Glossary of Terms

Glossary of Terms - D

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A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed.
1. A tank used to hold diluted regenerant chemicals prior to being pumped into a batch regeneration of ion exchange beds. Day tanks are commonly used in exchange tank regeneration operations. 2. A tank used to store a chemical solution of known concentration for feed to a chemical feeder. A day tank usually stores sufficient chemical solution to properly treat the water being treated for at least one day. Also called an age tank.
The end of a water main which is not connected to other parts of the distribution system by means of a connecting loop of pipe.
A flow pattern in which all water flows through the medium or membrane (as opposed to cross flow filtration) thus allowing a buildup of a particulate layer on or near the surface of the medium and requiring periodic backwashing, repeated cleaning, or cartridge replacement.
Any process for the reduction of alkalinity in a water supply. Dealkalization is generally accomplished by a chemical feed process or combined cation and anion ion exchange systems.
To draw off the upper layer of liquid (water) after the heavier material (a solid or another liquid) has settled.
The process of drawing off a supernatant liquor without disturbing the underlying lower liquid layers and the precipitate.
The exchange of cations for hydrogen ions by a strong acid cation exchanger operated in the hydrogen form.
The removal of excess chlorine residual, often after super-chlorination. (See Super-Chlorination)
A unit for expressing the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 130 for the average level at which sound causes pain to humans.
The conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.
The alteration of an ion exchange resin structure by destruction of the cross-link polymer (such as divinylbenzene) as the result of very aggressive chemical attack (by chlorine, ozone or hydrogen peroxide, for example) or heat. Decross-linking causes increased moisture content in an ion exchange resin and the physical swelling of the beads.
The removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.
The removal of dissolved gases 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).
As relates to ion exchange, the loss of capacity, reduction of resin particle size, excessive swelling of resin particles, or any combination of these factors resulting in a lessening of the ion exchange capabilities of the resin. This may occur as a result of the type of service for which the resin was used, the solution concentrations used, heat, or aggressive operating conditions.
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 ions introduced in this process unite to form water molecules. The term is often used interchangeably with demineralization.
The finished product water from a public or private utility water plant which is carried through a water main network of pipes and arrives at the point-of-use (homes, institutions, and business facilities).
The pressure drop or loss (in psi) by flowing water in a pressurized system as the result of the velocity and turbulence of the flowing water, restrictions the water flows through, and roughness of surfaces the water flows past. The symbol for Delta P is P. See Also: Osmosis Head Loss Static Head Static Pressure Head Loss
A method of automatically initiating regeneration or recycling in filters, deionizers, or softeners after a pre-determined metered volume of water has been processed. In a softener or deionizer, regeneration may be triggered automatically based upon an electrical or mechanical signal. All operations including bypass (of hard or soft water depending upon design), backwashing, brining, rinsing, and returning the unit to service are initiated and performed automatically in response to the demand for treated water.
The removal of ionized inorganic minerals and salts (not organic materials) from a solution by a two-phase ion exchange procedure; similar to deionization, and the two terms are often used interchangeably.
The biochemical conversion of nitrate and nitrite nitrogen in the soil dissolved in water to gaseous nitrogen.
The mass of a substance per specified unit of volume; for example, pounds per cubic foot. True density is the mass per unit volume excluding pores; apparent density is the mass per unit volume including pores.
See Water Spotting.
A filtration process in which water flows through progressively smaller pore spaces in a filter media bed. Depth filters are designed to entrap particles throughout the mass of filter media, as opposed to a surface filter where only the surface layer does the actual filtering. Depth filtration can be accomplished with a multilayered bed or multimedia filtration.String-wound fiber cartridge elements can also function as depth filters.
Contact between a chemical and the skin.
The removal of dissolved inorganic solids (salts) from a solution such as water to produce a liquid which is free of dissolved salts. Desalination is typically accomplished by distillation, reverse osmosis, or electrodialysis.
[DES-uh-kant] A hygroscopic substance such as activated alumina, calcium chloride, silica gel, or zinc chloride that draws water vapor from the air. Desiccants are used to maintain a dry environment for equipment and materials.
An ion exchange process designed for reduction of silica from a water supply. Typically a strong base anion exchanger operated in OH- form is used.
