Nanofiltration:
A cross flow membrane separation process which removes particles in the 250 to 1000 molecular weight range, selected salts and most organics; sometimes referred to as a softening membrane process.

Naturally soft water:
Ground, surface, or rain water sufficiently free of calcium and magnesium salts so that no curd will form when soap is used and no calcium or magnesium-based scale will form when the water is heated or frozen.

Nephelometer:
A device used to measure mainly low turbidity water with results expressed in Nephelometric Turbidity Units (NTU).

Nickel:
(Ni+2, MCL: 0.1 ppm)
Nickel is generally not a problem in drinking water, food and tobacco being the major sources. The metal is used in corrosion-resistant alloys and plantings for some food service equipment, so it may be found in highly corrosive environments. Generally, drinking water contains levels below 0.03 ppm.

Nitrate:
(NO3-, MCL: 10 ppm as N, 45 ppm as NO3-)
No3- ion is seldom present at significant levels except in areas with intensive agriculture. It is a major constituent of fertilizers applied to crops and of animal manure from beef, pork, and chicken production. It is important because intestinal bacteria readily convert nitrate into nitrite, NO2-, which is one of the causes of Sudden Infant Death Syndrome or "Blue Babies". Nitrite binds to infant hemoglobin and interferes with oxygen transmission until the age of about 3-6 months, at which time infant hemoglobin is replaced with adult hemoglobin, which is not sensitive to nitrite. Maximum safe levels are 45 M/L as Nitrate. Nitrate levels in drinking water normally do not exceed 20 ppm Nitrate (4 ppm as N) or 0.2 ppm Nitrite. Nitrite also combines with myoglobin in muscle tissue, thus preserving the colour of fresh meat even after cooking, causing a problem of consumer acceptance with light meats like chicken, which are marinated in sauces made from high-nitrite water. Reverse Osmosis is the usual remedy, although very costly ion exchange resins that are more or less specific for nitrate do exist.

Nominal filter rating:
Filter rating indicating the approximate size particle, the majority of which will not pass through the filter. It is generally interpreted as meaning that the filter will retain 85% of the particles of the size equal to the nominal rating, but this is not a guarantee that this will occur.

NSF:
National Sanitation Foundation, a third-party organization that tests foodservice equipment to exacting standards. NSF ratings insure that a product will; perform as promised, state clearly what the product will and won't do, and offer comparisons between various manufacturers' products.

NTU:
Nephelometric Turbidity Units- the result of passing a light beam through water sample with a nephelometer to quantify low-turbidity water. The NTU is measured by light scattering.

Odor:
(Secondary MCL: 3 T.O.N.)
All odors are gases, those dissolved in water are often dissipated during transit, and so they can change or disappear before the sample reaches the laboratory. Except for chlorine and iron, virtually all taste and odor (T&O) in water is microbial in origin. Common earthy-musty-fishy-moldy T&O is produced by algae in reservoirs, filamentous bacteria called actinomycetes, and also molds. Rotten egg odor is hydrogen sulfide produced by anaerobic bacteria deep in wells or in stagnant, dead-end pipes. Sometimes combinations of iron and sulfur bacteria produce strange "septic" smells. Finally, it is possible for marginal disinfection with chlorine or ozone to produce traces of phenol or phenolic compounds, which combine with the remaining traces of chlorine to produce chlorophenols, which are extremely potent producers of "medicinal" T&O. Odor is measured by trained people and reported as a "Threshold Odor number" (T.O.N.), which is the dilution factor required to make the odor disappear. A T.O.N. of 3 or less is considered acceptable. The preferred remedy is activated carbon filtration, which is very effective at removing nearly all foul tastes and odors, with the single exception of hydrogen sulfide. Carbon's capacity for hydrogen sulfide is quickly exhausted and chemical oxidation is always worthwhile.

Oxidize:
To increase a molecule in positive valence; to lose electrons to an oxidizing agent.

