ISSUED: 9-90
Joseph L. Taraba, Agricultural Engineering Department
Linda M. Heaton, Dept. of Human Environment: Design and Textiles Thomas W. Ilvento, Department of Rural Sociology

Many people judge the quality of water -- whether it is supplied by public or private water systems -- by its taste, odor and appearance. But the risk to one's health cannot always be judged by these factors. Many of the chemicals or biological organisms that affect health cannot be seen, tasted or smelled.
When consumers become concerned about the safety of their water supply, they may consider adding water treatment devices to their homes. The array of choices and the terminology associated with these devices can bewilder even the most knowledgeable consumer. This publication will assist a consumer in:
Determining whether a water treatment device is needed.
Understanding what the devices can remove from water and how they work.
Evaluating the effectiveness of a water treatment device for the home.

EPA Drinking Water Treatment Device Categories
The U.S. Environmental Protection Agency (EPA) has defined three general categories of filters for treating home drinking water: water filters, bacteriostatic water filters and water purifiers.
1.Water filters, generally comprised of activated carbon (AC), are intended to remove rust; sediment; organic compounds that impart taste, odor or color; chlorine and some other contaminants. They make no claims for pesticidal (antimicrobial) activity, and they are not designed to remove or destroy bacteria unless they are labeled water purifiers.
2.Bacteriostatic water filters, also comprised of AC, generally remove the same contaminants as water filters, but they are impregnated with an additional chemical agent, such as silver ions, that is intended to hinder the growth of bacteria trapped within the filter itself. (Bacteriostatic means the ability to inhibit the further growth of bacteria.) The label can then state "inhibits bacterial growth within the filter medium."
3.Water purifiers are designed to treat raw water of unknown microbial quality to make it suitable for human consumption. They must kill or remove essentially all bacteria, protozoa and protozoan cysts that the label or instructions claim to remove.
Water purifiers are further subdivided as pesticidal devices and pesticides. Consumers should not confuse the words pesticide and pesticidal with chemicals used in agriculture or households to control weeds, insects, molds or bacteria. Here the words mean an agent that destroys a pest. In this case the pest is human pathogen bacteria, protozoa and protozoan cysts.
(a)pesticidal devices purify water by physical or mechanical means, such as filtration, heating, etc. No antimicrobial chemical agent is involved.
(b)pesticides purify water through the use of antimicrobial agents (such as iodine) contained in the product.

Registering Treatment Devices
If a manufacturer claims that a unit will inhibit or reduce the growth of microorganisms, or kill or remove pathogenic organisms, and the unit contains a chemically active ingredient to promote the inhibition, the unit and the manufacturer are required to register with the EPA before the devices can be legally offered for sale. But if a unit does not contain a chemically active ingredient, then only the manufacturer must be registered. If a manufacturer makes no claims that the unit will inhibit or reduce microorganism growth, then neither the unit nor the manufacturer must be registered. The EPA registration does not imply any EPA approval of the unit nor its effectiveness for the manufacturer's stated purpose.

The registration means:
The manufacturer claims that the unit has some sort of pesticidal property.
Under normal use the pesticidal agent will not leach out of the unit in concentrations which would be harmful to humans.

The registration does not mean:
The unit is in any way endorsed or approved by EPA as a water treatment device.
The unit is in any way superior or inferior to any other unit.

