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Glossary of Water Treatment Terms

Glossary of Water Treatment Terms

Índice del contenido | Contents Index

Softening of water.

The reduction or elimination of calcium and magnesium ions, which are the main cause of hardness in water.

Softening with lime.

Process used in municipal plants for the partial reduction of water hardness. The method consists of adding slaked lime [Ca (OH) 2] to a source of hard water, to reduce the hardness concentration due to the precipitation of carbonates.


Assimilation of molecules or other substances within the physical structure of a liquid or a solid without chemical reaction. An example is the absorption of water in the soil.

Galvanic action

A form of corrosion that occurs when different metals come into contact in the presence of an electrolyte. This form of corrosion is accelerated when there is greater conductivity in the water due to the high concentrations of minerals dissolved in it. An example is when we join one metal pipe with fittings of a different metal and one begins to dissolve, first than the other.


The quantitative ability of a solution to neutralize an alkali or base. It is generally measured by titration with a standard sodium hydroxide solution, and is expressed in ppm or mg / L of calcium carbonate equivalent.

Total acidity

The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts.


A substance that releases hydrogen ions into water. Most acids dissolve common metals, and they also react with bases to form a neutral salt and water. An acid is the opposite of an alkali, it has a pH below 7.0 and a sour taste.

Water conditioning

Virtually any form of water treatment designed to improve water quality, by neutralizing, inhibiting, or removing undesirable substances.


Natural underground water deposits found below the earth’s surface (porous layers of sand, rock, or gravel).


Containing water or has a similar appearance to it.


Solid medium capable of adsorbing liquids, gases, or suspended matter. Activated Alumina and Activated Carbon are adsorbents commonly used in water treatment.


Liquid, gaseous or solid substance that can be adsorbed.


The physical process that occurs when liquids, gases, or suspended matter adhere to the surfaces or pores of an adsorbent medium such as activated carbon. Adsorption is a physical process that occurs without chemical reaction.


An action or process carried out in the presence of air, such as the aerobic digestion of organic matter by bacteria.


Water entering (feeding) into a water treatment device.

Oxidizing agent

Chemical substance that causes the oxidation of other substances. Examples of oxidizing agents include oxygen, ozone, chlorine, and peroxide.


It is the state in which an adsorbent or ion exchange medium is no longer capable of removing a specific contaminant or useful ion exchange. The depletion point is arbitrarily determined in terms of the presence or increase of a contaminant or the reduction in the quality of the effluent water.

Raw water

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

Pharmaceutical grade water

The definition of the grades of water for pharmaceutical use is defined by the Pharmacopeia of the United Mexican States. They are as follows:

1.) Purified water level 1

2.) Purified water level 2

3.) Water for the manufacture of injectables

4.) Sterile water for injectable use

5.) Bacteriostatic water for injectable use

6.) Sterile water for irrigation

7.) Sterile water for inhalation

Spare water

Treated water that is fed to a system to recover the level losses caused by evaporation, purging, splashing, etc.

Hard water

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

Drinking water.

It is the water that is considered safe and suitable for human consumption, for culinary and domestic purposes. It complies with the quality specifications established in the current official version of the Official Mexican Standard NOM-127-SSAA1-1994

Black waters

The sewage or wastewater are the fluids from sanitary waste; They are liquids with organic matter, fecal and urine, which circulate through the sewer.

Brackish water

Water that contains a concentration of dissolved solids greater than 1,000 ppm and less than 15,000 ppm.

Softened or soft water

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

Ultra pure water

Highly treated water with a low concentration of minerals and organics. It is usually used in the pharmaceutical and semiconductor industry. Ultrapure water is not considered sterile. There is no numerical standard that determines what “ultrapure” water is or is not.


The process in which air comes into contact with water, often by spraying water through a stream of air or by bubbling air through the water. Aeration can be used to add oxygen to water and cause the oxidation of materials such as iron, or to cause the release of dissolved gases like carbon dioxide or hydrogen sulfide from water.


A substance that creates a bitter taste and a soapy sensation when dissolved in water. An alkali has a pH greater than seven and is the opposite of an acid. Highly alkaline waters tend to dry out the skin. Alkalis can be soluble salts of calcium, magnesium, potassium, and sodium hydroxides, carbonates, and bicarbonates. An alkali hydroxide can also be called a base.


The quantitative ability 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.

In the water industry, alkalinity is expressed in mg / l calcium carbonate equivalent. There are three types of alkalinity: carbonate, bicarbonate, and hydroxide alkalinity. Total alkalinity is the sum of the three types of alkalinity.

Bicarbonate alkalinity

Alkalinity caused by the presence of bicarbonate ions (HCO3)

Total alkalinity

The total alkalinity of water is the sum of the three types of alkalinity caused by hydroxide ions (OH), carbonate (CO32-) and bicarbonate (HCO3), this is determined by valuation.


Unicellular or multicellular organisms, commonly found on the surface of aquatic bodies, produce their own food from photosynthesis. The excessive growth of algae can cause undesirable tastes and odors in the water, and its absence in aquatic bodies reduces the presence of oxygen in them.

Chemical feeder or dosing pump

A mechanical device designed to dose chemicals (such as chlorine, soda, iodine, etc.) into a water system.


The common name for aluminum sulfate [Al2 (SO4) x 14H2 O], which is often used as a coagulant in water treatment.

Activated alumina

It is an aluminum mineral granular medium that is subjected to a treatment to make it porous and highly adsorbent. Activated alumina removes various contaminants, such as fluoride, arsenic, and selenium.

When this is exhausted, a regeneration consisting of two steps is required, first caustic soda is added, followed by neutralization with sulfuric acid in a second step.