The opposite of adsorption. The process of removing an adsorbed material from the medium or resin on which it has been adsorbed. Desorption is usually accomplished by heating, a reduction of pressure, by the presence of another more strongly adsorbed substance, or a combination of these means.
A process used to thoroughly dry air; to remove virtually all moisture from air.
A closed container into which heated weighing or drying dishes are placed to cool in a dry environment. The dishes may be empty or they may contain a sample. Desiccators contain a substance, such as anhydrous calcium chloride, which absorbs moisture and keeps the relative humidity near zero so that the dish or sample will not gain weight from absorbed moisture.
The development of vertical mining within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life. This vertical mixing can be caused by mechanical means (pump) or through the use of forced air diffusers which release air into the lower layers of the reservoir.
A sulfate-reducing bacteria in water which can convert sulfates and elemental sulfur to sulfide, thereby creating hydrogen sulfide gas and the concomitant "rotten egg" odor in water supplies. See Also: Thiobacillus Sulfur (S) Thiobacillus Crenothrix Polyspora Cyclospora Cyanobacteria-like Bodies (CLBs) Gallionella Ferruginea Organic Iron Organism Thiobacillus Thiobacillus
The time period between the moment a change is made and the moment when such a change is finally sensed by the associated measuring instrument.
1. The theoretical (calculated) time required for a small amount of water to pass through a tank at a given rate of flow. 2. The actual time in hours, minutes, or seconds that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber. In storage reservoirs, detention time is the length of time entering water will be held before being drafted for use (several weeks to years, several months being typical). Detention Time (hr) = Basin Volume (gal.)(24 hr/day)/Flow (gal/day)
Any material with cleansing powers: soaps, synthetic detergents, man-made alkaline materials, solvents, and abrasives. In common domestic usage, the term is often used to refer to synthetic detergents. See Also: Base Alkali Alkalinity Alkalinity Tests Hydroxide Alkalinity Methyl Orange Methyl Orange Alkalinity Phenolphthalein Phosphate Soap Soap Phosphate Sodium Carbonate Soap
The temperature to which air must be cooled to cause condensation of the water vapor it contains.
1. To remove or separate a portion of the water present in a sludge or slurry. To dry sludge so it can be handled and disposed. 2. To remove or drain the water from a tank or a trench.
A corrosion process that removes zinc from brass but leaves the copper in place; the brass (valve or fitting) retains its original dimensions but is severely weakened and is prone to structural failure, leaks, or seepage through the body walls. Occurs most readily in waters with high chlorides and pH greater than eight.
The separation of components of a solution by diffusion through a semipermeable membrane which is capable of passing certain ions or molecules while rejecting others. See Also: Ion Exchange Membrane
A form of positive displacement pump in which the reciprocating piston is separated from the solution by a flexible diaphragm, thus protecting the piston from corrosion and erosion and avoiding problems with packing and seals.
A type of microscopic algae with cell walls that contain silica.
A filtration method resulting in substantial particulate removal, that uses a process in which: 1. A "precoat" cake of diatomaceous earth filter media is deposited on a support membrane (septum); and 2. While the water if filtered by passing through the cake of the septum, additional filter media, known as "body feed," is continuously added to the feedwater to maintain the permeability of the filter cake.
A processed, natural material, chiefly the skeletons of diatoms, used as a filter medium.
A molecule containing only two atoms, such as hydrogen as H2 or oxygen as O2.
Dissolved Inorganic Carbon.
A plumbing fitting made of an electrical nonconductor (such as plastic) used to control galvanic corrosion when joining pipes of dissimilar metals (such as copper and galvanized steel). If the dielectric fitting is used in a main water line, a bypass strap may be necessary to maintain the continuity of existing electrical grounding since the household water pipes may have been used to ground the household electrical lines.
The difference in pressures at two points in a water system; may be due to differences in elevation or to friction losses or pressure drops due to resistance to flow in pipes, softeners, filters or other devices.
See Distributor.
The process whereby particles of liquids intermingle as the result of their spontaneous movement in dissolved substances moving from a region of high concentrations to one of low concentration.