Mechanical Water Filters
A mechanical water filter removes particulates by a mechanical process based on the physical size of the particulate. It can remove inorganic contaminants, such as heavy metals, if these inorganics or metals are in the particulate form and not dissolved in the water and if the particulate size is large enough for the filter medium to retain. It has been found that the total amount of some heavy metals, e.g. lead (Pb), copper (Cu) and cadmium (Cd) that are found in drinking water from taps in the household, is in both the dissolved and the particulate forms. The amount that is in the particulate form can vary from nearly zero to almost 100% of the total heavy metal present, and this undissolved part depends on the water pH, hardness, total dissolved solids, temperature, other inorganic and organic chemicals that are present and their concentrations.
Most heavy metals found in drinking water, particularly lead, rarely occur there naturally. They come most likely from the water distribution system or from brass fittings, faucets or household plumbing that is copper with lead solder.
Mechanical filters include depth filters and surface filters. A depth filter consists of an array of fibrous, granular or sintered material that is wound, pressed or bonded together, with openings of decreasing size.
A consumer would choose a depth filter when particulate loads are high (i.e., when there are visible and settleable particles) or when there is a need to filter out a large amount of particulates without clogging the filter.
Surface filters trap sediment at or very near the material surface. Included in this category are filters made of membrane, pressed fiber and ceramic-coated or resin-bonded filters. They function like a screen, and precision openings in the filter can be manufactured. A specific opening size (e.g., 0.3 microns) can be made to filter out bacteria, protozoa, spores and cysts. These will remain trapped on the surface of the filter. These filters cannot screen out viral particles because a virus can be as small as 0.01 microns.
Surface filters have an advantage over depth filters because the size of the retained particle can be defined more precisely, but they clog more readily than depth filters. Usually they are preceded by a depth filter.

Activated Carbon Water Filters
The majority of water filters purchased today contain activated carbon or charcoal (AC). The AC may be powder, granules, solid block, paper membrane or wound spool made of carbon-impregnated cotton cord or foam. Some devices contain AC but make no claim that it is present. Literature for some devices claim to remove odor and taste without mentioning AC. The only way the consumer can determine its presence may be to break open the device, thus destroying its effectiveness.

Activated Carbon Types
AC is a form of carbon that is modified by a carefully controlled oxidation process to develop a porous carbon structure with a large surface area. Some of the raw materials from which AC is made are coal, bones, wood, nut shells, peat, lignite, residue from petroleum processes or other organic materials. The oxidation process can produce two distinct types of AC:
L-carbon (L-AC) which is formed by oxidation at 300° - 400°C (570° - 750°F) with air or an oxidation chemical and
H-carbon (H-AC) that is produced in a cooking process at 800° -1000°C (1470° - 1830°F) and cooled in an inert atmosphere.
L-AC has the ability to adsorb dissolved alkaline heavy metal ions such as Pb+2, Cu+2, Cd+2, Hg+2 depending on certain operational parameters such as pH and total dissolved solids. L-AC has acidic surface characteristics that interact with the basic metals. L-AC can be regenerated using a strong acid to remove the adsorbed metal ions in a process similar to regeneration of ion exchange resins used in the water softening process by the use of salt (NaCl) or an acid.
One comprehensive study has shown that lead can be reduced to less than 1 ppb for typical water passing through a household plumbing system using AC and mechanical filtration. Much research has been conducted using AC to reduce heavy metals, but these studies have not documented reductions of heavy metals to the maximum health level concentrations that are typically a few ppb.
The EPA has set heavy metal maximum concentrations which are listed in Table 1 (effective November 1989).
NOTE: Many of these concentrations are subject to review, and new concentration levels may be established. Updated concentrations can be obtained through your local health department, public water system or your local Cooperative Extension office.

Table 1. Drinking Water Standards for Heavy Metals (EPA, 1989)
Heavy Metal MCL*(ppb)
Arsenic 50
Barium 1000
Cadmium 10
Chromium 50
Lead 50
Mercury 2
Selenium 10
Silver 50
*Maximum Contaminant Level -- statutory maximum concentration allowed for public water supplies by EPA. Subject to change in the future

H-AC has alkaline surfaces that do not effectively attract the alkaline heavy metal ions in solution in the water. The surface characteristics of H-AC make them more efficient absorbers of organic chemicals, particularly those that are hydrophobic, i.e., those chemicals that have very low solubility in water. The ability of H-AC to adsorb heavy metal ions from solutions seems to be increased with acid-washed H-AC which neutralizes the alkalinity of this AC while not significantly reducing the ability to adsorb organic chemicals. Heavy metal ions that are complexed with synthetic or natural organic compounds, i.e., chelated ions, have shown to be effectively removed from water by unmodified H-AC due to AC's ability to adsorb the organic chelating compound.