A single-celled protozoan widely found in fresh and salt water. Some types of amoebae cause diseases such as amoebic dysentery.


A unit of length equal to 0.00001 millimeters or 0.0001 microns.


Negatively charged ion that results from the dissociation of salts, acids or alkalis in aqueous solution.

Anion (Anion exchange)

Anions are negatively charged ions. An anion is the result of the dissociation of a salt, base or an alkali. Anion exchange is a process in which anions in a solution are exchanged for other anions by means of an ion exchange resin.


The positive pole of an electrolytic system. The metal that dissolves in a galvanic cell.

Sacrificial anode

An anode constructed of metals (magnesium, aluminum or zinc), usually installed in water heaters and other metals to prevent corrosion of the tank. Attaching an anode creates a galvanic cell that causes the magnesium and zinc to corrode more quickly, thus protecting the tank material.


Abbreviation for American National Standards Institute.


The most metamorphic coal containing the highest carbon content, it is black to steel gray in color with a bright hue.

Silica sand

It is a granular medium with a high content of silica in its composition, which gives it great hardness and comes in different granulometries depending on its application. In water treatment, the 20 × 30 granulometry is usually used.


Groundwater trapped under pressure between layers of impermeable rock.


Abbreviation for American Society of Mechanical Engineers.


Abbreviation for American Water Works Association. Most of the municipal water treatment plants in the United States are members of this association.


A yellowish solid chemical element. The term is also used as an expression to refer to water that contains gaseous hydrogen sulfide (H2S), which causes unpleasant “rotten egg in water” odors.


Unicellular microorganisms that typically reproduce by cell division, most are non-photosynthetic. Different types of bacterial organisms are regularly found in drinking water. Most municipal treated water is essentially free of bacteria due to the addition of chlorine. These types of microorganisms have a physical size of 0.02 to 2 microns and can be effectively removed by filtration (microfiltration) or ultraviolet light.

Coliform bacteria

A group of bacteria found primarily in the intestinal tract of humans and animals, as well as in their feces. Therefore, these bacteria are used as an indicator of the presence of pathogenic contaminants in the water, the most common being Escherichia Coli. Which can be removed with chlorine, ultraviolet light or ozone.

Iron bacteria

Organisms capable of using iron oxide (either from water or from a steel pipe) in their metabolic process precipitate gelatinous ferric hydroxide compounds. These organisms tend to accumulate in pipes and tanks during periods of low flow, dislodging them causing staining, taste and odor problems. They are not harmful to human,


Any substance or agent that kills bacteria or inactivates your reproductive system. Non-bacterial spores and microorganisms (algae, fungi, and viruses) are not necessarily killed with bactericides.


The ability to inhibit the growth of bacteria without destroying them. For example, activated carbon impregnated with silver, prevents bacterial colonization in the container that contains it, but does not eliminate them.


Pressure unit. One bar equals 14.5 pounds per square inch (psi) or about 0.987 standard atmospheres.


An alkali that releases hydroxyl ions when dissolved in water. Bases react with acids to form a neutral salt and water.


A chemical that can kill or inhibit the growth of organisms such as bacteria, fungi, molds, etc. Biocides can be harmful to humans. Biocides are also capable of eliminating spores from living organisms, these are known as sterilizing agents.


Substances subject to degradation into simpler substances by biological action. Some examples are the degradation of detergents, sewage and organic matter by bacteria.


The accumulation of microbial growth embedded in an adhesive film that is fixed on the surface of materials, such as the inside of pipes and storage tanks. Disinfectants and sanitizers may have no effect on the bacteria that are protected within the film.


A chemical that does stabilize pH values in solutions.


Upper valve for a filter or softener whose purpose is to pass raw water through the bed for its treatment, as well as to allow backwashing and / or regeneration of a softener. It has inlet, outlet, drainage and brine injection connections (in the case of a softener).

Pressure drop

A decrease in the pressure of the water during its flow due to internal friction between the water molecules, friction due to its passage along the pipe and its accessories, and due to changes in direction.

Calcium (Ca)

One of the most abundant elements in the earth’s crust. It is also one of the two main constituents of hardness in water. Contributes to the formation of whitish encrustations on surfaces that are in contact with hard water.


Calcium carbonate (CaCO3). A trade name for finely ground limestone, very high in calcium carbonate, which can be used to increase the pH of an acidic water.

Bed or bed

Name used in filtration to name the material contained within a column designed to filter, adsorb, precipitate or exchange ions.

Support bed

A layer of gravel with the appropriate granulometry to facilitate the uniform distribution and collection of the water and the backwash flow. It is placed at the bottom of a tank, as a support for the granular medium.

Bed Expansion

The desired effect during the backwash: the particles of the granular medium are decompressed and rise in the column, the objective is to wash all the sediment trapped in the bed through the backwash flow. The proper flow to expand the bed depends on the grain size of the medium, its density and the temperature of the water.

Bed Depth

The height of the filter media bed in the column, after its compaction, generally expressed in inches. The height is related to the adequate contact time to allow adequate filtration or adsorption in the granular medium.

Empty bed (Freeboard)

Height above bed of granular medium available for bed expansion during backwash. It can be expressed as a linear distance in inches or a percentage of the depth.


Phenomenon produced in a bed of granular medium, in which the water or regenerant form channels through the bed of less hydraulic resistance. Channeling may be due to bed fouling, poor distribution design, low operating flow rates, or insufficient backwash (poor bed expansion).


The property of a medium to adsorb or precipitate a specific contaminant can also refer to the property of a resin to exchange ions. The capacity is accompanied by the specific conditions and is expressed in mass of the contaminant / volume of the granular medium.

