A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

VACUUM BREAKER - A mechanical device which automatically vents a water line to the atmosphere when subject to a partial vacuum, thus preventing back siphonage.

VACUUM DISTILLATION - Distillation that occurs at a pressure somewhat below atmospheric pressure. Lowering the pressure also lowers the boiling point of water, thus conserving energy by requiring less heat to bring about distillation.

VACUUM FILTRATION - The filtration process in which a partial vacuum is applied to increase the rate of filtration by causing the water to be sucked through the filter medium. This is one of the oldest mechanical dewatering techniques in continuous use. In municipal softening, this process is used to separate water from the lime sludge for sludge disposal.

VACUUM FREEZING - A form of desalination using a vacuum to help cool and fast freeze high TDS source water which separates the solids by concentrating them in the portion of the water that doesn't freeze or that freezes last in a similar manner to what occurs in the cloudy centers of ice cubes.

VACUUM PAN - An airtight container used to produce granulated water softener salt using a process involving the evaporation of brine-turned-to-steam in a partial vacuum.

VACUUM PUMP - A pumping apparatus which exhausts gas or air from an enclosed space to achieve a desired degree of vacuum.

VALENCE - A whole number (positive or negative) representing the power of one element to combine with another. In general terms, the valence number represents the number of electrons in an atom or combined group of atoms which can be easily given up or accepted to react with or bond to another atom or group of atomes to form a molecule.

VALIDATION - 1. (water treatment industry) Determination upon testing that a representative sample of a water treatment equipment model has met the requirements of a specified standard. 2. (pharmaceutical industry) The requirement of certain quality control testing and record keeping procedures to ensure compliance not only with a specific quality but also with a specific means to achieve and encore that quality.

VAN DER WAAL'S FORCES - Weak attractive forces acting between molecules. These forces are somewhat weaker than hydrogen bonds and far weaker than interatomic valences.

VAPOR - 1. The gaseous form of any substance whose usual forte is a liquid or a solid. 2. Visible particles of moisture suspended in air, such as mist or fog.

VAPOR PRESSURE - The pressure, often expressed in millimeters of mercury (mm Hg, at which a vapor is in a state of balance with its liquid or solid form.

VARIABLE COSTS - Input costs that change as the nature of the production activity of its circumstances change; for example, as production levels vary.

VARIANCE - A State with primary enforcement responsibility under the Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL by granting a variance if certain conditions exist. These are: 1) the system cannot meet the MCL in spite of the application of best available treatment technology, treatment techniques, or other means (taking costs into consideration), due to the characteristics of the raw water sources which are reasonably available to the system, and 2) the variance will not result in an unreasonable public health risk. A system may also be granted a variance from a specified treatment technique if it can show that, due to the nature of the system’s raw water source, such treatment is not necessary to public health.

VEGETATIVE CONTROLS - Nonpoint source pollution control practices that involve planet (vegetative cover) to reduce erosion and minimize the loss of pollutants.

VELOCITY (GENERAL WATER TREATMENT) - The time measurement of linear motion (flow) in a given direction. For example, water flowing 60 feet in a conduit each minute has a velocity of 60 feet per minute (fpm) or one foot per second (1 fps).

VELOCITY PROFILE - The relationship between the velocity of fluid flowing adjacent to the conduit wall or membrane surface and that flowing at a distance from the wall or surface.

VENTURI - A tube with a narrow throat (a constriction) that increases the velocity and decreases the pressure of the liquid passing through it, creating a partial vacuum immediately after the constriction in the tube. The vacuum created has a sucking effect (eduction), and a venturi is commonly used to introduce a liquid (such as a regenerant) or gas (such as air) into a flowing water scream.

VERSENATE - A chemical substance used in water analysis for water hardness or with an indicator to colorimetrically measure hardness quality.

VIABLE - 1. Capable of living independently (as in a fetus capable of living outside the womb) and being reproductive (as microorganisms capable of colonizing and thriving) 2. workable (as a viable idea).

VIABLE TREATMENT PROCESS - A water or waste water treatment process capable of accomplishing the desired water quality.

VIRULENCE - Degree of ability to cause disease.

VIRUS - A parasitic infectious microbe, composed almost entirely of protein and nucleic acids, which can cause disease(s) in humans. Viruses can reproduce only within living cells. They are 0.004 to 0.1 microns in size, and about 100 times smaller than bacteria.