How Activated Carbon Structure Works to Filter Water
A lattice of internal microscopic passages formed during the oxidation process gives AC an immense surface area. A single gram of AC can have a total surface area of more than 1,000 sq. ft. AC is extremely adsorptive. It can effectively remove organic compounds, chlorine and dissolved radon. Carbon filters will not remove bacteria, calcium and magnesium (hard water), fluorides, nitrates, chlorides and many other inorganic chemicals. Heavy metals can be adsorbed onto AC by only a very specific type AC.
The molecules that are removed diffuse into the AC pores and eventually stick to the internal surfaces (see Figure 1). All compounds are not adsorbed onto the AC surface equally. Smaller molecules will diffuse deeper into AC and can adsorb on more surface area than large molecules because of the size of the pores. Organic chemicals which are the least soluble in water (high molecular weight, low polarity, less ionic) have greater adsorption onto the AC.
AC's effectiveness to remove organic compounds decreases with increased temperature and AC absorptivity is reduced. Particulate and bacteria growing on the AC may clog the pores.
The number and kind of compounds in the water will affect AC's ability to remove compounds. A compound with a higher affinity for adsorption on AC may displace a compound already adsorbed. When an AC filter is nearly saturated with compounds, those compounds with a low affinity for AC may not be adsorbed at all.
A parallel can be seen in the water softening process using ion exchange resins. The resins are recharged by passing a high concentration of sodium (Na+) ions over the resin bed replacing the magnesium (Mg2+) and calcium (Ca2+) ions in the resins because the Na+ has a higher affinity when it is at very high concentration. When Na+ is at a low concentration in hard raw water, the Mg2+ and Ca2+ ions have a higher affinity on the exchange resin and take the place of the Na+ ion on the resin.
The organic material used and how it is processed to AC (see Activated Carbon Types) affect both its ability to adsorb chemicals and its total removal capacity.

Activated Carbon Filter Types
Four types of AC filters are marketed as home treatment devices (see Figure 2A & 2B, Figure 2C & 2D).
1.Faucet filters: These slip over the mouth of the water faucet. Two basic designs are the bypass and the no-bypass:
*bypass: has a valve that allows you to filter only the water used for cooking and drinking (prolongs the life of the filter).
*no-bypass: filters all the water flowing through the faucet.
2.Pour-throughs: These are the simplest and most portable. They require no installation at all. The user simply holds the filter over a container and pours in tap water.
3.In-line or stationary: Tapped into the cold-water pipe, these filter all the water flowing through the pipe.
4.Line bypass: These are installed by cutting into the water line beneath the sink. A separate faucet attached to the sink delivers filtered water for drinking and cooking, but unfiltered water can still be drawn from the regular faucet.

Factors Affecting AC Filter Performance
The following factors seem to affect the performance of AC filters, and consumers should investigate them before choosing an AC filter:
1.water contact time with AC
2.iodine number
3.particle size of the AC
4. manufacturer's recommended water volume treatment capacity
5.tests and ratings of independent organizations

Contact Time. This is the time it takes water to flow through the device. Contact times can vary from one second to two minutes. The longer the contact time, the more chance for the chemicals to diffuse into the AC to be adsorbed.
The more AC in a device seems to indicate more treatment capability if the flow rate of water (e.g., gallons per minute) is the same. Table 2 lists the contact times for a few home AC filters.
Iodine number. One measure of AC's capacity to remove organics is the iodine number. This is the amount of iodine, in milligrams, adsorbed by one gram of AC at a standard set of conditions. The higher the iodine number, the more adsorptive the AC. It is rare to see such a number reported in the advertising literature or instructions or on box labels of AC devices. Table 2 gives the iodine number for a limited number of AC filters.
Particle Size. The smaller the particle size, the more outside surface is available for compounds to enter the internal porous matrix of the AC, resulting in a higher removal rate of organic contaminants. Therefore, powdered AC and block AC, made from compressed powdered AC, would be more effective than granulated AC if the AC had the same iodine number, AC amount and contact time.
Recommended Capacity. Some manufacturers of AC water treatment devices give a recommended water treatment capacity in gallons. When the rated capacity is exceeded, they recommend replacing the AC.
Most devices on the market do not indicate how much water has passed through the filter during use. A consumer can estimate the number of days a filter will last before needing replacement. Assume that each person uses one gallon of water each day for drinking and one to three gallons a day for cooking. For a household of four people who would use one gallon per person per day, four gallons of water will need to be treated daily. At this rate of use, an AC treatment device with a 200-gallon capacity will last approximately 50 days (200 gal./4 gal. per day).

