Water Dictionary

Understanding water terms

Activated Carbon

GAC, Carbon, Activated Coal, Charcoal, Activated Charcoal

A widely used water filtration medium commonly used for dechlorination, organics removal and other specialty processes. Base products include but not limited to bituminous coal, coconut and lignite.


Dealkalizer, Alkaline Water, M-Alkalinity, P-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.

Anion Resin

White stuff, SBA, Strong Base Anion, WBA, Weak Base Anion, Tannin Resin, Type 1 Anion, Type II Anion, Organic Scavenger Resin

An ion with a negative charge. Anion Exchange is an ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger.


Resin Bed, Filter Bed, Softener Bed, Softener Bed

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


Salt Solution, Saturated Brine, Saline

A strong solutions of salt(s), usually sodium chloride and other salts too. Potassium or sodium chloride brine is used in the regeneration state of cation and or anion exchange water treatment equipment. Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCI by weight at 60° F.

Brine Tank

Trash Can, Salt Bale, Brine Keeper, Salt Tank, Brine Maker, Brine Holding Tank, Brine Measuring Tank

A brine tank holds the brine solution used in conjunction with water treatment equipment. The brine is used to regenerate the resin.

Calcium Scale

Calcium is one of the principal elements making up the earth’s crust. Calcium compounds, 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.


Accelerator, Catalytic

A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.

Catalyst Media

Catalytic Conversion Filters, Chloramine Filter

Those filter media which can cause certain reactions to occur in water treatment, such as activated carbon, calcite, manganese greensand, manganese oxides, and dissimilar metal alloys.

Cation Resin

SAC, Strong Acid Cation, Softener Resin, WAC, Wek Acid Cation, Zeolite, Softener Beads, Softener Beads, Softener Resin

An ion with a positive charge. Cation Exchange is an ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger.


Alkalinity Removal, Dealkalization

The removal of alkalinity ions from a solution. A dealkalizer contains strong base anion exchange resin that exchanges chloride (the Cl ion of the NaCl) for carbonate, bicarbonate and sulfate. As water passes through the anion resin the carbonate, bicarbonate and sulfate ions are exchanged for chloride ions.


Decationized Water

The exchange of cation for hydrogen ions by a strong acid cation exchanger operated in the hydrogen form.


Degasify, Degassing, Decarbonator, Forced Draft Degasifier, VOC Tower, Air Stripper

The removal of dissolved gasses such as carbon dioxide, methane, hydrogen sulfide, and oxygen by: 1) subjecting the water to a pressure below atmospheric pressure (vacuum degassing) or 2) passing large amounts of air thoroughly through the water at atmospheric pressure (air stripping).


Demineralizer, Demin, 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 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 introduced in this process unite to from water molecules. This process is also called demineralization by ion exchange.


Silica Removal

An ion exchange process designed for reduction of silica from a water supply. Typically a strong base anion exchanger operated in the OH- form is used.

DI Exchange Tanks

PEDI Tanks, Portable Exchange Deionization

Tanks that are leased or rented to a facility lacking the means to regenerate the medium, usually ion exchange resin.

Drinking Water System

Drinking Water Filter, Water Filtration Equipment, Reverse Osmosis System

A drinking water system is the name for collective unit of equipment that purifiesfilters and conditions water used for drinking. Drinking water systems typically utilize multi-step filtration processes.

Effective Size

Mesh Size, Average Size

A measure of the diameter of particles in a media bed or resin bed. Effective size is that mesh size which will permit 10 percent of the bed’s particles to pass and will retain that remaining 90 percent; in other words, that size for which 10 percent of the media grains or particles are smaller and 90 percent are larger.


Boiler Feed Water, Makeup Water, Boiler Make Up Water, Feed Water

The water to be treated that is fed in to a given water treatment system.


Contaminant Reduction

Filtration is the physical process of removing chemical, biological, gaseous or suspended solid contaminants from water through a filter medium.


GPM, Gallons Per Minute, M3/Hr, Feet per Second

The quantity of water or regenerant which passes a given point in a specified unit of time often expressed in US gpm (orL/min). In filter, flow rate is usually measured in gpm/sq. ft of bed area. In ion exchangers, it is expressed in gpm/cu.ft of resin. Flow rate is a critical design parameter by which the effectiveness of the water treatment unit is measured.


