Descriptions of Common Contaminants (by category)
Hundreds of contaminants can occur in drinking water. They can be grouped into four basic categories: microbial, inorganic, organic, and radiological. Although there are over 100 contaminants that can be found in drinking water many of these contaminants are very rare. The following sections briefly discuss 40 of the most common contaminants in drinking water. These contaminants are listed alphabetically within the four categories.
Microbial Contaminants
Microbial contaminants include bacteria, viruses, and protozoans. These are living organisms that are visible in water only with the help of a high-powered microscope. Many different kinds of bacteria, some disease causing, may be present in a water supply. The tests discussed below are specific bacteria tests used to determine whether disease-causing bacteria may be present in the water. Protozoans are less common in water than bacteria, but a few can be problems. Viruses will not be discussed because they are expensive and difficult to test, however, viruses such as hepatitis are carried by water and can cause serious illness.
Coliform Bacteria
Coliform bacteria are a large group of bacteria that occur throughout the environment. They are used as an indicator organism to indicate the potential for disease-causing bacteria to be present in water. In other words, if coliform bacteria are present, it is presumed that a contamination pathway exists between the bacteria source and the water supply and disease-causing bacteria may use this pathway to enter the water supply. Most coliform bacteria do not cause disease, but the greater their number the greater the likelihood that disease-causing bacteria may be present. Since coliform bacteria stay in water longer than most disease-causing organisms, the absence of coliform bacteria leads to the assumption that the water supply is microbiologically safe to drink. Consuming water with coliform bacteria present may cause gastrointestinal illnesses, fever, and other flu-like symptoms. Therefore, the drinking water standard requires that no coliform bacteria be present in public drinking water supplies. Results from coliform bacteria tests are normally expressed as “Present” (P), or “Absent” (A). In this case, “Present,” indicates only that at least one bacterium was present in each 100 ml of water.
Fecal Coliform Bacteria
Fecal coliform bacteria are a smaller group of bacteria within the coliform bacteria group. Fecal coliform bacteria are specific to the intestinal tracts of warm-blooded animals. If the total coliform test is positive, the lab tests the water sample for fecal coliform bacteria. Fecal coliform bacteria levels are expressed as the number of colonies per 100 ml of water. No fecal coliform bacteria are permitted in public drinking water supplies.
E. Coli
An even more specific bacteria test is the test for E. coli (short for Escherichia coli). This is a type of fecal coliform bacteria commonly found in the intestines of animals and humans. A positive E. coli result is a strong indication that human sewage or animal waste has contaminated the water.
Hundreds of strains of E. coli exist. Although most are harmless and live in the intestines of healthy humans and animals, a few can produce a powerful toxin that causes severe illness and even death. Infection often causes severe bloody diarrhea and abdominal cramps; sometimes the infection causes non-bloody diarrhea. Frequently, no fever is present. It should be noted that these symptoms are common to a variety of diseases and may be caused by sources other than contaminated drinking water. E. coli tests are reported as the number of bacteria per 100 ml of water. The presence of any E. coli in a water sample is unacceptable; thus, the primary drinking water standard for E. coli is 0 per 100 ml of water.
Standard Plate Count (Heterotrophic Plate Count)
The Standard Plate Count (SPC) or Heterotrophic Plate Count (HPC) is a more general indicator of bacterial contamination. On some test reports, this also may be referred to as the “Total Bacteria Count.” It measures all the bacteria, including coliform and many other groups, in a water sample. The SPC is usually reported as the number of bacteria per milliliter of sample. There are no drinking water standards for SPC, but if more than 500 bacteria are counted in one milliliter of sample, further testing for total coliform or fecal coliform bacteria is suggested.
Iron Bacteria
Iron bacteria are a type of bacteria that feed on small amounts of iron in water. Iron bacteria are not a health threat, but are a nuisance because they form strands, masses, or thin films that plug pipes, toilets, and plumbing fixtures and reduce flow from wells. Their appearance can vary from orange or brown to clear. Iron bacteria can colonize an entire water system from the well itself through the plumbing, or they may be present only in parts of the plumbing system. There are no drinking water standards for iron bacteria. Rather, their presence is normally enough of an aesthetic problem to require treatment. Water testing is rarely available to determine if iron bacteria are present. Confirmation is usually based upon the visual symptoms in the water.
