Drinking Water Contaminants
Besides water, what might come out of your faucet

Introduction:
Since water is capable of dissolving or suspending a tremendous variety of materials there is simply no way to get "pure" water (H₂O and nothing but H₂O) out of your faucet. All water, outside of a research laboratory, will have some other stuff in it. Even distilled water you purchase in plastic bottles at the store will eventually have some carbon dioxide (CO₂) from the air dissolved in it forming a weak acid (carbonic acid), and worse, there will probably be some dissolved plastic molecules in it as well.  

I get a number of questions about the health effects of drinking distilled water, and you can read my response to the questions here.

Are all water contaminants bad for our health? Not at all. Many of the naturally occurring compounds in water are benign or even good for our health. Some minerals, like calcium and magnesium are essential to human health, and some reports indicate that drinking water can provide a dietary source for these minerals. Most of the discussion and links below will focus on the undesirable or dangerous water contaminants.  The environmental Protection Agency has established Maximum Contaminant Levels (MCLs) for some of the most common and/or potentially dangerous of the identified water pollutants.

The materials besides H₂O that might be in your drinking water can be categorized as shown below (only the most common or dangerous examples in each group are listed here, since there is a nearly infinite number of possible contaminants). This is a highly simplified list, but I did not want to get into a lot of chemistry and technical ideas and terms here. At some point I may create a page with more technical details for those who are interested, although anyone who is interested probably already knows far more than I do about the subject.

Please note:  The discussion below will focus on only a sample of the more common or dangerous contaminants.  These are not necessarily the contaminants that will be in your water (hopefully most will not be present).  Nor, as I mentioned, will this be a comprehensive list (some contaminants not mentioned below may, in fact, be in your water).  The only way to determine for sure what contaminants are in your water are to test for them. 

Where appropriate, in the lists of contaminants below, I have indicated in {MCL=} the Maximum Contaminant Level (MCL) established by the Environmental Protection Agency (EPA). The units are usually milligrams of the contaminant per liter of water.

  Materials dissolved in water:

Inorganic Compounds - Compounds that typically do not contain the element Carbon. They can become dissolved in water from natural sources or as the result of human activity.

	Dissolved gases (oxygen, carbon dioxide, nitrogen, radon, methane, hydrogen sulfide, etc.) - no appreciable health effects, except for hydrogen sulfide and dissolved radioactive gases like radon. Both methane and hydrogen sulfide can be inflammable. Carbon dioxide dissolved in water creates carbonic acid - a weak acid that gives carbonated water its "bite" and plays an important role in the weathering of limestone and other carbonate rocks. Caverns are a product of eons of erosion by carbonic acid laced water.
	Metal and metalloid positive ions - (aluminum, arsenic {MCL=0.05}, lead {MCL=0.015}, mercury {MCL=0.002}, calcium, magnesium, sodium, potassium, zinc, copper {MCL=1.3}, etc.) Some of these ions (lead, mercury, and arsenic) are dangerous at extremely low concentrations and can be introduced into drinking water either though natural processes or as a result of human activity. Other ions in this group (for example, calcium, magnesium, sodium, and potassium) are essential to human health - in the correct amounts. Calcium and magnesium are interesting ions. Although their presence in drinking water is actually a health benefit, they are the prime culprits in most hard water, and are considered undesirable contaminants by those who must live with scaly deposits of calcium carbonate on their faucets (and in their pipes and water heaters) or who can not get their soap to lather.
	Negative ions - (fluoride {MCL=4.0}, chloride, nitrate {MCL=10.0}, nitrite {MCL=1.0}, phosphate, sulfate, carbonate, cyanide {MCL=0.2}) As with the positive ions, some of these negative ions are necessary to life in proper concentrations (chloride and carbonate), others can be dangerous to health at moderate concentrations (nitrates and nitrites - look at the ingredients in the next slice of ham, bacon, or hot dog you eat), and others are dangerous at even small concentrations (cyanide). Some, like fluoride, have raised quite a controversy over its safety as an additive (in many areas) to drinking water in an effort to lessen tooth decay, particularly in children.
	Radon - Radon is a radioactive gas which comes from the natural breakdown (radioactive decay) of radium, which is itself a decay product of uranium.  The primary source of radon in homes is from the underlying soil and bedrock. However, an additional source could be the water supply, particularly if the house is served by a private well or a small community water system.

Organic Compounds - These compounds all contain the element Carbon. Although there are many exceptions, naturally occurring organic compounds (sugars, proteins, alcohol's, etc.) are synthesized in the cells of living organisms, or like raw petroleum and coal, formed by natural processes acting on the organic chemicals of once living organisms.