A chemical feed system in which chemicals are added to a water stream in controlled quantities for pipe line or metal surface protection and/or disinfection methods. A diffusion feeder is designed in such a way that a small stream of water is diverted through a tank so that the water flows over the chemical material (or solution), a small amount of which is diffused (dissolved) into the water and carried back to the main water line. A diffusion feeder is also called a bypass feeder.
The process by which complex organic materials are broken down and decomposed into simpler substances as a result of a chemical or biological reaction or a combination of reactions. Aerobic digestion takes place in the presence of air; anaerobic digestion takes place in the absence of air.
Use of numbers to indicate the value or measurement of a variable. The readout of an instrument by a direct, numerical reading or the measured value.
Water (H2O).
A solution that has been made weaker, usually by the addition of water.
The act of adding more solvent or water to a given solution to make it less concentrated. Sometimes this is done to attain the proper concentration; sometimes to make the solution easier to handle.
Lakes and reservoirs which freeze over and normally go through two stratification and two mixing cycles within a year.
Demand Initiated Regeneration.
Electrical current flowing in one direction only and essentially free from pulsation.
A filtration method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. The flocculation facilities may be omitted, but the physical/chemical reactions will occur to some extent. The sedimentation process is omitted. See Also: In-line Filtration Conventional Filtration In-line Filtration Normal Flow Filtration Cross flow filtration Conventional Filtration Conventional Filtration In-line Filtration Normal Flow Filtration Cross flow filtration
Water that flows over the ground surface or through the ground directly into streams, rivers, or lakes.
The pressure (in pounds per square inch or psi) measured at the center line of a pump discharge and very closely to the discharge flange, converted into feet.
To free from infection by either a chemical or physical means; causing the absence of pathogenic or indicator coliform bacteria in drinking water. Disinfectants kill or inactivate 99.9 to 99.9999 percent (but not 100%) of microorganisms under controlled conditions. Some common disinfectants are the halogens: chlorine, iodine, bromine, and hypochlorites; ozone, potassium permanganate, hydrogen peroxide, peracetic acid; formaldehyde, glutaraldehyde, phenol (carbolic acid), organic acids, benzoic and salicylic acids and their sodium salts, high pH, heat, ionizing radiation, and electromagnetic waves such as those of ultraviolet light. The USEPA requires that a disinfection claim must show killing or inactivation of all vegetative microbes in 10 minutes. See Also: Sterilization Antiseptic Aseptic Aseptic Procedure Sterilize Sanitization Sanitizer Biocide Antiseptic Aseptic Aseptic Procedure Sporicide Sanitization Sanitize
A process in which pathogenic (disease producing) bacteria are killed; may involve disinfecting agents such as chlorine or physical processes such as heating.
A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.
A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.
A material that increases the stability of particles in a liquid.
Any component of a piece of water treatment equipment or water treatment system which is manufactured to be disposed of instead of repaired or reused. Example: A cartridge filter element.
The separation of molecules into positively and negatively charged ions in water solution.
The fraction of inorganic carbon (the carbonate, bicarbonate, and dissolved CO2) in water that passes through a 0.45 micron pore-diameter filter.
That portion of matter or solids, exclusive of gases, which is dispersed in water to produce a homogenous liquid. According to the definition used in the water treatment industry, "dissolved matter" is that portion of the total matter that will pass through a 0.45 micron pore-diameter membrane filter.
The fraction of total organic carbon (all carbon atoms covalently bonded in organic molecules) in water that passes through a 0.45 micron pore-diameter filter. See Also: Carbonate Hardness Bicarbonate Hardness Hardness Dissolved Solids Residual Chlorine Residue Iron (Fe) Heme Tannin Total Organic Carbon (TOC) Calcite Carbon Dioxide Carbonate Hardness Bicarbonate Hardness Hardness Hardness as Calcium Carbonate Plastic Pipe Calcium Carbonate Total Hardness (TH) Total Organic Carbon (TOC) Soda Ash
Measure of water quality indicating free oxygen dissolved in water.
The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105o or 180o C
The product water or condensate, which is mineral-free and potable, from a distiller unit.
The process of separating the water from the organic and inorganic contaminants through a combination of evaporation (or vaporization), cooling, and condensation.