Table 2. Performance Factors and Removal Efficiency for Selected AC.
rated capacity 
Amount of 
of carbon
Contact time 
Average % 
of THM
Average % 
Average % 
Removal of 
Line bypass
Culligan SG-2 4,000 1,708 980 39 89 28 99
Aquacell Bacteriostatic 2,000 417 876 13 86 23 97
Aqualux CB-2 2,000 1,150 966 35 98 23 99
Everpure QC4-THM 1,000 765 1,010 43 99 55 99
Seagull IV 1,600 300 434 15 70 41 97
Hurley Town & Country 4,000 895 913 36 69 31 97
Aqua Guad ACT31 500 51 1,275 3 43 12
Instapure F1-C 200 27 1.6 24 11
AMF Cuno-IM 3,000 395 870 3.6 34 7
Filbrook 1,000 97 788 44 40 14 94
Source: GSRI Study for EPA, 1984.

Performance of Activated Carbon Filters
Performance of AC filters has been reported by Consumer Reports (Jan. 1990 and Nov. 1983), Rodale's Practical Homeowner (Jan. 1987), EPA from results of tests conducted by Gulf South Research Institute (GSRI) in J. American Waterworks Assoc. (April 1984) and National Sanitation Foundation (NSF) (address: 3475 Plymouth Road, P.O. Box 1468, Ann Arbor, MI 48106, telephone number: 313-769-8010).
The results summarized below are for a limited number of AC devices to illustrate their performance differences. Table 2 lists a number of AC treatment devices from the GSRI study, and Table 3 summarizes AC filters tested by Consumer Reports and NSF. GSRI tested for the removal of these organic compounds:
trihalomethanes (THMs): chloroform, bromoform, dichlorobromomethane, and dibromochloromethane) which are primarily byproducts of chlorination disinfection of drinking wafer
NPTOC (nonpurgeable total organic carbon) which is predominated by larger molecules whose origins are natural organics that can cause "off" taste, odor and color in water and
halogenated hydrocarbons (carbon tetrachloride, trichloroethylene, tetrachloroethylene, trichloroethlane, dichlorobenzene, hexachlorobenzene and chlordane) whose origins are industrial solvents.

Table 2 summarizes the percent removal of each of these three categories during the manufacturer's rated filter life. Figures 3 and 4 illustrate the removal efficiency of THMs and NPTOCs as the filter processes water. In all examples the removal efficiency decreases as increased volume of water is processed. Substantial differences do occur. Polycyclic aromatic hydrocarbons (PAHs) have been removed by AC at efficiencies comparable to PCBs and halogenated hydrocarbons.
Consumer Reports (Jan. 1990) states that high treatment capacity AC filters (>1,000 gal. capacity) are more effective than other type AC filters, such as faucet-mounted or pour-through types (see Figures 2A and 2B) when chloroform (a THM) removal was tested.
Rodale Press analyzed AC treatment devices and published results for chlorine and halogenated organics (72 of EPA's 129 priority pollutants, the tested organics not defined). These results are listed in Figures 5 and 6 for the rated filter life capacity. The percentage removal of halogenated organics was the total removed and does not differentiate between specific chemicals. No chemical-specific removal percentages were listed.

Table 3. Activated Carbon Filters -- Cost Comparisons.
Manufacturer Model Cost Replace Filter
Cost (each)
Filter Rated 
Capacity (gal.) 
Removal (%)
High Volume Filters
Ametek CCF-201 $158 $20 (2 req'd) 1500 >97
Amway E-9230 276 69 5000 >97
Culligan Supergard
349 37 1000 90
Cuno Aqua Pure
155 15 450 90
Everpure H200 298 90 750 >97
Filterite CF-10 85 8 750 90
Kinetico MAC 275 32 500 90
NSA Bacteriostatic
179 5000 80
Omni UC-2 99 20 (2 req'd) 80
Cuno PPO11O5 $30 $6 735 60
Pollenex WP90K 22 5 200 30
Brita $30 $8 35 65
Innova 7 5 30 45
Glacier Pure 13 5 100 40
Source: Consumer Reports (Jan. 1990) and National Sanitation Foundation.