VISCOSITY - The tendency of a fluid to resist flowing due to internal forces such as the attraction of the molecules for each other (cohesion) or the friction of the molecules during flow. Viscosity varies with water temperature.

VOCs - volatile organic chemicals.

VOIDs - SEE void volume.

VOID VOLUME - The volume occupied by the interstitial spaces between the particles of ion exchangers, filter media, or other granular materials in a bed or column. Often expressed as percent of the total volume occupied by the medium bed.

VOLATILE - Capable of becoming vapor at relatively low temperatures.

VOLATILE ACIDS - Acids produced during digestion. Fatty acids which are soluble in water and can be steam-distilled at atmospheric pressure. Also called organic acids. Volatile acids are commonly reported as equivalent to acetic acid.

VOLATILE LIQUIDS - Liquids which easily vaporize or evaporate at room temperatures.

VOLATILE ORGANIC CHEMICALS (VOCs) - Organic chemicals that turn into vapor at relatively low temperatures.

VOLATILE SOLIDS - The term used in the laboratory analysis of the solids content of a substance (such as water) to define the portion of the total suspended and/or dissolved solids that become expulsed or driven off after heating or burning a given sample of the substance at a specified temperature and for a specified time.

VOLATILIZATION - Loss of a substance through evaporation.

VOLTAGE - The electrical pressure available to cause a flow of current (amperage) when an electrical circuit is closed.

VOLUMETRIC - A measurement based on the volume of some factor. Volumetric titration is a means of measuring unknown concentrations of water quality indicators in a sample by determining the volume of titrant or liquid reagent needed to complete particular reactions.

VORTEX - A revolving mass of water which forms a whirlpool. This whirlpool is caused by water flowing out of a small opening in the bottom of a basin or reservoir. A funnel-shaped opening is created downward from the water surface.

WASTE WATER - Water that has been used. 1. (RO, ultrafiltration, electrodialysis) The stream of water (not product water) created as the result of processing water-the reject water or concentrate. 2. (ion exchange and filtration) The spent water used in the total backwash and/or regeneration cycle. 3. The used water and solids from a residence or a community (including used water from industrial processes) that flow to a septic system or a treatment plant. Storm water, surface water, and groundwater infiltration also may be included in the waste water that enters a waste water treatment plant. The term sewage usually refers to household wastes, but this word is being replaced by the term waste water.

WASTE WATER TREATMENT PLANT - A facility that receives waste waters (and sometimes runoff) from domestic and/or industrial sources, and by a combination of physical, chemical, and biological processes reduces (treats) the waste water to less harmful byproducts; known by the acronyms WWTP, STP (sewage treatment plant), and POTW (publicly owned treatment works).

WATER (H₂O) - An odorless, colorless, tasteless liquid which exists as ice in solid form (phase) and steam in vapor form (phase). It freezes at 32°F (0°C) and boils at 212°F (100°C). Water is a polar squid with high dielectric constant which accounts for its solvent power, it is called the universal solvent. It is a weak electrolyte; in pure water, only about two molecules in every 1,100,000,000 separate into H₃O⁺ and OH- ions. Water is only slightly compressible. It is the liquid that descends from the clouds as rain and forms lakes, streams, and seas (oceans). Water is a major constituent of all living matter. Also referred to as H₂O (dihydrogen oxide) and HOH (hydrogen hydroxide).

WATER BLOOM - A prolific growth of plankton, including blue-green algae, which may occur and be so dense that it imparts a greenish, yellowish, or brownish color to water near the surface of a lake, pond, or reservoir.

WATERBORNE DISEASE - A disease, caused by a bacterium or organism able to live in water, which can be transmitted by water.

WATERBORNE DISEASE OUTBREAK - The significant occurrence of acute infectious illness, epidemiologically associated with the ingestion or water from a public water system that is deficient in treatment, as determined by the appropriate local or state agency.

WATER BUDGET - A summation of inputs, outputs, and net changes to a particular water resource system over a fixed period. (Also, water balance model.)

WATER CLOSET - A flushable toilet.

WATER CONDITIONING - The treatment or processing of water, by any metals, to modify, enhance, or improve its quality or to meet a specific water quality need, desire, or set of standards. Also called water treatment.

WATER CYCLE - SEE hydrologic cycle.

WATER DENSITY (MAXIMUM) - The maximum density of water is reached at 39°F (4°C). It becomes less dense at both higher and lower temperatures.