Water which has been cleansed by passing through one or more evaporation-condensation cycles until it contains a very low amount of dissolved solids (usually less than 5.0 ppm TDS).
(See Collector)
[die-VAY-lent] Having a valence of two, such as the ferrous ion, Fe2+. Also called bivalent.
1. Use of part of a stream flow as a water supply. 2. A structural conveyance (or ditch) constructed across a slope to intercept runoff flowing down a hillside, and diverting it to some convenient discharge point.
A polymerization monomer used as a cross-linking agent by polymerization with styrene in the manufacture of many synthetic ion exchange resin products. The degree of DVB cross-linkage is a factor in exchanger resistance to chemical oxidation. Standard cation resin usually contains about 8% DVB. Macroporous resins contain over 12% DVB cross-linking. See Also: Backflow XPLE or PEX Macroporous Resin Normal Flow Filtration Polyethylene Cross-linked Polyethylene (XLPE or PEX) XPLE or PEX Cross-linked Polyethylene (XLPE or PEX)
Dissolved Organic Carbon.
A specific form of limestone (CaMg(CO3))2 containing chemically equivalent concentrations of calcium and magnesium carbonates: the term is sometimes applied to limestones with compositions similar to true dolomite.
A slang term sometimes applied to water conditioning equipment designed for residential use.
The quantity of a chemical administered to an organism.
The actual quantity of a chemical to which an organism is exposed.
The product of the absorbed dose from ionizing radiation and such factors as account for differences in biological effectiveness due to the type of radiation and its distribution in the body as specified by the International Commission on Radiological Units and Measurements (ICRU).
A quantitative relationship between the dose of a chemical and an effect caused by the chemical.
A graphical presentation of the relationship between degree of exposure to a chemical (dose) and observed biological effect or response.
A component of risk assessment that describes the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease.
The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury produced.
The direction that groundwater flows; similar in concept to downstream for surface water, such as down river.
The softening process in which raw water enters at the top of the softener bed column and passes downward through the cation resin and out the bottom. In this process, the brining would also be in this same cocurrent direction.
A term applied to designate the direction (down) in which water or a regenerant flows through an ion exchanger or filter during any phase of the operating cycle. Also referred to as co-current flow.
A method of measuring the chlorine residual in water. The residual may be determined by either titrating or comparing a developed color with color standards. DPD stands for N,N-diethyl-p-phenylene-diamine.
1. The act of drawing or removing water from a tank or reservoir. 2. The water which is drawn or removed from a tank or reservoir.
A pipe, conduit, or receptacle in a building which carries liquids by gravity to waste. The term is sometimes limited to refer to disposal of liquids other than sewage.
A pipeline which is used to carry backwash water, regeneration wastes, and/or rinse water from a water treatment system to a drainage receptacle or waste system.
A technique to improve the productivity of some agricultural land by removing excess water from the soil; surface drainage is accomplished with open ditches; subsurface drainage uses porous conduits (drain tile) buried beneath the soil surface.
The area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel.
1. The drop in the water table or level of water in the ground when water is being pumped from a well. 2. The amount of water used from a tank or reservoir. 3. The drop in the water level of a tank or reservoir.
The loss of water that is entrained in the stack discharge.
A well constructed by either cable tool or rotary methods which operates by cutting or abrasion; materials are brought to the surface by means of a hollow drill tool, a boiler, a sand pump, or by another hydraulic and/or self-cleaning method.