Activated carbon

Activated carbon or activated carbon is porous carbon that traps compounds, mainly organic, present in a gas or in a liquid. It does so with such effectiveness that it is the most widely used purifier by humans. In water treatment it is commonly used to dechlorinate, reduce the concentration of organic compounds. It is marketed in the form of granules, powder or pellets.

Bone charcoal

A black substance with a carbon content of approximately 10%, produced by charring animal bones. It is used as a selective anion exchanger for the reduction of fluorides and arsenic in water.


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Total organic carbon (TOC)

The measurement of carbon dioxide produced from organic compounds when a water sample is atomized into a combustion chamber. The amount of carbon covalently bound to form organic compounds in a water sample.


A substance that produces or favors the appearance of cancer.

Positive charge

The electric potential acquired by an atom that has given up one or more electrons; characteristic of a cation.

Filter cartridge

Compact and easily removable filter element. They are manufactured in various materials that provide specific properties such as retention of particles of a certain size, chemical resistance, resistance to high temperatures, etc.


A positively charged ion.


A complete course of ion exchange operation. For example, a complete cation exchange cycle would involve: regeneration of the resin, rinsing to remove excess regenerant, depletion, backwashing, and finally regeneration again.

Cycle of concentration

Concentration ratio.

Hydrogen cycle

A complete course of cation exchange operation in which the cationic medium is regenerated with acid and all cations in the water are removed by exchange with hydrogen ions.

Hydrological cycle

The natural water cycle, which includes the precipitation of water from the atmosphere such as rain or snow, the flow of water on or through the earth, and the evaporation or transpiration of water vapor in the atmosphere.


The study of the relationships between temperature, transport and the velocity of very small particles. It is used to describe the speed of physicochemical reactions that occur in a granular medium.

Hydraulic Classification

The rearrangement of the granular medium particles in a column. As the backwash water flows up through the bed, the particles are placed in a mobile condition where the largest particles remain at the bottom and the smallest particles rise to the top of the bed .


A mechanical device specifically designed to feed chlorine, either in gaseous, liquid or solid form, depending on its design, to a water supply, there are manual or automatic devices and for continuous or block operation.


Chloramines are a type of organic amines that are produced when ammonia and chlorine (in the form of hypochlorous acid) react with each other. It does not form trihalomethanes.


Widely used in water disinfection and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas (chlorine gas), as a liquid (sodium hypochlorite), or as a solid (calcium hypochlorite). In water, chlorine reacts with organic compounds to form trihalomethanes (THMs) that can cause cancer, however these compounds are perfectly adsorbable by activated carbon.

Combined Chlorine

It is the already inactive chlorine that is combined with organic matter, is toxic at certain levels, produces irritation and some combinations can be carcinogenic.

Residual free chlorine

This form of chlorine has the greatest disinfecting and oxidizing power, it corresponds fundamentally to the presence of hypochlorous acid and hypochlorite ion.

Total chlorine

The total chlorine concentration is a solution, which includes the combined chlorine and the residual free chlorine.


It is a metal salt or polymer that can be cationic (positively charged), anionic (negatively charged), or non-ionic (neutrally charged).

In water treatment, it is used to remove pollutants, facilitate their precipitation, in case their subsequent flocculation is necessary and their elimination by flotation, filtration or decantation.


Very finely divided solid particles larger than molecules but small enough that they do not settle in solution; intermediate between a dissolved particle and a suspended solid. Typically between 0.1 and 0.001 microns in diameter, it generally requires coagulation prior to filtration.

Volatile Organic Compounds (VOC)

Organic compounds that vaporize at relatively low temperatures.


It is the proportion or relationship between the amount of solute and the amount of solution. It is expressed in units of mass over volume.

Heat conduction

Heat transfer process based on direct contact between bodies, without material exchange.


Characteristic that allows to transport an electric current. In water, conductivity is related to the concentration of dissolved salts, which form ions capable of carrying electrical current. The unit of measurement is the mho.


The presence in the water of any physical, chemical, biological or radiological substance that is different from the formula of water (H2O).


It is the transport of heat through the movement of a fluid.


The destructive disintegration of metals by electrochemical means. Corrosion of iron and steel is commonly called rust.


The removal of excess free chlorine from the water. The complete or partial reduction of free chlorine by any chemical or physical process.


The process of removing color from bodies of water such as tannins or humic acids from water through oxidation, coagulation / flocculation, adsorption or ion exchange.

Delta P

The pressure drop or loss in a pressurized system is due to: the speed and turbulence of the water that flows through it, the restrictions it encounters and the roughness of the surfaces through which the water flows.

Chlorine demand

A measure of the amount of chlorine that will be consumed by organic matter and other oxidizable substances in a water before residual chlorine is found in the water. The chlorine demand represents the difference between the total chlorine feed and the residual chlorine.

Biochemical oxygen demand (BOD)

Abbreviation for Biochemical Oxygen Demand. The amount of oxygen required for the oxidation of organic matter by biological action under standard test conditions. It is widely used as a measure of wastewater and wastewater pollution.

Chemical oxygen demand (COD)

An indirect measure of the amount of oxygen used by organic and inorganic matter in water. This is measured by means of a laboratory test with the use of a chemical oxidant, therefore, it does not necessarily correlate with the biochemical oxygen demand.

Density, apparent (density, bulk)

The ratio of mass per unit volume under specific conditions, including pore volume and void spaces between particles.

Real density

The ratio of mass per unit volume under specified conditions, excluding pore volume and void spaces between particles.