• Synthetic Organic Chemicals - Organic chemicals can also be synthesized in laboratories and by chemical companies. A growing number of these synthetic organic compounds are being produced. They can include pesticides used in agriculture, plastics, synthetic fabrics, dyes, gasoline additives like MTBE, solvents like carbon tetrachloride {MCL=0.005}, and many other chemicals. Many synthetic organic chemicals, like benzene {MCL=0.005} carbon tetrachloride, and vinyl chloride {MCL=0.002}, vaporize easily in air and are grouped under the category of volatile organic chemicals (VOCs). Methyl tertiary butyl ether (MTBE) is a common synthetic organic chemical used for a number of years as a gasoline additive. In January 2000 it received national notariety on CBS' 60 Minutes because of its ability to contaminate water supplies after leaking from storage tanks.
  The potential for water contamination by synthetic organic chemicals can be understood by the fact that Denver Water (the company that supplies municipal water to much of the metro Denver area) tests for 54 VOCs (21 with MCLs established by the EPA), 73 different pesticides (23 with MCLs), 25 different chemicals classified as synthetic organic compounds (5 with MCLs), and 7 as non-specific organics. Nearly all of these chemicals tested below the levels of detectability. It somewhat disconcerting to realize that Denver water tests for only 150 or so of the thousands of the synthetic organic chemicals manufactured, and the EPA has established MCLs for even fewer.
  As you read through the information in the sites listed in the "links" section, you will find that these are not nice chemicals to have in your water, many of them are presumed to increase the risk of various cancers in humans, often after many years of low-level exposure, others may affect the nervous system. Some researchers are reporting that yet other synthetic chemicals can cause hormonal disruptions. Most laboratory tests of the effects of these chemicals are done using a single chemical, but there may be several organic contaminants together in a water source. Scientists are just beginning to realize that exposure to multiple organic chemicals seems to increase the risk of health problems much more than any of the chemicals would separately.

Trihalomethanes {MCL=0.1} There is a class of organic compounds that is important because their formation and presence in drinking water is a direct result of the most common and economical process used to kill harmful pathogens, chlorination. This chemical group is the trihalomethanes (THMs). THMs are formed when the chlorine that is added to the water interacts with organic material also in the water, like leaf fragments, etc. The level of THMs in water is usually greater in water systems where surface water is the source, and levels typically vary seasonally with the organic content of the source water supply. Chloroform is usually the most common THM, and in Denver for instance, it varies from about 10 micrograms per liter in the winter to about 50 micrograms per liter in the summer with an average around 20-25 micrograms per liter. These levels are well below the EPA's Maximum Contaminant Level (MCL) of 100 micrograms per liter, but as you will see from some of the journal abstracts, referenced here even drinking water with THM levels below 100 microgram per liter over a 40-50 year period might increase the risk of certain cancers.  Evidence has also been reported that disinfection byproducts can cause adverse reproductive outcomes.

The graph above was created using published data from the The Santa Clara Valley Water District's Water Quality Laboratory reports for an eight month period in 1997. THMs were reported and graphed here as milligrams per liter.  The red line on the graph is the EPA MCL level of 0.10 milligram or 100 micrograms per liter. The intent here is not to imply that the water from this particular water treatment facility is bad, unsafe, or any worse than water from other facilities that chloronate surface water, in fact, like Denver Water, they produce a quatity product. I believe, though, that it is important to understand that a fairly large percentage of people in the United States and in other countries that chlorinate their water are drinking small quantities of chloroform and related substances on an ongoing basis.    

  Materials suspended in water: Of the extremely large number of things that can possibly be suspended in water, only those that are dangerous to health or that affect drinking water quality will be listed here.  If there are enough tiny particles suspended in water it becomes cloudy or turbid.  Light bounces off the suspended particles giving the water a milky or muddy appearance.  Gasses dissolved in water can also cause turbidity if they begin to come out of solution or "degas" (like the bubbles that form when a carbonated drink is opened).  Gas bubbles will eventually rise to the surface and disappear - the water will clear, other materials suspended in water neither rise nor settle, so the water does not clear.

Are you confused by the difference between a virus and bacteria? Ever wonder about emerging pathogens?  This article provides an overview on microbiology and provides a glimpse of a world we can’t even see.    