Well Water, Ground Water

Water found beneath the surface of the ground. Groundwater is primarily water which has seeped down from the surface by migrating through the interstitial spaces in soils and geologic formation.


Hard Water, Water Hardness

A common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements. The term hardness was originally applied to waters that were hard to wash in, referring to the soap wasting properties of hard water. Hardness prevents soap from lathering by causing the development of an insoluble curdy precipitate in the water; hardness typically causes the buildup of hardness scale (such as seen in cooking pans and in boilers). Dissolved calcium and magnesium salts are primarily responsible for most scaling. Hardness is usually expressed in grains per gallon (or ppm) as calcium carbonate equivalent.

Hydrogen Sulfide

Sulfur, Rotten Egg Smell, Sulphur

A corrosive and flammable gas often found dissolved in well water and often accompanied by iron and low pH values. The odor of water with as little as 0.5 milligrams per liter (mg/L) of hydrogen sulfide concentration is detectable by most people. Concentrations less than one mg/L gives the water a “musty” or “swampy” odor. Over one mg/L hydrogen sulfide concentration gives the water a “rotten egg” odor and makes the water corrosive to plumbing.

Ion Exchange

Water Softening, Demineralization

Ion exchange refers to the process that occurs when a specially charged resin attracts undesirable ions in water, trapping them in the resin bed, and exchanging them for more desirable ions. For example, a water softener uses ion exchange to replace hard water calcium and magnesium ions with sodium ions.

Makeup Water

Boiler Makeup Water, Cooling Tower Makeup Water

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

Mixed Bed

Mixed Bed Resin, Mix Bed

The intermix of two or more filter or ion exchange products in the same vessel during a service run.


Rebed, Resin Replacement, Water Softener Resin Rebed

Complete removal and replacement of the media or resin from a tank is considered a re-bed. Adding to a resin bed that may have lost resin is considered “topping off.”


Regeneration Cycle

The use of a chemical solution (regenerant) to displace the contaminant ions deposited on the ion exchange resin during the service runs and replace them with the kind of ions necessary to restore the capacity of the exchange medium for reuse.


Ion Exchange Resin, Cation Exchange Resin, Anion Resin, Cation Resin

As used in the water processing industry, this term refers to ion exchange resin products which are usually specifically-manufactured organic polymer beads used in softening and other ion exchange processes to remove dissolved salts from water.

Reverse Osmosis

RO, Membrane Filtration

Reverse Osmosis is a water filtration process, where water is forced through a fine porous membrane under high pressure. Impurities in the water are trapped in the microscopic pores of the membrane.

Sulfur Water

Smelly Water, Hydrogen Sulfide Water, Rotten Egg Smell

Sulfur water occurs when high levels of hydrogen sulfide are present in water, giving it a “rotten egg” smell.


Drum, Housing, Container, Reservoir, Canister

That part of a water treatment system that contains the filter medium or ion exchange resin.


Any group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees and plants, and are part of the degradation-resistant fulvic acid materials formed during the decomposition of vegetation.Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.

Total Dissolved Solids

TDS, Dissolved Solids, Dissolved Minerals

Total Dissolved Solids (TDS) refers to the total amount of dissolved minerals, salts, and metals in water. TDS is typically measured in milligrams per liter of water (mg/L) or parts per million (ppm).

UV Light

UV, Ultraviolet Light

Radiation (light) of a wavelength shorter than 3900 angstroms (Å), the wavelengths of visible light, and longer than 100 angstroms, the wavelengths of x-rays. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum. Ultraviolet light is used as a disinfectant.

Water Softener

Water Softening System, Water Conditioner

A water softener uses an ion exchange process to remove the minerals responsible for water hardness, typically calcium and magnesium.

Water Softener Salt

Solar Salt, Softening Salt, Sodium Chloride, Water Softening Pellets

Water softener salt is used to recharge the water softener resin during regeneration, which attracts hard water minerals during the softening process.

Water Softening

The reduction or removal of calcium and magnesium ions, which are the principal cause of hardness in water. The cation exchange resin method is most commonly water treatment. In municipal and industrial water treatment, the process can be lime softening or lime-soda softening.