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Ultrafiltration
A method of crossflow filtration (similar to reverse osmosis but using lower pressures) that uses a membrane to separate small colloids and large molecules from water and other liquids. The ultrafiltration process falls between reverse osmosis and microfiltration in terms of the size of particles removed, with ultrafiltration removing particles in the 0.002 to 0.1 micron range, and typically rejecting organics over 1,000 molecular weight while passing ions and smaller organics.

Ultrapure Water
Highly treated water that is deionized and mineral-free with high resistivity and no organics; it is usually used in the semiconductor and pharmaceutical industries. Ultrapure water is NOT considered biologically pure (potable) or sterile. There is no set numerical standard to determine exactly what ultrapure water is or should be.

Ultraviolet Absorber
Substances that absorb ultraviolet radiation (light). Ultraviolet absorbers are added to plastic (such as used in plastic tanks and fittings) and rubber products to make them less likely to decay as the result of absorbing ultraviolet rays.

Ultraviolet Chamber
The area where the water is irradiated with ultraviolet rays.

Ultraviolet Demand
The amount of ultraviolet rays required to inactivate certain microorganisms.

Ultraviolet Dosage
The amount of disinfectant ultraviolet rays delivered to the organisms in the water being disinfected. Dosage is a combination of UV intensity times the contact time and is measured in watt-seconds per square centimeter.

Ultraviolet (UV) Light
Radiation (light) having a wavelength shorter than 3900 angstroms the wavelengths of visible light, and longer than 100 angstroms, the wavelengths of x-ray’s. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum.

Underbed
A layer of gravel or grout used to fill the bottom curved base of a larger filter or softener tank, usually in a system with a header-lateral design.

Underdrain
The drainage piping arrangement to collect treated water at the bottom of the ion exchange or filter media beds.

Uniform Flow
A flow in which the feet per second velocity rates and directions are the same from point to point along the conduit.

Uniformity Coefficient
The measure of the variation in particle sizes of filter and ion exchange media. The uniformity coefficient is defined as the ratio of the sieve size that will permit passage of 60 percent of the media material by weight to the sieve size that will permit passage of 10 percent of the media material by weight. A uniformity coefficient of 1.00 denotes a material having particle grains all the same size; numbers increasingly greater than one denote increasingly less uniformity.

Uniform Particle Size
The particle size distribution screen sizing for exchanger and filtration media as established by U.S. Mesh Standards.

United States Pharmacopeia (USP)
The official publication for drug product standards including six water quality standards for pharmaceutical uses. The U.S. Congress established the USP in 1884 to control makeup of drugs.

Univalent
Having a valence of one. Also called monovalent.

Upflow
A pattern of water flow in which a solution (water or regenerant usually) enters at the bottom of the vessel or column and flows out at the top of the vessel or column during any phase of the treatment unit’s operating cycle. The term is used to describe ion exchange system flow patterns or water flow through filter media. A system can have upflow during the treatment cycle and downflow during regeneration. Upflow is also called countercurrent flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.

User
The product water consumer.

USP
United States Pharmacopeia.

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 atoms 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.

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.

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.

Viable Treatment Process
A water or waste water treatment process capable of accomplishing the desired water quality.

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.

Volatile Acids
Acids produced during digestion. Fatty acids that 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 that 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.

Water (H₂O)
An odorless, colorless, tasteless liquid that exists as ice in solid form (phase) and steam in vapor form (phase). It freezes at 32F (0C) and boils at 212F (100C). Water is a polar liquid with high dielectric constant that 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.

Waterborne Disease
A disease, caused by a bacterium or organism able to live in water, which can be transmitted by water.

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

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.

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.

Water Meter
An instrument, mechanical or electronic, used for recording the quantity of water passing through a particular pipeline 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 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.

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 softened water.

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 pellet 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 that 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 pipelines, the treated and pumped water becomes a wafer supply.

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.

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.

Weight Concentration Ratio
The ratio of the initial weight of the feed water to the weight of the reject water remaining at any time during the ultrafiltration process.

WFI
Water for Injection.

XLPE
cross-linked polyethylene.

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. 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.

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 wastewater, 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 Water
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 that 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.