Process for reducing alkalinity in a water supply. It is generally achieved through cation and anion exchange systems.


Process of removing salt from seawater or brackish waters, to make them drinkable or useful for other purposes.


The removal of dissolved gases from water, such as carbon dioxide, methane, hydrogen sulfide, and oxygen. This can be done by subjecting the water to a pressure below atmospheric (vacuum degassing) or by passing air through the water at atmospheric pressure (air extraction).

Middle wear

The process in which solids wear away by friction, often between particles of the same material. Filter media and ion exchange materials are subject to wear during backwash, regeneration, and service.


A water treatment that inactivates, destroys or reduces pathogenic bacteria, viruses and other microorganisms in order to obtain microbiologically safe water for human consumption. An effective disinfection should reduce the population of microorganisms in a range of 99.9 to 99.9999 %.


The reduction of dissolved minerals and salts (both organic and inorganic) from a solution using a two-phase ion exchange process. First, the positively charged ions are exchanged by a cation resin for an equivalent amount of hydrogen ions. The negatively charged ions are then exchanged by an anionic resin for an equivalent amount of hydroxide ions. Hydrogen and hydroxide ions introduced in this process join together to form water molecules. This process is also known as demineralization.


The reduction of dissolved inorganic solids (salts) from a solution. Typically achieved by reverse osmosis, distillation, or electrodialysis.


Usually refers to synthetic detergent, but can be any cleaning material, such as soap, alkaline materials, synthetic detergents, solvents, and abrasives. Synthetic detergents are known as lathering and soap-like surfactants, but they are not made from fatty acids and bleach.


The separation of components of a solution by diffusion through a semi-permeable membrane capable of allowing the passage of certain ions or molecules while rejecting others.

Carbon Dioxide

Gas found in nature (CO2) present in the atmosphere caused by the oxidation of organic matter. Carbon dioxide dissolves in water as carbonic acid (H2CO3).

Manganese dioxide

An insoluble brown or dark gray compound found in nature as pyrolusite, it is used as a catalyst agent in oxidation and precipitation reactions of iron, manganese and / or hydrogen sulfide.


Chemical that is added to water in order to keep the particles in suspension.


A calcium magnesium carbonate mineral found in nature in extensive beds of compact limestone and marble rich in magnesium carbonate.


Parallel hydraulic arrangement. It can be applied for filtration, softening, adsorption equipment, etc. It is used when the filters do not have the full capacity to treat the required flow.


A characteristic of natural water due to the presence of dissolved calcium and magnesium. The hardness of the water is responsible for the formation of scale in pipes, water heaters, and prevents the formation of foam when reacting with soaps. Hardness is generally expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent.

Total hardness

The total of all divalent metal cations, primarily calcium and magnesium hardness, expressed in terms of calcium carbonate equivalents.


A venturi with an opening in the throat that is used to draw in (draw in) air or liquid. The common method of introducing brine into a water softener, or the typical way that ozone is injected into a line continuously.


The outlet of a water treatment system.


It is a combination of electrodialysis and ion exchange. Its function is to remove ions from the water. The technology consists of a combination of ionic exchange resins, both cationic and anionic, ion-selective membranes, an anode, a cathode and the cyclical application of an electrical potential, which allows obtaining deionized water with a high degree of purity.

It is also known as EDI.


Procedure for separating ions from a solution in the presence of a magnetic field using ion-selective membranes.


A chemical compound that dissociates or ionizes in water to produce a solution that will conduct an electrical current. It could be an acid, base, or salt.

Crosslinking a resin (Decrosslinkage)

The degradation of an ion exchange resin structure by destruction of the crosslinking polymer as a result of aggressive attack by chlorine, ozone, hydrogen peroxide, or heat. Crosslinking causes higher moisture content in an ion exchange resin and physical swelling of the beads.

Chemical stability

Resistance to chemical change that materials must have despite contact with aggressive solutions.


The aging process of a body of water caused by the depletion of available oxygen. It can be accelerated by human activities that add too many nutrients to the water, such as runoff from barns or fertilizers.


Process in which a substance changes its physical state from liquid to gaseous.


An acid-base indicator that does not produce color in an acidic solution (pH <8.2) but turns pink or red in an alkaline solution (pH> 8.2).


Natural mineral with a MnO2 content between 75 to 85%, it works as a catalytic medium in the precipitation of iron and manganese. It may require the use of oxidants when the ORP value is less than 170 mV.


The process of passing water through a porous material to retain suspended solids. There are various application technologies, such as granular media contained in tanks or columns, filter cartridges, cellulose plates, mesh filters, etc.

Absolute filtration

Filtration range specification. Filter classification means that 99.9% (or essentially all) of the particles larger than the micron specification will be retained by the cartridge.

Nominal filtration

Filtration range specification. Indicates the particle size that a filter retains in a greater percentage, the percentage is measured by weight and can vary according to the criteria of each manufacturer.


Organic or inorganic chemicals used to agglomerate the small particles formed by a coagulant into large flocs that allow them to be filtered or decanted. There are emulsion or powder presentations.

Flow (Flow)

The amount of fluid that circulates through a section of the pipeline (pipe, pipe, oil pipeline, river, canal, …), per unit of time.

Design flow

The operating flow plus a security percentage between 10 and 15%.

Operation flow

Actual flow that is fed into a treatment system.

Parallel flow

An arrangement of pipes that directs separate streams through two or more water treatment units in a balanced manner, providing an equal flow to each device. The inlets of two or more units are connected to each other and the outlets are connected to each other so that water will flow through the units simultaneously.

Serial flow

A piping arrangement in which all the operating flow is fed to a first unit of the treatment system, and the effluent is fed to a second unit, and so on.