Oxidizing agent:
A chemical agent that gains electron (i.e. is reduced) and brings about the oxidation of other substances. Examples of oxidizing agents include oxygen, ozone, chlorine, and peroxide.

Oxidizing Filters:
Filters that use a catalytic medium such as manganese oxide to oxidize iron and manganese and then filter the impurities from the water after they have been oxidized.

Ozone (O3):
An unstable, highly reactive state of oxygen formed by passing air or oxygen through a high voltage electric charge or strong light source. An excellent oxidizing agent and bactericide.

Particulate:
Minute, separate pieces of matter.

Permeable:
Allowing some material to pass through.

Permeate:
The portion of the feed stream which passes through a membrane, leaving behind a more concentrated stream.

Permeator:
A hollow fine fiber membrane element itself consisting of thousands of hollow fibers.

pH:
(secondary MCL pH 6.5-8.5)
The term "pH" is chemist's jargon for the level of acidity in water. The hydrogen ion, H+, is the basis or embodiment of all acids and the pH scale indicates the concentration of H+. Values range from zero (extremely strong acid) to 14 (extremely strong base or alkali), with the neutral point in the middle at pH 7.0. It is a logarithmic scale, so values differing by one unit indicate ten-fold differences. Acidity of pH 5 is ten times more acid then pH 6, and 100 times more acid than pH 7. Carbonated beverages are usually pH 3-4, wines slightly lower, and stomach acid is pH 1. Blood and body fluids are pH 7.4, drinking water is usually pH 7-9, antacids are pH 10 or so, and lye or drain cleaners are pH 12-14. The pH of drinking water is important because "acidic water" (pH less than 7) is a major cause of corrosion, which may leach toxic levels of lead, copper, zinc, and cadmium from the plumbing. Scaling is prominent when pH values exceed 8.5 in combination with high hardness and alkalinity. Remedies entail a ding a chemical of the opposite character, to neutralize or consume the excess acidity or alkalinity. Acid waters are neutralized by the addition of sodium carbonate ("soda ash") or sodium hydroxide ("caustic soda"). Alkaline waters are treated with the addition of an acidulate such as food grade citric acid. Ion exchange can also be used to correct pH.

Phosphate:
(PO4-3, no MCL)
PO4-3 ion is not usually found as significant levels in tap water, but phosphate compounds are often intentionally added by the waterworks or by point-of-use treatment. Zinc orthophosphate is used to form a protective coating on the plumbing, to prevent corrosion and limit the leaching of copper and lead. Polyphosphates are polymers units, which are used to inhibit the formation and deposition of lime scale. Useful levels for scale reduction are in the range of about ½-10 ppm; more than 15 ppm may lead to deposition of "phosphate scale" (calcium phosphate) in very hard waters. In other words, too much polyphosphate actually makes the scale problem worse. In some water supplies phosphate is the nutrient most needed for microbial growth (the "limiting nutrient"). Thus, where bacterial re-growth is a problem, avoiding phosphate use may be beneficial to maintaining low plate counts.

Polyphosphate:
A form of phosphate polymer consisting of a series of condensed phosphoric acids containing more than one atom of phosphorous.

Pore:
An opening in a membrane or filter matrix.

Porous:
The ability of certain substances to pass fluids due to an open physical structure.

Potable (drinking) water:
A water supply which meets U.S. E.P.A and/or state water quality standards and that is considered safe and fit for human consumption.

Potassium:
(K+, no MCL)
K+ ion is similar to sodium in being common, non-toxic, and widespread, but it is usually only a very minor constituent. Presence of a substantial level may be a sigma functioning softener using potassium chloride (KC1) in place of sodium chloride (NaC1). Filtration will not alleviate this problem.

POU:
Point of Use

ppb:
Parts per billion, commonly considered equivalent to micrograms per liter (ug/L).

ppm:
Parts per million, commonly considered equivalent to milligrams per liter (mg/L).

ppt:
Parts per trillion, commonly considered equivalent to nanograms per liter (ng/L)

Precipitate:
An insoluble product that is in the solution or liquid mixture.