1. A water, treated or untreated, which is intended for human use and consumption and considered to be free of harmful chemicals and disease-causing bacteria, cysts, viruses, or other microorganisms. 2. Safe water that has been further treated to enhance aesthetic quality and/or reduce mineral content by one or more point-of-use processing devices. See Also: Safe Water Aesthetic Contaminants Health Contaminant Drinking Water Standards Potable (Drinking) Water Safe Drinking Water Act (SDWA) Safe Water Club Soda Community Water System Zone of Saturation Bottled Artesian Water Bottled Distilled Water Bottled Fluoridated Water Bottled Mineral Water Bottled Natural Water Lime Soap Bottled Spring Water Brackish Water Brine Internal Water Treatment Ion Exchange Aesthetic Contaminants Health Contaminant Drainage Basin Drinking Water Standards Municipal Water Permutit Process Phosphate Potable (Drinking) Water Etching External Water Treatment United States Pharmacopeia (USP) Water Softening WFI Sulfur (S) Safe Drinking Water Act (SDWA) Safe Water Sewage Silica Sodium Carbonate Softened Water Soft Water
Standards that define allowable water quality limits for potable and domestic water supplies. The U.S. Environmental Protection Agency (EPA) is responsible for the National Primary Drinking Water Regulations, which are health-related standards that establish the Maximum Contaminant Levels (MCLs) for regulated substances in drinking water. An MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. MCLs are enforceable at public water systems under the Safe Drinking Water Act. The EPA also has set Maximum Contaminant Level Goals (MCLGs) at levels which no known or anticipated adverse effects on the health of persons occur and which allow an adequate margin of safety. The enforceable MCL is set as close to the MCLG as reasonable, taking into consideration the costs and treatment techniques available to public water systems. National Secondary Drinking Water Regulations, also issued by the EPA, pertain to aesthetic characteristics of water and are advised, but not enforceable, by the Federal government. See Also: Yield Potable (Drinking) Water Aesthetic Contaminants Health Contaminant Drinking Water Potable (Drinking) Water Safe Drinking Water Act (SDWA) Safe Water Club Soda Community Water System Zone of Saturation Bottled Artesian Water Bottled Distilled Water Bottled Fluoridated Water Bottled Mineral Water Bottled Natural Water Lime Soap Bottled Spring Water Brackish Water Brine Internal Water Treatment Ion Exchange Aesthetic Contaminants Health Contaminant Drainage Basin Drinking Water Municipal Water Permutit Process Phosphate Potable (Drinking) Water Etching External Water Treatment United States Pharmacopeia (USP) Water Softening WFI Sulfur (S) Safe Drinking Water Act (SDWA) Safe Water Sewage Silica Sodium Carbonate Softened Water Soft Water Crenothrix Polyspora Cyclospora Biostat Cyanobacteria-like Bodies (CLBs) Gallionella Ferruginea Organic Iron Organism Oxidation Oxidize Oxidizing Agent Alkylaryl Sulfonate Alkylbenzene Sulfonate (ABS) Desulfovibrio Potable (Drinking) Water Emulsification Redox Retention Wetting Agent Thiobacillus Thiobacillus
A shallow, usually small well (having a diameter of 1.5 inches to 3 inches or 4 to 10 cm) constructed without the aid of any drilling, boring, or jetting device, by driving a series of connected pipe lengths into unconsolidated material to a water-bearing stratum.
A brine tank, usually full of undissolved salt and with saturated brine below the undissolved salt. This is the type of brine tank used with most automatically-regenerated home softeners because it reduces the frequency of refilling the tank with salt. See Also: Wet-Salt Saturator Tank Wet-Salt Saturator Tank Septic System Service Unit
A water processing system composed of two separate tanks (or compartments) vertically connected, one above the other and operated by one common set of (master) valve controls. Example: filter (top) and softening unit below (bottom).
Any filter or ion exchange media which is used to perform two treatment steps in an application. Example: activated carbon filtration and adsorption; or cation resin softening and dissolved iron removal.
A shallow, large diameter well constructed by excavating with power machinery or hand tools instead of drilling or driving. Typically a dug well is constructed for an individual residential water supply and yields considerably less than 100 U.S. gallons per minute (380 L/min.)
Divinylbenzene.
Estimated exposure (in mg/L) which is interpreted to be protective for noncarcinogenic endpoints of toxicity over a lifetime of exposure. DWEL was developed for chamicals that have a significant carcinogenic potential (Group B). Provides risk manager with evaluation on noncancer endpoints, but infers that carcinogenicity should be considered the toxic effect of greatest concern.
Active, alive, or tending to produce motion as opposed to static, resting, or fixed.
When a pump is operating, the vertical distance (in feet) from a reference point (such as a pump center line) to the hydraulic grade line is the dynamic head.
An ion exchange reaction which takes place as the water moves past the exchange resin or resins.
A system or process in which motion occurs, or includes active forces, as opposed to static conditions with no motion.
The water pressure at the inlet to a dynamic water processing system.