(Figure 3)

(Figure 4)

(Figure 5)

(Figure 6)

Validation of Performance Claims
The National Sanitation Foundation (NSF) validates manufacturers' claims if they voluntarily submit their units for testing and if their devices meet NSF standards for the specific compound the manufacturer claims to remove.
The NSF tests treatment devices under two separate standards (#42 and #43): 1 ) chemicals that affect only the aesthetics of drinking water (i.e., taste, odor, color and appearance) and 2) hazardous chemicals.
The devices tested for aesthetics are challenged with a standard prepared water (chemical components exceeded the recommended concentrations of EPA's Secondary Drinking Water Standards) to substantiate claims. The effluent from these units must meet the EPA Secondary Drinking Water Regulations while processing the water up to the device's rated capacity. The devices must be periodically tested to certify that they continue to meet claims.
NSF also established Standard #43 for assessing and certifying drinking water treatment devices that claim to reduce hazardous chemicals in drinking water (i.e., those chemicals that exceed the EPA Primary Drinking Water Standards or those chemicals that are suspected to cause illness but for which there is no EPA standard).
The NSF requires that the manufacturers of tested equipment provide a means (possibly an indicator or warning) to alert the consumer when the unit is not performing properly. These may be on the device (e.g., an automatic shut-off, a reduction in flow, an alarm) or in a separate test kit provided to the consumer. If these are not provided, then the AC filter must meet the removal efficiency of Standard #43 for twice the rated filter capacity. This gives a safety factor to the consumer.
NSF also evaluates under Standard #42 bacteriostatic devices designed to limit the passage and/or growth of heterotrophic bacteria. It requires that the bacterial population is no greater in the effluent from the device than in the influent. NSF tests whether the active bacteriostatic agent or its degradation product in all effluent samples exceeds the EPA Primary Drinking Water Regulations or those of any other federal regulatory agency for chemicals not regulated by EPA.
Devices meeting NSF's standards are allowed to display the NSF Mark (see Figure 7) on the device, literature and advertising. Twice a year NSF publishes a list of those devices currently meeting their standards.

Radon Gas Removal
Scientists know that AC can remove 99 percent of radon gas dissolved in water, but they have not yet established efficiency rates for radon removal for commercially available drinking water treatment devices.

Bacterial Growth on Activated Carbon
AC units have several drawbacks. Because AC deactivates it, chlorine cannot disinfect bacteria present in the AC. However, if water is pretreated to eliminate pathogenic bacteria before it reaches the device, these bacteria do not grow and multiply on the AC.
But non-pathogenic bacteria, in particular heterotrophic plate count (HPC) bacteria, will grow. The health effects of high counts of HPC bacteria are not clear. We take in millions of bacteria a day, normally with no ill effects, and a healthy person is generally not at risk. But there may be a potential health risk for those who are more vulnerable, such as the aged, the very young or the sick whose immune systems are weaker. Certain HPC bacteria are known to be "opportunistic" and may take advantage of these weaknesses and cause illness.
A high bacterial count can occur when water does not pass through an AC filter after it has not been used overnight. The first water drawn from the filter that day may be cloudy with bacteria. Flushing the filter at full flow for 30 seconds reduces the HPC bacteria counts to 1/7 the initial numbers, and as the AC filter is used during normal household activity for four hours, the HPC bacteria are reduced by 1/25. Still, several studies indicate that the HPC bacteria count is higher in effluent than in influent.
One promoted solution may be a bacteriostatic filter. The AC in bacteriostatic filters is impregnated with silver to prevent HPC bacterial accumulations. The silver is a disinfectant, and when released or leached from the AC in small quantities, it interacts with the bacteria in the filter and reduces their ability to multiply. The silver, a heavy metal, should be released in small enough quantities so as not to exceed the toxic limits set forth by the EPA Primary Drinking Water Regulations.
Studies by the GSRI for the EPA have indicated that silver-impregnated AC made little difference when compared to untreated AC in terms of HPC bacteria growing on the AC or in total counts found in the effluent water. The only advantage noted in several studies of silver-impregnated AC was that in the first month of use, the bacterial counts were lower than AC without silver.
The best recommendation for preventing high HPC bacteria counts is to replace the AC filter periodically at least as often as the manufacturer recommends or even more frequently. If the manufacturer makes no recommendation, replace the AC at least every six months (maybe even every three months) even if the manufacturer's recommended treatment capacity is not exceeded. Otherwise, the owner should adhere strictly to the manufacturer's recommendations for changing the filter's AC.