Precipitation:
The process of producing an insoluble reaction product from a chemical reaction, usually a crystalline compound that grows in size to be settleable.

Precoat:
The application, usually by slurry, of a very fine granular filter medium such as diatomaceous earth to a retaining membrane or fabric surface prior to a service run. Precoat filtration is used in applications almost exclusively in the cartridge format. Precoat filters have a very high dirt holding capacity. The precoat cake is more stable than the granular media depth filters. It is unusual to find water pressures high enough to break through a precoat. Research and actual usage indicate the gallonage is increased by the square of the area increase. For example, tripling the area by using three precoat filters in parallel does not produce triple the capacity, it produces 3 squared or 9 times the capacity. Precoat filters are also capable of removing asbestos fibers to an acceptable level. Another area where the precoat process has found application is in cyst removal. Precoat filtration has been shown to remove Giardia and cryptosporidium over a broad range of operating conditions typical of potable water filtration.

PSI:
Pounds per square inch (pressure).

PSID:
Pounds per square inch differential.

PSIG:
Pounds per square inch gauge.

Pure water:
This term has no real meaning unless the word "pure" is defined by some standard. The Water Quality Association recommends against the use of the words "Pure Water" in advertising unless the meaning of "pure" is very clearly explained for the consumer.

Rated capacity:
(filtration or adsorption) The manufacturer's statement regarding the expected number of days the equipment will be in service or the expected number of gallons of product water delivered before service is required or flow rates diminish to an unacceptable level.

Rated service flow:
The manufacturer-specified maximum and minimum flow rates at which a particular piece of water treatment equipment will continuously produce the desired quality of water.

Residual chlorine:
Chlorine allowed to remain in treated water after a specified period of contact time and to provide disinfection protection throughout the distribution system. Residual chlorine is the difference between the total chlorine added and that consumed by the oxidizable matter. Residual chlorine may be evident by taste or odor in municipal water.

Resins:
(ion exchange): Specially manufactured polymer beads used in the ion exchange process to remove dissolved salts from water.

Resistivity:
The property of a substance (in this case, water) to resist the flow of electricity; the measurement of that resistance. The inverse of conductivity. Measured by a resistivity monitor and described in megohm-cm.

Reverse osmosis (RO):
A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semi permeable membrane. This is called "reverse osmosis" because the pressure forces the water to flow in the reverse direction than that of natural osmosis. (Natural osmosis is the flow from a diluted to a concentrated solution. Reverse osmosis is the flow from a concentrated to a diluted solution).

Saturation:
The point at which a solution contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.

Scaling:
The buildup of precipitated salts on such surfaces as pipes, tanks, and boiler condensate tubes.

Screen:
A term commonly used for septum. Also a wire mesh screen used to screen out large sized particles that would clog a filter cartridge. Usually installed on the suction side of a pump.

SDI:
Silt Density Index- test used to measure the level of suspended solids in feed water for a reverse osmosis system.

Selenium:
(Se, MCL: 0.05 ppm: under review)
Selenium is chemically similar to sulfur and occurs in water as selenate, SeO4-2, and selenite, SeO3-2 ions (analogous to sulfate and sulfite). Selenium is an unusual contaminant in that it is also a required nutrient, and adverse health effects are nearly as often due to selenium deficiency as to selenium poisoning. However, no "minimum MCL" has been proposed for water, because water is not supposed to be treated as a nutritional source, and almost all selenium exposure is via food, not water. Selenium levels in drinking water generally are well below 0.05 ppm, seldom exceeding 0.005 ppm.

Semipermeable:
In membranes, a membrane which allows a solvent such as water to pass through, while rejects certain dissolved or colloidal substances.

Septum:
A binding wall or membrane.