Instant flow

Flow measured at a given time.


Granular Activated Carbon acronym in English Granular Activated Carbon.


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

Giardia lamblia

A common protozoan found in water and derived from animal droppings. It can cause a contagious water-borne illness characterized by acute diarrhea. It is resistant to disinfectants such as chlorine, iodine or ultraviolet light. Giardia can be removed with four micron filters.

Water hammer

The shock wave produced by the sudden change in the flow of water through a pipe system. Water hammer produces an instantaneous increase in normal system pressure. Installing a water hammer arrester will absorb these shock waves.

Gallons per day (gpd)

Unit that expresses a flow (unit of volume / unit of time).

Gallons per minute (gpm)

Unit that expresses a flow (unit of volume / unit of time).

Gram (g)

A measure of mass, symbol g, which is equal to one thousandth of a kilogram.

Grain (gr)

A unit of weight equal to 1/7000 of a pound or 0.0648 grams.

Grains per gallon (gpg)

An expression of concentration. One grain per gallon is equivalent to 17.1 g / ml. Commonly used to express total hardness concentration in water.


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

Sodium hexametaphosphate

Chemical added to water to increase the solubility of certain ions and inhibit their precipitation. Known as a sequestering agent, it forms a thin film that protects metals from corrosion.

Sodium hydrosulfite

A strong reducing agent used as the main ingredient in various resin cleaners used to clean contaminated iron in ion exchange resin beds.


The term used to describe the anionic hydroxide radical (OH-) that raises the pH in a solution.


An element that is often found dissolved in groundwater (in the form of ferrous iron) in concentrations that generally range from zero to 10 ppm (mg / l). Its presence in water causes staining due to its oxidation and precipitation (as ferric hydroxide), due to unsightly flavors and colors.

Ferric iron

Small solid iron particles containing trivalent iron (Fe + 3), usually as gelatinous ferric hydroxide or ferric oxide (Fe2O3), which are suspended in water. Ferrous iron (soluble iron) is easily converted to ferric iron by exposure to oxygen found in both water and air. Ferric iron can be removed by filtration, but not by ion exchange.

Ferrous iron

Divalent iron (Fe + 2), which is soluble in water.

Organic iron

Organically bound iron that can give water a pinkish hue. It is found only in groundwater supplies and cannot be removed by filtration. Like soluble iron, organic iron stains surfaces rusty or orange.


Also called filter holder or cartridge holder. It is a container of some specific material that contains a bag filter as well as one or more cartridge-type filters.


Precipitate that forms on the surfaces is in contact with water, it is the result of the supersaturation of one or more salts present in the water.

Soiling Index (SDI)

Measurement of the tendency of water to dirty a membrane due to contamination by colloidal particles. An SDI less than or equal to 5 is acceptable.

Langelier index

Parameter that allows knowing the quality of the water. Provides information on the fouling or oxidizing character of the water. It is based on balances of bicarbonate, carbonates, pH, temperature, calcium concentration and the salinity of the water.


Chemical that interferes with a corrosion or precipitation reaction.

Ion exchange

Reversible chemical process in which unwanted dissolved ions are exchanged for other ions with a similar charge. The direction of the exchange depends on the affinities of the exchanger for the ions and their concentration in the solution.


An atom, or group of atoms in a solution that functions 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.


Physicochemical phenomenon by which molecules are dissociated into ions, simpler electrically charged particles.

Adsorption isotherm

Graph that describes the equilibrium of the adsorption of a material on a surface at constant temperature.

Deep bed (Filtration)

Filtration process in which water progressively flows between the spaces and pores of a granular medium. Deep bed filters are designed to trap particles deep in the medium. This filtration mechanism can be found in multimedia filters and in spun and foamed cartridge filters.


It is a family of more than 26 species of bacteria, such as Legionella pneumophila, which is the cause of a disease similar to pneumonia. These bacteria are known to breed around 30 ° C and are commonly found in humidifiers, cooling towers, and bathtubs. The route of infection is inhalation.

Drain line

A pipeline or conduit from a water conditioning unit used to transport backwash water, regeneration waste, and / or rinse water to a drainage or waste system.

Ultraviolet light

A type of radiation (light) with a wavelength less than 3900 angstroms and greater than 100 angstroms. Ultraviolet light is used as a disinfectant in water treatment.


One of the elements that make up the earth’s crust. Magnesium and calcium are elements that cause hardness in water.

Quartz sleeve

Also called a quartz jacket. It is a high purity quartz tube used to protect the high intensity lamp from ultraviolet equipment. Usually this retards less than 10% of the UV radiation dose.

Manganese (Mn)

An element that is sometimes found dissolved in groundwater, usually with dissolved iron but in lower concentrations. Causes black stains on clothing and plumbing at concentrations above 0.05 mg / l.

Pressure gauge

Instrument to measure the pressure of fluids.

Inorganic material

Matter that is not derived from living organisms and does not contain organically produced carbon.


A thin sheet or surface, natural or synthetic, with a microporous structure that filters particles of small sizes in the order of ions and molecules. These membranes are known as semi-permeable because they allow the passage of some substances and restrict the passage of others. The membranes are used to manufacture reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and absolute cartridge filters.

Microgram per liter

Also known as parts per billion (ppb). The common symbol for micrograms per liter is µg / L.


One millionth of an ohm. A unit of measurement used to test the electrical resistance of water to determine its purity. The purer the water, the greater its resistance to conducting an electric current. Absolutely pure water has a resistance of eighteen million ohms in one centimeter at a temperature of twenty-five degrees centigrade.


