppm.

Hydrocharger – Trade name of a particular type of air induction or injector valve.

Hydrolysis – The chemical degradation of an R.O. membrane in water due to certain conditions such as high pH. Cellulose based membranes are quite susceptible to hydrolysis while the TFC type are virtually immune.

Influent – The stream entering a unit, stream or process, such as the hard water entering an ion exchange water softener.

Ion – An atom, or group of atoms, which function as a unit and have a positive or negative electrical charge due to the gain or loss of one or more electrons.

Ion Exchange – A reversible process in which ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution; the direction of the exchange depends upon the affinities of the ion exchanger for the ions present and the concentrations of the ions in the solution.

Iron (Fe) – An element often found dissolved in ground water (in the form of ferrous iron) in concentrations usually ranging from 0-10 ppm (mg/l). It is objectionable in water supplies because of the staining caused after oxidation and precipitation (as ferric hydroxide); because of the tastes; and because of unsightly colors produced when iron reacts with tannins in beverages such as coffee and tea.

Iron Bacteria – Organisms which are capable of utilizing ferrous iron from the water or from steel pipe in their metabolism precipitating ferric hydroxide in their sheaths and gelatinous deposits. These organisms tend to collect in pipelines and tanks during periods of low flow and to break loose in slugs of turbid water to create staining, taste and odor problems.

Magnesium (Mg) – One of the elements making up the earth’s crust, the compounds of which, when dissolved in water, make water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.

Manganese (Mn) – An element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentration. Causes black stains and other problems similar to iron.

Manganese Greensand – Greensand which as been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power and is often used in the oxidation and precipitation of iron, manganese and/or sulphur and their removal from water.

Mechanical Filtration – The process of removing suspended particles from water by a straining action. The finest mechanical filters can remove bacteria as small as 0.2 microns.

Media –The selected materials in a filter that form the barrier to the passage of certain suspended solids or dissolved minerals. (Singular of media is medium).

Milligrams per Liter (mg/l) – A unit concentration of matter used in reporting the results of water and wastewater analysis. In dilute water solutions, it is practically equal to parts per million but varies from the ppm in concentrated solutions such as brine. As most analysis are performed on measured volumes of water, the mg/l is a more accurate expression of the concentration and is the preferred unit of measure.

Micron – A linear measure equal to one millionth of a meter or 0.0003937 inches. The symbol for the micron is the Greek letter µ.

Micron Rating – The term applied to a filter or filter medium to describe the particle size above which all suspended solids will be removed throughout the rated capacity. As used in industry standards, this is an “absolute” not “nominal” rating. (Refer to S-200, Recommended Industry Standards for Household & Commercial Water Filters.)

Mineral – A term applied to inorganic substances such as rocks and other matter found in the earth strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals such as the inorganic ions found in water. The term has been incorrectly applied to ion exchangers, even though most of the modern materials are organic ion exchange resins.

Mineral Salts – The form in which mineral from dissolved rock exist in water. Same as Total Dissolved Solids. This is the so-called inorganic form of minerals. In excess, they cause water to have a disagreeable taste. Some are harmful to human health.

Molecular Weight – The sum of the atomic weights of the individual atoms (from a periodic chart) that make up a molecule of a particular substance (e.g. H2O) H=1 atomic weight, 0=16 atomic weight, therefore, molecular weight = 2 + 16 = 18).

Nanometer – A measure of a wavelength in the electromagnetic spectrum. One nanometer equals 109 meter.

Neutralization – In general, the addition of either an acid or a base to a solution as required to produce a neutral solution. The use of alkaline or basic materials to neutralize the acidity of some water is common practice in water conditioning.

Organic Iron – A ferrous iron molecule which is enveloped in an organically complex molecule that resists oxidation. May be present in water that contains a great deal of colored colloidal turbidity (sediment).

Organics – Any of the compounds whose chemical structure is based on carbon (e.g. carbon dioxide, wood, sugar, protein, plastics, methane, THM, TCE, etc.).

Osmosis – A process of diffusion of a solvent, such as water through a 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. (See Reverse Osmosis.)

Osmotic Pressure – The pressure created by the tendency of water to flow in osmosis. Every 100 ppm of TDS generates about 1 pound per square inch (psi) of osmotic pressure. This osmotic pressure must first be overcome by the water pressure for the reverse osmosis membrane to be effective.

Oxidation – A chemical process in which electrons are removed from an atom, ion or compound. The addition of oxygen is a specific form of oxidation. Combustion is an extremely rapid form of oxidation while the rusting of iron is a slow form.

Oxidizing Agents – Any substance that oxidizes another substance and is itself reduced in the process. Common examples include: oxygen, chlorine, potassium permanganate, hydrogen peroxide, iodine and ozone.

Ozone (O3) – An unstable form of oxygen occurring naturally in the upper atmosphere or artificially produced because of its strong oxidizing or disinfection characteristics.

Particle Size – As used in industry standards, the size of a particle suspended in water as determined by its smallest dimension, usually expressed in microns.

Parts per Million (ppm) – A common basis for reporting the results of water waste water analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, on part per million is practically equal to one milligram per liter, which is the preferred unit. 17.12 ppm equals one grain per U.S. gallon.

Pathogen – An organism which may cause disease.