Silica:
(SiO2, no MCL)
True silica is insoluble glass or sand, silicon dioxide (SiO2), but the term as used in water treatment includes a host of "silicate" ions including SiO3-2 and SiO4-. All are very common (silica and compounds such as aluminum silicate are the predominant minerals of the Earth's crust), and their chemistry is complex. A very hard, glassy scale often forms on heat-exchange surfaces when SiO2 levels exceed 15-20 mg/L, and it cannot be removed with acid or inhibited with polyphosphates. There is no good remedy for silica scale. Lower concentrations are sometime intentionally added as corrosion inhibitors to produce a "glass lining" on pipes. In drinking water, it ranges from 0-75 mg/L with an average of 7 ppm. Filtration will not remedy silica.

Silver:
(Ag+, secondary MCL: 0.1 ppm)
The Ag+ ion only rarely occurs in natural waters, but it is an intentional additive of many water filters because of its weak bacteriostatic effect. Drinking water levels generally never reach levels of 0.04 ppm, and filters containing silver must not exceed .05 ppm Ag feed based on EPA pesticide limits.

Sodium:
(Na+, Secondary MCL: 250 mg/L proposed)
Na+ is almost always present in tap water, but it is seldom a major problem. The "salty" taste may be detectable by some people at levels as low as 50 ppm, and most people find water with more than 350 ppm hardness unpalatable. In drinking water, the range is usually 0-100 ppm. Levels of sodium higher than 100 ppm suggest a malfunctioning softener or sea water intrusion. Reverse Osmosis is the only remedy.

Soft water:
Any water which naturally contains less than 1.0 grain per gallon (17.1 mg/L or ppm) of total hardness expressed as calcium carbonate equivalent. SEE ALSO hard water.

Softened water:
Any water which has been processed in some manner to reduce the total hardness to 1 grain per gallon (17.1 mg/l or ppm) or less expressed as calcium carbonate equivalent.

Spring water:
Water obtained from an underground formation from which water flows naturally to the surface, or would flow naturally to the surface if it were not collected underground.

Static:
Fixed in position, resting; without motion.

Submicron filter:
A cartridge-type membrane filter used in fine particle separation applications to remove particulates of less that one-micron in size.

Sulfate:
(SO4-2, MCL: 250 ppm proposed)
SO4-2, ion is common in water but is usually limited to concentrations less than 50 ppm on average and range from 1 ppm to 800 ppm. No adverse health effects have been found to date for levels lower than 500 ppm, but levels above 1,000 ppm have caused diarrhea. Taste threshold is as low as 200 ppm. The suggested upper limit for potable water is 250 mg/L. Levels in the hundreds of ppm contribute to scaling in hot or cold applications when sufficient calcium or magnesium is present.

Sulfide:
(S-2, no MCL)
This S-2 ion is derived from hydrogen sulfide gas, H2S, which is the basis of "rotten egg" smell. H2S is highly toxic to breathe, but poisonings are extremely rare due to its obnoxious nature. Sulfide dissipates from water samples quickly, so it must either be analyzed on site or the sample must be stabilized with other chemicals immediately. However, formal analysis is seldom needed, since the human nose is a superior detector. In addition to the smell, hydrogen sulfide is an acid and therefore corrosive, so it is important to remove it even if people become tolerant of the smell. These are two approaches to remedying a rotten egg smell. In a municipal system with central treatment the best thing is to complain to the waterworks and demand that they flush out the mains regularly and get fresh, oxygenated water into the dead ends. The bacteria that make hydrogen sulfide are killed by dissolved oxygen, and the sulfide itself is readily oxidation system must be installed. A chlorination or ozonation system is best, because disinfection will be accomplished at the same time. Alternately, special oxidizing media called manganese greensand can oxidize without disinfecting.

Sulfur water:
Water containing objectionable amounts of hydrogen sulfide gas which causes an offensive "rotten egg" odor.

Suspended Solids:
Solid organic and inorganic particles that are held in suspension in a solution.

TDS:
Total Dissolved Solids- see dissolved solids.