When An AC Filter Is No Longer Effective
Another disadvantage of an AC filter is that the only way to be sure the filter has reduced the contaminants of concern is to test the water coming out of the filter unless the manufacturer provides a testing procedure. The consumer will be aware of the loss of effectiveness because of an "off" taste, odor or color in the water. If the contaminant affects only the aesthetics of the water, then the filter's ineffectiveness does not pose a health risk. But many hazardous chemicals cannot be detected by taste, odor or color.

Recommendations to the Consumer
Use AC filters to treat water only for drinking and cooking unless radon removal is required.
Use AC filters on water that is disinfected before it reaches the filter.
Use AC filters on cold water only.
Replace the filter:
- if signs of sediment appear in treated water.
- if taste, odor or color changes. This can mean that the A C is no longer effectively removing the compounds.
- when the flow is noticeably reduced.

Filter the water at the slowest possible rate tolerable to increase contact time.
Flush filters for 30 seconds when first used each day. Flush the filter for two or three minutes if not used for several days.
Change the AC filter:
- as frequently as the manufacturer recommends ~ preferably more often. If there is no manufacturer's recommendation, change the filter every three months even if the water treatment capacity is not exceeded.
- when treatment capacity is reached. Estimate use at one gallon of water per person per day for drinking and two gallons per person per day for drinking and cooking.

Select AC fillers whose claims are independently validated by a nationally recognized independent testing laboratory.
Silver-impregnated filters reduce bacteria on filters for up to four weeks, then give similar results as other AC filters.

This material is based on work supported by the U.S. Department of Agriculture, Extension Service, under special project number 89-FWQI-1-9156.
Trade names are used for comparison purposes only. No endorsement is intended, nor is criticism implied of similar products not named.