Giardia and Cryptosporidium
Giardia lamblia and Cryptosporidium parvum are small microscopic animals known as protozoa. They both can live in the intestinal tract of mammals, including humans. While there, they multiply by producing oocysts. Infected animals and humans can excrete the oocysts, which can then contaminate water sources. Both giardiasis and cryptosporidiosis cause severe diarrhea, nausea, fever, headache, vomiting, and loss of appetite. Both illnesses can be life-threatening to people with depressed immune systems. Most outbreaks have occurred in communities that use surface water supplies (streams, rivers, lakes) where the oocysts can commonly be found. Shallow springs or poorly constructed wells that become contaminated with surface water could also contain Giardia and Cryptosporidium oocysts. Both Giardia and Cryptosporidium are measured in water by passing large volumes of the water through a small filter and examining the filter under a microscope for oocysts. Oocysts should be totally absent for water to be safe to drink.
Inorganic Chemicals (IOCs)
The second category of water contaminants includes inorganic chemicals. These are usually substances of mineral origin. Salt, metals, and minerals are examples of inorganic chemicals. The chemicals discussed alphabetically below are the most common inorganic contaminants in water supplies, or they are of the greatest health concern.
Arsenic (As)
Arsenic occurs in groundwater from both natural sources and human activities, like runoff from orchards or glass and electronics production wastes. In drinking water, it is odorless and tasteless. Arsenic has a primary drinking water stadnard because it can cause skin lesions, circulatory problems, and nervous system disorders. Prolonged exposure also can cause various forms of cancer. The present arsenic drinking water standard is 10 ug/L (0.010 mg/L).
Chloride (Cl)Typically the concentration of chloride ions in water is used to identify saltwater intrusion. Chloride has a secondary drinking water standard of 250 mg/L because it may cause a salty taste in the water.
Copper (Cu)
Copper usually originates from corrosion of copper plumbing in the home (see “Corrosivity,” below). Copper causes a bitter, metallic taste in water and a blue-green stain in sinks and bathtubs. Copper levels above 1.3 mg/L are a health concern because they may cause severe stomach cramps and intestinal illnesses. Copper can be reduced in water using the corrosion control strategies outlined below.
Corrosivity
Corrosive water is a term used to describe aggressive water that can dissolve materials with which it comes in contact. It is a problem because many homes have copper or galvanized pipes, lead solder joints, and brass plumbing fixtures. Thus, corrosive water may cause increases in copper and lead concentrations in drinking water. Symptoms of corrosive water problems include metallic taste, bluish-green stains in sinks and bathtubs, and, in severe cases, small leaks in the plumbing system. Because corrosive water is not a health concern by itself, there is only a secondary standard that water be noncorrosive.
Iron (Fe)
Iron is a common natural problem in groundwater and has a secondary drinking water standard of 0.3 mg/L. Iron does not cause health concerns but causes aesthetic problems such as metallic tastes and orange-brown stains.
Lead (Pb)
If lead is detected in your drinking water, it probably originated from corrosion of your plumbing system. Lead was a common component of solders used in plumbing systems until it was banned in 1991. If your home was built before 1991 and has a metal plumbing system, it is likely some lead is present. If your water supply is corrosive (see discussion above), any lead present in the plumbing system may be dissolved into your drinking water. Lead concentrations are usually highest in the first water out of the tap (known as “first-draw” water), since this water has been in contact with the plumbing for a longer time. Lead concentrations typically decrease as water is flushed through the plumbing system. Lead poses a serious health threat to the safety of drinking water. It is colorless, odorless, and tasteless. Long-term exposure to lead concentrations in excess of the drinking water standard has been linked to many health effects in adults including cancer, stroke, and high blood pressure. At even greater risk are the fetus and infants up to four years of age, whose rapidly growing bodies absorb lead more quickly and efficiently. Lead can cause premature birth, reduced birth weight, seizures, behavioral disorders, brain damage, and lowered IQ in children. The U.S. Environmental Protection Agency considers lead to be the most serious environmental health hazard for children in the United States.