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

Microsiemens / cm

Microsiemens are a practical unit for measuring conductivity and indicate an approximate unit for the concentration of solids in water. A water with a concentration of 100 mg / l of sodium chloride has a resistance of 4.716 ohms / centimeter and a conductivity of 212 microsiemens per centimeter. A totally “pure” water from a mineral point of view, has a conductivity of 0.03 microsiemens per centimeter at a temperature of 25 ° C. This measurement is also known as a micromho.

Milligram per liter

It is a measure of the concentration of a dissolved substance. A concentration of one mg / l means that one milligram of substance is dissolved in one liter of water.


Term applied to inorganic substances, such as rocks and similar matter found in the strata of the earth. Minerals normally have a defined chemical composition and crystal structure. The term also applies to matter derived from minerals, such as inorganic ions that are found dissolved in water.


Unit of quantity of matter of the International System, symbol mole.


The smallest particle of an element or compound that retains its characteristics. A molecule is made up of one or more atoms.


It is the process by which a fluid is passed through a semi-permeable membrane at a certain pressure, so that a separation occurs based on the size of the molecules that can cross said membrane (between 0.001 and 0.01 mm).

Two streams of the inlet fluid are obtained: the permeate, a fluid that has passed through the membrane, and the concentrate, a fluid that has not crossed the membrane and which concentrates the components of the main stream that cannot cross the membrane.

NSF International

Independent organization with the mission of protecting and improving human health worldwide. The NSF mark assures consumers, retailers and regulators that products have been rigorously tested and meet the requirements of all standards.


From the English Nephelometric Turbidity Unit, it is a unit used to measure the turbidity of a liquid.

Iodine number

It corresponds to the milligrams of iodine that a gram of carbon adsorbs (on a dry basis), when the residual concentration of iodine in the solution is 0.02N.

In certain types of carbons that are activated under certain conditions, the iodine number has been shown to be relatively proportional to the surface area of the carbon (area that is determined by nitrogen adsorption).


It is the standard unit that measures the resistance to the passage of electric current. One ohm is equal to the resistance between two points on a conductor when a potential difference of one volt creates an electric current of one ampere.

Batch operation

A method in which a fixed amount of water is treated in a single step or operation.


Any substance from plants or animals and is characterized by its molecular structure of carbon-carbon and carbon-hydrogen bonds. Some examples are hydrocarbons, wood, sugars, proteins, methane, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM), and trichlorethylene (TCE).

Anaerobic organism

An organism that can thrive in the absence of oxygen (air), like bacteria in a septic tank.


A process of diffusion of a solvent such as water through a semi-permeable membrane that allows the passage of the solvent but prevents the passage of the dissolved species. The normal meaning of solvent is from dilute solution to more concentrated solution. Osmosis makes the most concentrated solution dilute, this process tends to equalize the concentration on both sides of the membrane.

Reverse osmosis

A water treatment process that is used to reduce the concentration of dissolved material in the water, using pressure as a driving force through a semi-permeable membrane that forces the passage of water in the opposite direction to the natural process of osmosis.


A chemical process in which a molecule, ion or atom gives electrons to an oxidant and the oxidant is reduced. Oxidation never occurs alone, but always as part of the oxidation-reduction (redox) reaction. Combustion is an extremely fast form oxidation.

Ferric oxide

A reddish corrosion product sometimes found in water. Rust forms as a result of the electrochemical interaction between iron and oxygen in the presence of moisture.

Ozone (O3)

Molecule composed of three oxygen atoms, is formed when the two atoms that make up oxygen gas dissociate.

It is a strong oxidizing agent that is unstable in the environment, therefore it must be generated on site. One of the most effective disinfectants.

Parts per billion (ppb)

Concentration unit, indicates the number of parts by weight of a dissolved or suspended component, per billion parts by weight of water.

It is of relatively frequent use in the measurement of the concentration of very dilute chemical compounds, as well as of substances that are at the trace level.

Parts per million (ppm)

Unit of concentration, indicates the number of parts by weight of a dissolved or suspended component, per million parts by weight of water.


The smallest piece of matter that maintains the chemical properties of a body.

pH (potential of hydrogen)

It is a measure of acidity or alkalinity of a solution. PH indicates the concentration of hydrogen ions present in a solution.


A gap between the particles or molecules that make up a body.

Potential Z

The electric potential that exists across the interface of all solids and liquids. This potential represents the difference in voltage between the surface of the layer that surrounds a colloid and the liquid around it.

Hydrostatic pressure

A measure of structural strength and the ability to maintain water pressure.

Operating pressure

The pressure range, generally expressed in pounds per square inch, over which a water conditioning device or water system is designed to operate.

Osmotic pressure

The pressure that must be applied to a solution to stop the net flow of solvent through a semipermeable membrane.

Minimum bed depth

The minimum height that the bed contained in a column must have, whether of a granular medium, adsorbent or for ion exchange. This is usually the length of the mass transfer zone.


A natural vitreous aluminum silicate mineral from volcanic ash that is used as a water treatment filtration medium.

Point of entry (POE)

A water treatment device that is installed at the main entrance of a building and acts as a centralized treatment.

Point of use (POU)

A water treatment system designed to connect at the actual point of water use.


In a recirculating system, it is the discharge of water with a high content of dissolved solids, for its subsequent replacement of the level with replacement water, the intention is to reduce the concentration of TDS and avoid the formation of precipitation.


Physicochemical treatment that seeks to eliminate undesirable organic and inorganic pollutants in the water.


The abbreviation of English for reverse osmosis RO “reverse osmosis”.


Natural radioactive element (radius 226 and radius 228) originated by the decay of uranium and thorium. It can be removed from water through cation exchange.