WATER FLOODING - A process in underground mining such as oil recovery in which oil or a mineral from underground formations is replaced by an infusion of warm, softened water thus bringing the underground substance to the surface for recovery. Also known as oil well flooding.

WATER GLASS - The common name of a sodium silicate (Na₂O • xSiO₂) substance used for corrosion control in potable waters. It is also an ingredient used in the manufacture of synthetic gel zeolite.

WATER HAMMER - The shock wave or series of waves caused by the resistance of inertia to an abrupt change (acceleration or deceleration) of water flow through a water piping system. Water hammer may produce an instantaneous pressure many times greater than the normal pressure. For this reason, many building codes now require the installation of a "water hammer arrestor," a device to absorb these shock waves and prevent damage to appliances such as washing machines.

WATER JACKET - An outer casing which holds water or through which water flows and circulates to absorb heat and cool the interior of the mechanism or machinery that the water jacket is surrounding.

WATERLESS HAND CLEANER - A paste, gel, or lotion that does not require rinsing. Waterless hand cleaners are useful when facilities for hand washing are not available and are also helpful in removing difficult soils. Available for use from dispensers, or directly from their own containers, they are usually oil-in-water emulsions. They are available with or without srubbers. The scrubbers may be organic, (e.g., particles of polyethylene or polystyrene) or inorganic (pumice).

WATERLOGGED TANK - A tank (as in a domestic water well pumping system) in which too much water has accumulated and has replaced some of the air in the tank's air cushion causing a disruption in the normal pressure pattern needed for pumping and uniform water flow.

WATER METER - An instrument, mechanical or electronic, used for recording (in gallons, cubic feet, or cubic meters) the quantity of water passing through a particular pipe line or outlet. In water processing system, meters may initiate certain functions such as automatically starting the regeneration cycle in an ion exchange system.

WATER OF HYDRATION - Water which has been chemically combined with a substance to form a hydrate and which can then be removed (as by heating) without essentially changing the chemical composition of the substance.

WATER PROCESSING - SEE water conditioning.

WATER PURVEYOR - An agency or person that supplies water (usually potable water).

WATER REGAIN - SEE water retention.

WATER RETENTION - The amount of water, expressed as a percent of the wet weight of an ion exchanger, retained within the resin bead and on the surface of fully swollen and drained ion exchange media. Also called water regain.

WATERSHED - The land area that drains into a stream. An area of land that contributes runoff to one specific delivery point; large watersheds may be composed of several smaller "subsheds", each of which contributes runoff to different locations that ultimately combine at a common deliver point.

WATER SOFTENER (CHEMICAL) - A compound which, when introduced into water used for cleaning or washing, will counteract the effects of the hard water minerals (calcium and magnesium) and produce the effect of softened water. For example, detergent additives and polyphosphates.

WATER SOFTENER (MECHANICAL) - A pressurized water treatment device in which hard water is passed through a bed of cation exchange media (either inorganic or synthetic organic) for the purpose of exchanging calcium and magnesium ions for sodium or potassium ions, thus producing a softened water which is more desirable for laundering, bathing, and dishwashing. This cation exchange process was originally called zeolite water softening or the Permutit Process. Most modern water softeners use a sulfonated bead form of styrene/divinylbenzene (DVB) cation resin.

WATER SOFTENER SALT - Salt suitable for regenerating residential and commercial cation exchange water softeners. Most commonly used for this purpose is sodium chloride (NaCl) in crystal or pelletized form. Rock grade salt should be 96-99 percent NaCl; evaporated salt should be 99+ percent NaCl. Potassium chloride (KCl) may also be used for the regeneration cycle in the cation exchange process, thus minimizing the amount of sodium added to both the softened water and the spent regenerant water going to the drain.

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

WATER SOLUBILITY - The maximum concentration of a chemical compound which can result when it is dissolved in water. If a substance is water soluble, it can very readily disperse through the environment.

WATER SOURCE - The basic origin of a water, either a surface source (such as a lake, river, or reservoir) or a subsurface source (such as a well). After treatment and pumping via pipe lines, the treated and pumped water becomes a wafer supply.