In rare cases, the source of lead in drinking water might be from groundwater pollution rather than corrosion of the plumbing system. Such pollution may be the result of industrial or landfill contamination of groundwater. The source of the lead usually can be determined by comparing water test results from a first-draw sample versus a sample collected after the water runs for several minutes. If the lead concentration is high in both samples, the source of the lead is likely from groundwater contamination.
Manganese (Mn)
Like iron, manganese is a naturally occurring metal. It has a secondary drinking water standard of 0.05 mg/L. Manganese does not cause health concerns but causes aesthetic problems such as objectionable tastes or blackish water stains.
Nitrate (NO3) or Nitrate Nitrogen (NO3-N)
Nitrate in drinking water usually originates from fertilizers or from animal or human wastes. Nitrate concentrations in water tend to be highest in areas of intensive agriculture or where there are many septic systems. Nitrate has a primary drinking water standard that was established to protect the most sensitive individuals in the population (infants under 12 months of age, pregnant women, and people with certain blood disorders). These segments of the population are prone to methemoglobinemia (blue baby disease) when consuming water with high nitrate. Nitrate may be reported on your water test report as either nitrate (NO3) or nitratenitrogen (NO3-N). Look carefully at your report to determine which form of nitrate is being reported. The primary drinking water standard or MCL is 10 mg/L as nitratenitrogen(NO3-N).
Turbidity
Drinking water should be sparkling clear for health and aesthetic reasons. Turbidity refers to fine particles of clay, silt, sand, organic matter, or other material that might reduce the clarity of water. Turbidity makes water unappealing to drink because of its muddy appearance. Particles may also shield disease-causing bacteria from chlorine or other treatment and provide nutrients for bacteria and viruses to flourish. Turbidity usually indicates direct pollution from surface runoff often during or shortly after heavy rainfall. Turbidity is usually measured in a special unit known as an NTU or Nephelometric Turbidity Unit. The standard for turbidity depends on the type of water treatment technology used. Water treatment plants using conventional or direct filtration are required to have less than or equal to 0.3 NTU in at least 95% of measurements taken each month. Slow sand and diatomaceous earth filtration plants are required not to exceed 1 NTU in at least 95% of measurements. Water with more than 1 NTU of turbidity makes disinfection to kill bacteria difficult.
Organic Chemicals
Organic chemicals are a group of over 100 mostly man-made chemicals. They can occur in drinking water sources from industrial activity, landfills, gas stations, or pesticide use. Many organic chemicals are carcinogenic (cancer causing), so they often have very low drinking water standards, usually measured in ug/L.
Generally, organic chemicals are grouped into two major categories: volatile organic chemicals (VOCs) and synthetic organic chemicals (SOCs). The discussion below introduces these two groups and describes in detail the most common examples in each group;Volatile Organic Chemicals (VOCs)
VOCs are man-made compounds that are released from water into the air. They present a health risk not only from drinking contaminated water, but also from inhaling VOCs that escape from the water as it is used during showering or other home uses. VOCs also are absorbed directly through the skin during bathing and showering. They are commonly used as solvents, fuels, paints, or degreasers. Virtually all VOCs produce an odor in water, although it may not be obvious before the drinking water standard is exceeded. Nearly all VOCs have primary drinking water standards, because they cause cancer or damage to the liver, kidneys, nervous system, or circulatory system. Dozens of VOCs are regulated in public water supplies, but the most common are described below.
Benzene
Benzene is a clear, colorless liquid used primarily as an industrial solvent. It is lighter than water, migrates easily in groundwater, and is slow to decay. It is also present as a gasoline additive. Because it is a known human carcinogen (causes cancer), benzene has a primary drinking water standard of 0.005 mg/L (5 ug/L).