Colorless and odorless radioactive gas of short life which occurs in nature through the decay of the uranium / radium series, this is soluble in water. Radon is a carcinogenic element to humans. The method of removing radon from water is by means of aeration or activated carbon.


Oxidation processes to restore the adsorption properties of a spent adsorbent, such as activated carbon.


It is the ability of the membrane to reject the passage of dissolved solids and other contaminants into the water of the product.


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


It is the use of a regenerant to displace contaminating ions in an ion exchange resin bed during service and they are replaced with the necessary ions to restore the exchange capacity of the medium for reuse. This process is also known as media rejuvenation and is similarly used in catalytic media.


It is a chemical solution (regenerant) used to restore a depleted ion exchange resin bed. The use of regenerants also takes place to restore catalytic media (iron and manganese removal filters).


The amount of a specific material that remains in the water after a treatment process. It can refer to an unwanted material resulting from incomplete removal, such as a hardness leak, or a substance intended to remain in the treated water, such as residual chlorine.

Strong Base Anion Exchange Resin (SBA)

Strong base anion exchange resins typically have a quaternary amino group as a fixed positive charge. Strong base anion resins readily yield a hydroxide ion if the pH value is less than 13. SBA resins are less stable than SACs and are characterized by the fishy odor of amino groups, even at room temperature.

Weak Acid Cation Exchange Resin (WAC)

In WAC exchange resins, the functional group of the resin is usually a carboxylate. Weak acid cation resins have pKa values in the range of 4.5 to 5, therefore they do not readily yield a proton, unless the pH is higher than 6. Weak acid resins often require alkaline species in water to react with the more closely bonded hydrogen ions.

Strong Acid Cation Exchange Resin (SAC)

In SAC exchange resins, a charged sulfate group often acts as the exchange site. The term strong in SAC represents the ionic strength with which the polymeric network attracts ions from contaminants, this represents the ease with which the functional group loses a proton.

Weak Base Anion Exchange Resin (WBA)

In weak base exchange resins, the exchange site is generally a tertiary amino group that does not have a permanent fixed positive charge. Weak base anion exchange resins are available in other chloride or free base forms. The effective operating range of these resins is pH <6.

Ion exchange resin

They are generally cross-linked geometric polymer resins containing functional groups covalently bonded with fixed ionic charges; This structure forms a network of ionic bonds, which are responsible for electronically attracting pollutants. There are two main types of resins: macroreticular and gel resins.

Macroporous resin

Special ion exchange resins designed with wider pores than conventional resins and greater resistance to oxidation and clogging by organic contaminants. These were developed to have a wide surface area for reactions with high molecular weight organic matter.


The upward or countercurrent flow of water through a filter or ion exchange medium consists of lifting the medium and sending the foreign matter particles to the drain.


* (1) Commonly crystalline ionic chemical compound product of an acid-base reaction.

* (2) The common name for the specific chemical compound sodium chloride (NaCl), used in the regeneration of ion exchange water softeners. In chemistry, the term applies to a class of chemical compounds that can be formed by neutralizing an acid with a base.


* Water solution saturated with sodium chloride

Solubility of sodium chloride in water: 359 g / l


Sanitation is the process of reducing the microbial content, up to a certain level of safety, without the complete disappearance of pathogenic microorganisms but without causing any type of infection.


It is a chemical compound that can associate with metal ions to form stable organic complexes so that they remain soluble without creating scale.


Sediments are solid matter, in the form of particles or grains, found on a surface.

Activated silica

A colloidal substance that is used as an adjuvant or an aid in the flocculation or coagulation of a water system.


Crystalline silica is a mineral compound found abundantly in rocks, soil, and sand, made up of one silicon atom and two oxygen atoms (SiO2)


Salt formed by a combination of silicic acid and a base, which can be obtained by joint fusion of silica with an alkali metal carbonate; It is used in the manufacture of glass and in construction and refractory materials.

Alternate system

As in pressure in the sewer system or creating negative pressure in the water supply line. Local plumbing codes generally require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.

Exchange sites

Locations on ion exchange resin beads that contain mobile ions that are available for exchange with other ions in a solution that passes through the bed. These sites are also called functional groups.


The slug is the unit of mass in the Gaussian system which is a system of units based on the centimeter, the gram and the second.


Sodium is a chemical element with the symbol Na with atomic number 11. It is a soft, unctuous, silver-colored alkali metal, very abundant in nature, found in sea salt and the mineral halite.

Total dissolved solids (TDS)

It is the soluble material made up of inorganic and organic matter that remains as a residue after evaporating and drying a sample previously filtered through a fiberglass filter with a pore of 1.5 µm at a temperature of 105 ° C.

Total Suspended Solids (SST)

It is the material constituted by the sedimentable solids, the suspended solids and colloidal that are retained by a fiberglass filter with pore of 1.5 µm dried and brought to constant mass at a temperature of 105 ° C

Total solids (ST)

It is the residue that remains in a capsule after evaporating and drying a water sample at a temperature of 105 ° C-

Total volatile solids (STV)

Amount of organic and inorganic matter that volatilizes due to the effect of calcination at 550 ° C.

Saturated solution

A solution that contains the maximum amount of solute that it can dissolve at this temperature.


A solvent is a chemical substance capable of diluting a solute (a chemical substance that is found in less quantity and dissolves in the mixture).


Chemical substance that is dissolved in a solution or mixture.

Caustic soda

Common name for sodium hydroxide. It is a chemical compound with strong base properties. It is mainly used as a strong alkalinizer in water, in the saponification process and in regenerations of OH- based anionic resins.