	Pathogens - disease causing organisms. I need to mention here that exposure to the disease causing organisms discussed below (E. coli, cryptosporieia, giardia, etc.) can come form sources other than one's drinking water. Exposure, for instance, can come from eating contaminated food, or from swimming in contaminated water, and sometimes by human contact. Viruses - Although, according the the EPA, most viruses transmitted in drinking water cause "gastrointestinal illness (e.g., diarrhea, vomiting, cramps)",  Viruses that cause  Hepatitis A and E can also be transmitted in un-disinfected drinking water.  It is fairly rare to read about specific disease outbreaks in the US and other developed countries that can be linked to viruses, in part because they are relatively difficult to detect, and in part because of the effective public water treatment systems in the country.  Bacteria - 100+ years ago cholera (caused by Vibrio cholera) and typhoid fever (caused by Salmonella typhi) were responsible for epidemics (caused by drinking contaminated water) that killed many thousands of people.  Today, in most parts of the world, because of chlorination and other water purification processes, we do not usually hear about cholera outbreaks unless an accident or natural disaster has disabled water  purification plants.  Today in the US,  the pathogenic bacterial contaminant most often encountered is fecal bacteria, or E. coli {MCL=0.0 bacteria}, which enters the water supply from human or animal wastes.  The EPA regulates the maximum allowable levels for this bacteria in drinking water, and most people most of the time either do not encounter these bacteria in their drinking water or do not get sick.  The article, Tap Water at Risk by the Houston Chronicle, reported that in the USA in 1994-1995, there were 3,641 water purification utilities  in the US that reported violating the federal health standards for fecal bacteria contamination. These utilities together served 11.9 million people. Despite these statistics, disease outbreaks (in people on municipal water) linked to E. coli in the U.S. appear to be quite rare. According to a note in the Denver Post (p. 4B), July 18, 1998 reporting that an E. coli outbreak that sickened at least 50 people in Alpine WY (population 470) was probably caused by a contaminated town water supply, the state epidemiologist said that it was only the second outbreak in the nation that has been linked to municipal water. Protozoans - Cryptosporidia and giardai {MCL=0.0 cysts}. These are one celled organisms, both of which form dormant cyst stages that are resistant to typical levels of chlorination, cause gastrointestinal disease, and are prevalent in the environment. According to EPA 811-F-96-007, May 1996: "Cryptosporidium has been found in nearly all surface waters that have been tested nationwide. As water systems monitor for Cryptosporidium, the likelihood exists that it will be detected occasionally at low levels in finished water derived from surface water sources. Cryptosporidium oocysts are very resistant to disinfection, and even a well-operated water system cannot ensure that drinking water will be completely free of this parasite." According to the Centers for Disease Control and Prevention: "Cryptosporidium parvum has been recognized as a human pathogen since 1976. In people with normally functioning immune systems, Cryptosporidiosis is manifested as an acute, self-limiting diarrheal illness lasting 7 to 14 days and it is often accompanied by nausea, abdominal cramps, and low-grade fever." For people with compromised immune systems an infection can be fatal.
	Asbestos - Asbestos {MCL=7 million fibers/liter} is a mineral that forms minute fibers in the environment.  You usually hear about exposure to airborn asbestos causing disease. Asbestos fibers can also be present in water, and it is regulated by the EPA because asbestos exposure from water has been linked to an increase in the risk of certain cancers.
	Other suspended solids - Unless the materials in the water are themselves dangerous (as discussed above, suspended solids are typically a nuisance rather than hazardous.  Suspended materials in the water, however, can interact with the disinfection processes making them less effective. Water professionals also use turbidity of the finished water as an indicator of its quality.  If the purification process is letting enough solids through that the water is cloudy, there is a chance that some of the "stuff" contributing to the turbidity is harmful.

To conclude the discussion on contaminants, you might find the opening exchange of Popular Science's exclusive interview (Oct. 1996) with Carol Browner, administrator of the U.S. Environmental Protection Agency, interesting  (The Popular Science web page was reorganized, and their "Water Report" from which this exchange was extracted was apparently deleted).

Popular Science: Why do Americans now buy so much bottled water?

Carol Browner: I think it's because of a lack of information, quite frankly. People have heard things, they're scared, and there's a product on their grocery store shelf. So it seems as if buying it is the way to get some information, the way to have some control over the situation.

What it also says to me is that the consumer is willing to make an investment in safe drinking water, and that we have to prove to them that investing in their tap water is what makes sense.

I would say that people in this country have every reason right now to ask questions. I wouldn't take for granted the safety of this nation's drinking water anymore. There's a series of problems from emerging threats like microbials. There's an infrastructure problem. We should just be honest about that. (emphasis mine)

PS: Could you comment further on this trend of people wanting to do things themselves, for example, buying bottle water instead of investing in the quality of their tap water?

CB: There is a lot of evidence that people have concerns and they want to do something themselves, whether it's buying bottled water or one of those filters to put on a water pitcher. I am very hopeful that the more we can provide people with information about what's actually being found in the source water and what actions are being taken to treat it, the more people will feel confident in their drinking water and have a greater willingness to invest in their local water system.

The Environmental Protection Agency (EPA) has several excellent sites that describe water contaminants.  The  EPA's Drinking Water Standards site gives you a list of the regulated contaminants, their maximum allowable contaminant levels, the main source(s) of the contaminants, and their health effects.  A more comprehensive EPA site is, What are the health effects of contaminants in drinking water?   Another excellent site for learning about the health effects of water contaminants is The National Environmental Education & Training Foundation (NEETF) site, 40 Fact Sheets for Common Drinking Water Contaminants.

If, after browsing the pages on this site, you have further questions, comments, new web pages to suggest, or if you are interested in information about drinking water filtration systems, please let me know.