WATER SPOTTING - Cloudy milk-like film, spots, streaks, or heavy white deposits left on surfaces after water has dried from them, especially noticeable on clear glassware and cars after washing. Spotting is caused by minerals that had been dissolved in the water remaining behind alter the water has evaporated away. Soft water spotting can be wiped off easily with a damp cloth or rinsed off with a little fresh water. Hard water deposits, on the other hand, are comprised of the more tenacious calcium and magnesium salts. Hard water films typically require harsh abrasives or an acid cleaner to remove them. A third type of water residue film is due to silica (SiO₂) deposits. Silica spotting is rare, but it is more difficult or impractical to be removed when it does occur. If glassware films won't dissolve in acids such as vinegar or lemon juice, they may be due to silica spotting or etching. If the spot won't dissolve in acid, but can be scratched off with a razor blade or pinpoint, it's likely a silica film.

WATER STORAGE POND - An impound for liquid wastes, so designated as to accomplish some degree of biochemical treatment of the wastes.

WATER SUPPLIER - A person who owns or operates a public water system.

WATER SUPPLY SYSTEM - The collection, treatment, storage, and distribution of potable water from source to consumer.

WATER TABLE - The level of groundwater. The upper surface of the zone of saturation of groundwater above an impermeable layer or soil or rock (through which water cannot move) as in an unconfined aquifer. This level can be very near the surface of the ground or far below it. SEE ALSO zone of saturation.

WATER TREATMENT - SEE water conditioning.

WATER TREATMENT DEVICE - Any point-of-use or point-of-entry instrument or contrivance sold or offered for rental or lease for residential use, and designed to be added to the plumbing system, or used without being connected to the plumbing of a water supply intended for human consumption in order to improve the water supply by any means, including, but not limited to, filtration, distillation, adsorption, ion exchange, reverse osmosis, or other treatment.

WATER TREATMENT LAGOON - An impound for liquid wastes, so designed as to accomplish some degree of biochemical treatment of the wastes.

WATERTIGHT - A condition existing in water treatment equipment and materials of such precision of construction and fit as to be impermeable to water unless sufficient pressure occurs to cause rupture.

WATER WELL - An excavation where the intended use is for the location, acquisition, development, or artificial recharge of groundwater (excluding sandpoint wells).

WATT - A unit of power equal to one joule per second. The power of a current of one ampere flowing across a potential difference of one volt.

WBA - Weak base anion exchanger.

WEAK ACID CATION EXCHANGERS - Those cation exchange products with functional groups which, in the hydrogen form, are not capable of splitting neutral salts to form their corresponding free acids. Weak acid cation exchange resins have a much higher (three to four times higher) regeneration efficiency than their strong acid counterparts, but in the hydrogen form can only exchange cations that are associated with alkalinity. The cations associated with sulfates, chlorides, and nitrates, for example, cannot be removed with weak acid cation exchanger in the hydrogen form. Hydrogen form weak acid cation exchangers that have been neutralized with sodium hydroxide to the sodium form, however, can effectively remove both carbonate and noncarbonate water hardness cations; thus weak acid cation resins can be used to soften wafers that, because of high total dissolved solids, are not possible or practical to treat with strong acid cation resins.

WEAK BASE ANION EXCHANGERS - Those anion exchange products with functional groups which are not capable of splitting neutral salts to form corresponding free bases, Weak base anion exchange resins have a much higher (three to four times higher) regeneration efficiency than their strong base counterparts, but can only exchange mineral acid anions such as sulfate, chloride, and nitrate. The anions associated with weak acids, such as carbonates, bicarbonates, silicates, and organic acids, for example, cannot be removed with weak base anion exchange. SEE ALSO free base form.

WEIGHT CONCENTRATION RATIO (ULTRAFILTRATION) - The ratio of the initial weight of the feedwater to the weight of the reject water remaining at any time during the ultrafiltration process.

WEIR -1. A dam-like wall or plate placed in an open channel and used to measure the flow of water. The depth of the flow over the weir can be used to calculate the flow rate, or a chart or conversion table may be used. 2. A wall or obstruction used to control flow (from settling tanks and clarifiers) to assure uniform flow rate and avoid short-circuiting.

WEIR DIAMETER - Many circular clarifiers have a circular weir within the outside edge of the clarifier. All the water leaving the clarifier flows over this weir. The diameter of the weir is the length of a line from one edge of a weir to the opposite edge and passing through the center of the circle formed by the weir.

WEIR LOADING - A guideline used to determine the length of weir needed on settling tanks and clarifiers in treatment plants. Used by operators to determine if weirs are hydraulically (flow) overloaded.