Water softener

A water softener (or water softener) that is equipped with a timer, meter, or sensor that automatically starts the backwash and / or regeneration process at preset time intervals. A predetermined number of gallons of water use or as determined by a sensor. All operations, including bypassing treated or untreated water (depending on design), backwashing, brine, rinsing, and returning the unit to service are performed automatically.

Twin softener

Type of hydraulic arrangement in a softening system, to obtain softened water regardless of which one of the equipment is regenerating.

The arrangement consists of alternating the total water flow of a unit, and by means of a motorized valve, being able to alternate when the softener has regeneration in turn.

Hydrogen Sulfide (H2S)

A corrosive and flammable gas produced from decomposing organic matter, commonly known as “sulfur.”


Cellulose triacetate. It is used to make reverse osmosis membranes.


Organic phenolic compounds that are produced by the metabolism of trees and plants. They are formed during the decomposition of vegetation. Tannins impart a slightly yellow color to the water. These molecules tend to form anions in water when the pH is higher than 6 and can be treated by means of anion exchange resins. When the pH is less than 5, it is better to treat the tannins with activated charcoal.

Brine tank

A tank that is located next to the softening unit and acts as a salt storage for the supply of brine to the system.

TCE (trichlorethylene)

A toxic volatile organic substance, typically used as an industrial solvent.


The abbreviation for “total dissolved solids” SDT. It is the total weight of the solids that are dissolved in the water. The TDS are determined by filtering a known volume of water (usually through a 0.45 micron membrane), subsequently the water is evaporated at a defined temperature (103 ° -105 ° C), and the residue is weighed.

Contact time.

The actual time during which water remains in contact with an oxidant, regenerant, or water conditioning medium within a treatment system. The amount of contact time determines the effectiveness of the system.

Primary treatment

Stage in which fats, oils, coarse solids present in the waste water are removed. Physical-chemical processes such as sedimentation, flotation, coagulation – flocculation and filtration can be used.

Secondary treatment

The second step in wastewater treatment is the biological one to remove suspended and dissolved solids and biochemical oxygen (BOD) after initial primary treatment.

Tertiary treatment

The third stage in wastewater treatment consists of reducing pollutants through chemical disinfection, microfiltration, and activated carbon.

Trihalomethanes (THM)

A group of organic chemicals, suspected of being carcinogenic, these substances are formed when chlorinated products are used for disinfection in natural waters with a high content of organic matter such as humic acids. Chloroform is one of the most common substances generated by the reactions of chlorine with humic acids.


A measure of the amount of suspended matter in water, this matter causes the scattering and absorption of light rays, giving the water an opaque appearance. Turbidity is generally reported in Nephelometric Turbidity Units (NTU) and is determined by light scattering measurements. NTUs should not exceed 0.5 in drinking water. Turbidity can protect bacteria from sterilization.


It is a cross-flow filtration method (similar to reverse osmosis but low pressure) that uses a membrane to remove small colloids and large molecules from water or other liquids. Ultrafiltration removes particles in a size range between 0.002 and 0.1 microns, and rejects organics with a molecular weight greater than 1000 daltons, allowing smaller ions and organics to pass through.

Jackson Turbidity Unit (JTU)

An arbitrary unit of turbidity originally based on a suspension of a specific type of silica with the turbidity measured on a Jackson Candle turbidimeter. This has been replaced by the nephelometric turbidity unit (NTU).

Nephelometric Turbidity Unit (NTU)

The standard unit of measure used to measure turbidity in water. It uses a light scattering effect of fine particles suspended in a beam of light. The NTU has replaced the Jackson Turbidity Unit (JTU) as the measurement standard.


A radioactive metallic element that occurs naturally in combination with other materials. Uranium 238 is the most common form. Uranium in natural waters exists in the form of anionic complexes UO2(CO3)22- and UO2(CO3)34-.

Check valve

They are valves designed to prevent fluid from returning to a line. When the flow becomes positive through the line, this valve closes instantly. They are also called non-return valves. It is unidirectional and must be placed in the correct direction to perform its function.

Relief valve

Valves designed to relieve pressure when a fluid exceeds a pre-set limit (set pressure). Its mission is to prevent the explosion of the protected system or the failure of equipment or pipes due to excess pressure. There are also valves that relieve the pressure of a fluid when the temperature (and therefore the pressure) exceeds a limit set by the manufacturer.

Air release valve

It is a device to eliminate gases in liquids, it is designed so that a pumping system works at the maximum calculated flow capacity. It has a vent hole that automatically purges the accumulated air, it is located in the high points when the system is in operation and under pressure.


A tube with a tapered throat that causes an increase in velocity, therefore a decrease in the pressure of the fluid passing through it. It is the common element used to educt or aspirate a regenerant in a water softening system.


The tendency of a substance to go into the vapor phase at certain conditions of pressure and temperature.


Cross-linked polyethylene.


Natural or synthetic hydrated sodium alumina silicate with ion exchange properties. Zeolites have been largely replaced by synthetic cation ion exchange resins. Modified zeolites such as manganese greensand and synthetic manganese zeolites continue to be used as catalysts in filters to retain iron, hydrogen sulfide, and manganese.

Mass Transfer Zone (MTZ)

The MTZ represents the length of the bed necessary for the adsorbate to be transferred from the fluid to the adsorbent. All adsorbable contaminant is retained in the MTZ, so the medium below the MTZ remains unexposed to the contaminant. As the height of the MTZ is saturated, it moves through the bed and finally the non-adsorbed solutes begin to be detected in the effluent, this is known as the breaking point at which the medium must be replaced or regenerated.

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