Water Quality Terms
Activated carbon or activated charcoal (AC) -- Particles or granules of carbon produced by carbonization of cellulosic or other organic matter in limited or no air. These particles possess a very porous structure that has highly adsorptive properties to remove some organic and inorganic contaminants and certain dissolved gases from water.
Aesthetic quality -- The quality of water as sensed by sight, taste and smell. These quality standards are usually referred to in drinking water quality standards as secondary or other contaminants that do not have a direct health impact.
Adsorption -- The process by which a gas, vapor, dissolved material or a minute particle adheres to the surface of a solid.
Bacteriostatic -- The ability to inhibit the further growth of bacteria.
Contamination -- Any introduction into water of microorganisms or chemicals in a concentration that makes water unfit for its intended use.
Chelated ion -- An ion, usually a metal, that is in close combination with an inorganic or organic compound that keeps the ion dissolved and prevents it from exhibiting its usual properties, e.g., forming a solid that settles.
Cooking process -- Carbonization process of organic material in the absence of air at high temperature.
Contact time -- The time it takes for water to flow through a treatment device.
Deactivate -- Reduction in the ability of a solid surface to adsorb chemicals. An action causing pathogenic organisms to lose their ability to cause disease.
Disinfection -- The removal or destruction of infectious or pathogenic microorganisms (bacteria, virus or protozoa).
Drinking water treatment unit (DWTU) -- A device used to improve the quality of water for its effects on aesthetics and human health and to make it suitable for drinking.
Effluent -- The water that flows out of a DWTU.
Hardness -- A measure of the minerals, predominantly calcium and magnesium, dissolved in water that affect its soap neutralizing characteristics and the formation of scale on pipes and in boilers.
Heavy metal(s) -- One or more of the following metals whose density is greater than 5 gm/cc: cadmium (Cd), lead (Pb), mercury (Hg), copper (Cu), silver (Ag), zinc (Zn), chromium (Cr), barium (Ba), arsenic (As), selenium (Se).
Heterotrophic bacteria -- Bacteria that thrive only on organic matter for energy and growth.
Hydrophobic -- Lacking the affinity for, repelling or failing to be absorbed by water.
Influent -- The water entering a DWTU.
Inorganic compound -- A substance that does not contain carbon (except as carbonates, cyanates, cyanides, or carbide).
Maximum contaminant level (MCL) -- A standard that is the highest allowable concentration of a contaminant in drinking water. This standard is set as a result of scientific studies of contaminant effects on health or aesthetics.
Mechanical filter -- A device that removes particulates, sediments or colloidal material from water by physical size as the water passes through a medium made of a screen, fibrous, granular or sintered material that is wound, pressed or bonded together.
Micron -- A unit of measure that equals 0.000039 inches (abbreviated as 1 m) is a micrometer (1 x 10.6 meter).
Microorganism -- A microscopic organism, including bacteria, protozoa, yeasts, viruses and algae.
Nonpurgeable total organic carbon (NPTOC) -- Usually relates to large organic molecules whose origins are natural and that impart taste, odor and color to water. These compounds are not in general related to health risks.
Pathogen -- Any microorganism which may cause a disease.
Pesticide -- An agent that destroys a pest. In water, a pest generally refers to human pathogenic bacteria, protozoa or protozoan cysts or viruses.
pH -- The strength of the acid or base present measured on a scale of 0 to 14 with a pH of 0 to 7 being an acid, pH of 7 being neutral and a pH of 7 to 14 being a base.
Point of entry treatment (POE) -- Treatment of water at the entry point to a home or business.
Point of use treatment (POU) -- Treatment of water at the point of use, such as a kitchen tap.
Polychlorinated biphenyls (PCBs) -- A group of man-made chemicals made up of two benzene rings bonded together (biphenyl) with one or more hydrogen atoms replaced by chlorine. PCBs have been used in electrical equipment, hydraulic fluid, inks, paints, adhesives, fire retardants and heat transfer fluids. They have been banned for most uses since 1979.
Polycyclic aromatic hydrocarbons (PAHs) -- Also known as polynuclear aromatic hydrocarbons (PNAs) formed during incomplete combustion of fuels (coal and petroleum products) and cellulosic material (wood, paper, tobacco). They are multiringed hydrocarbon compounds (aromatics) that share two or more carbon atoms by two or more rings. Many compounds in this group are carcinogenic.
ppb -- Parts per billion. The number of weight or volume units of a minor constituent present with one billion units of a major constituent of a mixture.
ppm -- Parts per million. The number of weight or volume units of a minor constituent present with one million units of the major constituent of a mixture.
Primary drinking water standards -- Standards for maximum contaminant limits (MCL) of pollutants in drinking water that affect human health. These standards are set by the EPA to be met by public water systems.
Public water system -- Any system owned by any person for the provision to the public of piped water for human consumption if the system has at least 15 service connections or serves regularly an average of at least 25 individuals daily at least 60 days a year.
Purification -- The removal of objectionable matter from water by natural or artificial methods.
Radon -- A radioactive gas that is a natural radioactive decay product of uranium.
Regenerate -- A process used to restore the adsorption activity of a substance.
Secondary drinking water standards -- Standards for maximum contaminant levels (MCL) in drinking water that affect aesthetics (taste, odor, color and corrosivity) but do not pose a health risk. These standards are encouraged by EPA but not enforced except if alternate water sources have comparable costs and have lower secondary concentrations.
Sediment -- Suspended solid particles that settle from water.
Solubility -- The extent to which one substance will dissolve in another substance.
Trihalomethanes (THMs) -- A group of chemical organic substances that contain halogen elements (i.e., chlorine, fluorine, bromine, etc.) attached to three positions on a methane molecule. These compounds are derived from many sources and are toxic when found in more than trace amounts. THMs are a by-product of the chlorinated process to disinfect water when organic compounds are present.
Validate -- To confirm or verify that claims made are correct based on a standard or standard method.

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