TOC:
Total Organic Carbon- The amount of carbon bound in organic compounds in a water sample as determined by a standard laboratory test. CO2 is measured when a water sample is atomized in a combustion chamber.

Total Alkalinity:
(Sum of Carbonate and Bicarbonate, no MCL)
As a word, "alkalinity" means the opposite of acidity, but in water chemistry it is equal to the sum of the concentrations of carbonate (C03-2) and bicarbonate (HCO3-) ions, which act to stabilize, or "buffer" the pH of the water. Low TDS waters with less than 50 ppm (3 GPG) alkalinity are easily overwhelmed by acid rain and are often very corrosive. However, levels above 250 ppm (15 GPG) readily recombine with "hardness" ions (see Total Hardness) to form lime scale (calcium carbonate, CaCO3) in water-using equipment. Also, more than 150 ppm alkalinity interferes with flavor and carbonation in post mix beverages. Since both hardness and alkalinity come from limestone and then later may become lime scale, the concentrations of both are commonly reported as CaCO3" Drinking water supplies seldom exceed values of 300 ppm (18 GPG). The removal or reduction of alkalinity is called dealkalization, and it can be accomplished in several ways. One is simply to feed an acid or acidulate into the water to neutralize it. Ion exchange methods are also effective. The most extreme approach is to treat the water with a weak acid cation ("WAC") resin that is regenerated with acid (H+) instead of Na+ from salt (NaC1). In this process, much of the hardness is exchanged for H+, and the H+ then neutralizes one molecule of bicarbonate. Thus, both hardness and alkalinity are reduced, producing double the effect on scale.

Total Dissolved Solids (TDS):
(secondary MCL 500 ppm; 1,000 ppm in California)
TDS is an approximation of the amount of minerals dissolved in water. It used to be measured by evaporating a sample to dryness and weighing the residue, but that is a lot of trouble and not very precise. Now it is estimated electronically, by measuring the electrical conductivity. TDS is composed of not only hardness ions, but also such compounds as soluble iron, sulfates, dissolved silica, sodium and others. A TDS less than 50 indicates unusually "pure" water that is likely to be "aggressive" (corrosive); 150-300 ppm is average; 500 ppm is the recommended limit, beyond which there are often problems with taste, scaling, soft ice, even diarrhea. A TDS of 2000 ppm or more produces an osmotic pressure of at least 20 psi, thus requiring a pump to provide adequate water pressure for RO, which is the only reasonable remedy for such water. Remedies are limited to reverse osmosis and ion exchange processes.

Total Hardness:
(sum of Calcium + Magnesium, no MCL)
"Hardness" and "softness" of water are expressions of its tendency to make soap scum or soap suds, determined by the concentrations of calcium and magnesium in the water. Excess hardness is also often responsible for the curdling of cream and an unsightly scum on coffee and tea. (Other metal ions such as iron, zinc, copper, aluminum, etc. also contribute, but they are seldom present at significant levels). The Ca++ and Mg++ ion concentrations are measured separately and reported as mg/L Ca++ or Mg++. Then the two values are combined and converted mathematically into "grains per gallon as calcium carbonate" (GPG as CaCO3). Conversion factor 17.12 mg/L Ca++ plus Mg++ =1 GPG as CaCO3. Water with 3 GPG hardness or less is considered "soft" and non-scale forming; 3 to 10 GPG is a moderate scale former, not too troublesome; 10 to 15 GPG is hard and is a good scale former, causing lime scale problems where the water is heated or chilled; greater than 15 GPG is very hard water and a very good scale former which inevitably leads to serious maitenance problems. From 0 – 15 gpg, we recommend polyphosphate feed with fine filtration, from 15 -20 gpg, fine filtration blended with softening, over the 20 GPG range, we recommend reverse osmosis.