PCB (Polychlorinated Biphenyls) – A highly toxic organic contaminant found in water supplies which is suspected of causing cancer in humans.

pH – or the potential of hydrogen ion activity or concentration. pH is a measure of the intensity of the acidity or alkalinity of water on a scale from 0 to 14, with 7 being neutral. When acidity is increased, the hydrogen ion concentration increases, resulting in a lower pH value. Similarly, when alkalinity is increased, the hydrogen ion concentration decreases, resulting in higher pH. The pH value is an exponential function so that pH 10 is 10 times as alkaline as pH 9 and 100 times as alkaline as pH 8. Similarly, a pH 4 is 100 times as acid as pH 6 and 1000 times as acid as pH 7.

Potassium Chloride (KCI) – a compound consisting of potassium and chloride, becoming increasingly popular as a substitute for sodium chloride in regenerating water softeners.

Potassium Permanganate (KMnO4) – A powerful oxidizing agent consisting of dark purple crystals with blue metallic sheen. Explosive in contact with sulfuric acid or hydrogen peroxide. Increases flammability of combustible materials. Used to renew the black manganese oxide coating on greensand media.

Precipitate – To cause a dissolved substance to form a solid particle which can be removed by settling or filtering such as in the removal of dissolved iron by oxidation, precipitation and filtration. The term is also used to refer to the solid formed and the condensation of water in the atmosphere to form rain or snow.

Pre-treatment – Whatever alterations of the raw feed water are required to prevent damage to the reverse osmosis membrane.

Product Water – The pure water that has been separated from the feed water stream by the reverse osmosis membrane.

Pumping Rate – The amount of actual water that can be drawn from a pressure system expressed in gallons per minute (gpm) obtained by dividing the drawdown (gallons) by the cycle time (seconds) and multiplying the result by 60 (seconds).

Quartz – A high grade of glass made using quartz sand.

Raw Water – Untreated water or any water before it reaches a specific water treatment device or process.

Recovery – The amount of product water as compared with the total amount of feed water. This will give a measure of the efficiency of operation. For example, starting with 10 gallons of feed water, if 6 gallons is product water and 4 gallons reject water, the recovery is 60%.

Regenerant – A solution of a chemical used to restore the capacity of an ion exchange or oxidation system.

Regeneration – In general, includes the backwash, brine and fresh water rinse steps necessary to prepare a water softener exchange bed for service after exhaustion. Specifically, the term may be applied to the “brine” step in which the sodium chloride solution is passed through the exchanger bed. The term may also be used for similar operations relating to demineralizers and certain filters.

Rejection – The percentage of TDS removed from the feed water. Typically greater than 90% rejection is achieved with reverse osmosis.

Reject Water (same as Brine) – That portion of the feed water that does not pass through the R.O. membrane and which carries the remaining impurities to the drain.

Residual Chlorine – Chlorine remaining in a treated water after a specified period of contact time to provide protection throughout a distribution system. The difference between the total chlorine added and that consumed by oxidizable matter.

Resin – Synthetic organic ion exchange material such as the high capacity cation exchange resin widely use in water softeners.

Reverse Osmosis (R.O.) – A process that reverses, by the application of pressure, the flow of water in the natural process of osmosis so that the water passes from the more concentrated to the more dilute solution through a semi-permeable membrane.

Sediment – The sum of particles of dirt, clay, silt and vegetation which float or are suspended in water and can be removed by mechanical filtration. See Turbidity.

Semi-permeable – A term which applies to special materials, both natural and synthetic, which allow certain substances such as water to pass through (to permeate) while blocking or rejecting the passage of other substances such as dissolved solids and organics.

Service (Peak) Flow Rate – The greatest amount of water (expressed in gallons per minute) that a particular filter can effectively process based on short pump runs of less than 10 to 15 minutes maximum.

Sequester – A chemical reaction in which certain ions are bound into a stable, water soluble compound, thus preventing undesirable action the ions.

Soap – One of a class of chemical compounds which possesses cleaning properties, formed by the reaction of a fatty acid with a base of alkali. Sodium and potassium soaps are soluble and useful but can be converted to insoluble calcium and magnesium soaps (curd) by the presence of these hardness ions in water.

Soda Ash – 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 conditioning process.

Total Hardness – The sum of all hardness constituents in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution but may include small amounts of metals, such as iron, which can act like calcium and magnesium in certain reactions (see Hardness).

Toxic – Having an adverse physiological effect on man.

Toxic Metals – Elemental metals that find their way into water supplies from natural and industrial sources and which are detrimental to human health (e.g. lead, cadmium, mercury, arsenic).

Toxic Organics – Carbon-based chemicals which are frequently found in our water supplies and are harmful to human health. They are usually from agricultural and industrial effluents and hazardous waste dumps (e.g. TCE, PCB, DCBP, pesticides, etc.).

Turbidity – Suspended biological, inorganic and organic particles in water which may be in sufficient amount to make the water seem cloudy (see Sediment).

Virus – The smallest form of life know to be capable of producing disease of infection, usually considered to be of large molecular size. They multiply by assembly of component fragments in living cells, rather than by cell division as do most bacteria.

Volatile Organic Chemical (VOC) – Chemicals or compounds with boiling points below 212ºF, facilitating their evaporation before water.

Water Softening – The removal of calcium and magnesium, the ions which are the principal cause of hardness, from water.

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