Carbon TetrachlorideCarbon tetrachloride is a colorless liquid that is heavier than water but migrates easily in groundwater. It has been used mostly in the dry-cleaning industry. Carbon tetrachloride has a primary drinking water standard of 0.005 mg/L (5 ug/L because it is a probable human carcinogen with other acute effects on the gastrointestinal and nervous systems.
Tetrachloroethylene (PCE) and Trichloroethylene (TCE)
Tetrachloroethylene (commonly known as PCE) and Trichloroethylene (commonly known as TCE) are similar chemicals that have been found around industrial sites and landfills. Most of the groundwater contamination from these chemicals occurred due to improper disposal of industrial wastes. Both chemicals are used as industrial solvents. PCE is used primarily in the dry-cleaning industry. Both are heavier than water and move freely through soil and groundwater. PCE is a possible carcinogen that causes liver, kidney, and nervous system damage. TCE is a probable carcinogen that also causes acute effects to the liver, kidneys, and central nervous system. Both PCE and TCE have primary drinking water standars of 0.005 mg/L (5 ug/L).
XylenesXylenes are a component of gasoline. They also are used in the manufacturing of some chemicals, and therefore appear commonly in industrial wastes. Xylenes cause liver, kidney, and nervous system damage. Xylenes biodegrade and move slowly in groundwater. The drinking water standard for xylenes is 10 mg/L (10.000 ug/L).
Nonvolatile or Synthetic Organic Chemicals (SOCs)Nonvolatile organic chemicals are also known as Synthetic Organic Chemicals or SOCs. Nearly all SOCs are pesticides, with a few notable exceptions (PCBs and dioxin). They differ from VOCs because they do not escape readily into the air from water.
Atrazine
Atrazine is water-soluble and moves easily into groundwater and surface water after application. Because it is classified as a possible human carcinogen that also damages the liver, kidney, and heart. Atrazine has a primary drinking water standard of 0.003 mg/L (3 ug/L).
.
Simazine
Simazine is commonly used for control of broad-leaved and grassy weeds on crops, orchards, and Christmas tree farms. It is also used to control plants and algae in ponds and lakes. Simazine has a primary drinking water standard of 0.004 mg/L (4 ug/L) because it is a probable carcinogen that also can cause damage to the testes, kidneys, liver, and thyroid after long exposure. Simazine travels easily through soils to groundwater and persist in groundwater for long periods of time.
2,4-D
2,4-D is commonly used to control broad-leaf weeds in agriculture and woody plants along roadsides, railways, and utility rights-of-way. It has been most widely used on wheat and corn, and on pasture and rangelands. 2,4-D has a primary drinking water standardof 0.07 mg/L (70 ug/L) because ti can cause damage to kidneys, liver, or adrenal glands. 2,4-D is readily degraded by microbes located in soil and water. Leachng to groundwater may occur in coarse-grained sandy soils with low organic content.
2,4, 5-TP (Silvex)
2,4,5-TP, banned since 1985, was used as an herbicide to control woody plants, and broadleaf weeds in rice, bluegrass turf, in rangeland improvement programs, and on lawns. Aquatic uses included control of weeds in ditches, riverbanks, on floodways, along canals, reservoirs, and streams. The primary drinking water standard is 0.05 mg/L (50 ug/L) because it has the potential to cause liver and kidney damage.
Picloram
Picloram is commonly used to control weeds such as bitterweed, knapweek, leafy spurge, locoweed, larkspur, mesquite, prickly pear, and snakeweed. Picloram has a primary drinking water standard of 0.5 mg/L (500 ug/L) because it can cause liver damage. Picloram does not adhere to soil and so it can leach to groundwater.
Radionuclides
Radioactivity usually occurs in water from radium, uranium, or radon. These materials emit radioactivity as alpha, beta, or gamma radiation. Each form of radiation affects the human body differently, yet all can lead to cancer. Radioactivity in water is normally measured in picocuries per liter (pCi/L).