Total Organic Carbon (TOC):
(no MCL)
TOC is supposed to be a measure of most of the organic material that the test for Total Dissolved Solids misses. It includes the tannins, etc. from decaying vegetation that are responsible for “colour” in water, dissolved fragments of microorganisms and their by-products, and many pollutants, if present. “NPOC” means “Non-Purgeable Organic Carbon” and indicates that dissolved inorganic carbon dioxide, carbonic acid, carbonate, and bicarbonate were purged from the sample before analysis. Drinking water seldom exceeds 2.0 ppm, while levels above 2.0 ppm are considered high and levels above 5.0 are extremely high and are not usually observed. Activated carbon filters are efficient at removing TOC, but much of the colour of tannins can be physically removed by micro-filtration. The combination of lots of carbon and fine filtration is excellent for removal of TOC and colour.

Trihalomethanes (THM’s):
A group of organic chemicals, suspected of being carcinogenic, which are formed in water when chlorine being used as a disinfectant reacts with natural organic matter such as humic acids from decayed vegetation. Chloroform is one of the most common THM’s formed in this type of reaction. THM’s can be removed from water by contact time with GAC at a specified flow rate.

TS:
Total Solids- The sum of total dissolved solids and total suspended solids.

TSS:
Total Suspended Solids- The residual matter which can be removed from a solution by filtration.

Turbidity:
(MCL 1.0 TU)
Turbidity is cloudiness or haziness in water, caused by tiny particles of silt, clay, etc. that reflect and scatter light. Sometimes called “suspended solids,” turbidity particles are so small (less than a micron) that they never settle out due to gravity. U.S. regulations require that the turbidity be less than 1.0 TU at the time of disinfection, and most waterworks monitor it continuously. Turbidity is analyzed with a light meter set at a right angle to the light source and reported in “nephelometric turbidity units” (NTU of just TU). Up to 5 TU, very slight cloudiness; 20 TU, definitely cloudy; 100 TU, murky. Values of turbidity for drinking water usually fall within the range of 0 to 1 NTU. Levels from 1 to 5 NTU are considered high, and above 5 NTU extremely high and seldom encountered.

Ultra pure Water:
Highly- treated water of high resistivity and no organics; usually used in semiconductor and pharmaceutical industries.

Ultraviolet (UV):
Radiation having a wave length shorter than visible light but no longer than X-rays. Ultraviolet light with a wave length of 254 nm is used to kill bacteria and destroy ozone.

Unloading:
The release of contaminant that was originally captured by the filter medium.

Velocity:
Free air passing through a filter panel and measured in feet per minute (fpm). It is determined by the volume of air min (ft3/m) divided by the area of the panel (ft2). It is expressed in this case as ft/min divided by feet per minute (fpm).

Viscosity:
That property of fluids by which they offer resistance flow. Measured in poise, kinematic viscosity, centistokes, saybolt universal seconds (SUS), seconds saybolt, degree Engler and degree Barbey, Gardner – Holt, etc.

VOC:
Volatile organic compound – synthetic organic compounds which easily volatilize. Many are suspected carcinogens.

Voids:
The openings or pores in a filter medium.

Water (H2O):
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. The human body is approximately 70% water. An odorless, tasteless liquid that exists as ice in solid form and steam in vapor form. It freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit. It is called the universal solvent. It is a weak electrolyte and is only slightly compressible.

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 instantaneous pressures many times greater than normal pressures. For this reason, many building codes now require the installation of “water hammer arrestors” a device to absorb these shock waves and limit damage to appliances.

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.

Zinc:
(Zn+2, secondary MCL, 5 ppm)
The Zn++ ion occurs in drinking water only as a corrosion by-product from galvanized (zinc-coated) steel pipe or from fittings made of brass (a copped zinc alloy). Zinc is one of the few metals that are dissolved by strong base as well as by acid, and a water pH of 10 higher can produce a metallic, astringent taste, even a touch of nausea if left long enough. Zinc levels in drinking water seldom exceed 2.0 ppm, with levels on average reaching 0.08 ppm but usually lower.