WELL - A bored, drilled, or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground.

WELL FIELD - Area containing one or more welds that produces usable amounts of water.

WELL HEAD-A particular well site location, as differentiated from other well site locations, that exist in the same water system.

WELL MONITORING - The measurement, by on-site instruments or laboratory methods, of the quality of water in a well.

WELL PLUG - A watertight and gaslight seal installed in a bore hole or well to prevent movement of fluids.

WET CHEMISTRY - Laboratory procedures used to analyze a sample of water using liquid chemical solutions (wet) instead of, or in addition to, laboratory instruments.

WETLANDS - Any number of tidal and nontidal areas characterized by saturated or nearly saturated soils most of the year that form an interface between terrestrial (landbased) and aquatic environments; include freshwater marshes around ponds and channels (rivers and streams), brackish and salt marshes; other common names include swamps and bogs.

WET-SALT SATURATOR TANK - A type of brine lank, so named because the saturated brine is always above the undissolved salt level, used on large commercial water softeners and older manual residential softeners. Most automatic home-sized water softeners now use dry-salt saturator tanks.

WETTING AGENT - A compound that increases the ability and speed with which a liquid displaces air from a solid surface, thus improving the process of wetting that surface. Wetting agents are all surfactants. They function by lowering surface and interfacial tension. Soap and detergent surfactants serve as wetting agents in washing products, in addition to their other functions. In automatic dishwashing, nonionic surfactants are sometimes introduced into the last rinse for the purpose of maximizing drainage of water from dishes and utensils.

WFI - Water for Injection.

WHO - World Health Organization.

WIRE-TO-WATER-EFFICIENCY - The efficiency of a pump and motor together. Also called the overall efficiency.

WITHDRAWAL - The process of taking water from a source and conveying it to a place for a particular type of use.

WORKING PRESSURE - SEE operating pressure.

WORLD HEALTH ORGANIZATION - A part of the United Nations. The WHO, which is headquartered in Geneva, Switzerland, has compiled recommended standards for drinking water.

XLPE - cross-linked polyethylene.

X-RAYS - 1. Electromagnetic radiation with a very short wavelength (0.01 to 12 nanometers), shorter than ultraviolet radiation. 2. An image created by short-term exposure of an object to x-rays used in spectrometry analysis and medical therapy.

YIELD - l. The amount of product water produced by a water treatment process. 2. The quantity of water (expressed as a rate of flow-GPM, GPH, GPD, or total quantity per year) that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations.

ZEOLITES - Hydrated sodium alumina silicates, either naturally-occurring mined products or synthetic products, with ion exchange properties. Zeolites were formerly used extensively for residential and commercial water softening but have been largely replaced by synthetic organic cation resin ion exchangers of polystyrene divinylbenzene substrate. Modified zeolites such as manganese greensand and synthetic manganese zeolites are still used as catalyst/oxidizing filters for the removal of iron, hydrogen sulfide, and manganese.

ZEOLITE SOFTENING - A term formerly used for the removal of calcium and magnesium hardness from water by base exchange using natural or synthetic zeolites. Since the introduction of synthetic organic cation exchange resins, the more correct term is cation exchange softening. Zeolite softening was also called base exchange.

ZERO DISCHARGE WATER - A discharge limit applied to manufacturing and commercial establishments in which only normal human sanitary waste waters may be discharged to the municipal sewerage system. All other types of waste water, such as that water used in manufacturing processes, are not included in zero discharge water; but they must be recycled, and the resulting waste product from such water must be taken to an alternate and approved disposal facility.

ZERO SOFT WATE - water produced by the cation exchange process and measuring less than 1.0 grain per U.S. gallon (17. 1 ppm or 17. 1 mg/L) as calcium carbonate. zeta potential-The electrical potential which exists across the interface of all solids and liquids. The potential represents the difference in voltage between the surface of the diffuse layer surrounding a colloidal particle and the bulk liquid beyond. Also known as electrokinetic potential.

ZONE OF AERATION - The comparatively dry soil or rock located between the ground surface and the top of the water table.

ZONE OF SATURATION - The layer in the ground in which all available interstitial voids (cracks, crevices, holes) are filled with water. The level of the top of this zone is the water table. SEE ALSO water table.

ZOOPLANKTON - Small, usually microscopic animals (such as protozoans), found in lakes and reservoirs.