Water (H2O) can dissolve or suspend many substances: those that are beneficial to health and those that are actively harmful.
	All drinking water, whether it is from a municipal supplier, a private source (well, spring, lake, etc.) or a bottled water provider will contain some contaminants, and the contaminant levels and types can change over time.
	Regulations in developed countries ensure that municipal water is treated to reduce levels of the most common and harmful contaminants to levels that are as safe as possible within cost constraints and the necessity of moving the treated water through miles of pipes.  Overall, municipal tap water in developed countries is safe for the vast majority of citizens and has saved countless lives over the alternative of drinking untreated water.  Levels of harmful contaminants that remain after treatment (or are added during treatment) may increase the risk of health problems for a very small number of individuals who drink the treated tap water.
	Certain elements of the population, young children, pregnant women and the elderly and immunocompromized,  may be more susceptible to harm by water contaminants than the rest of the population.
	Everyone will have different levels of comfort with the contaminants that are found in their drinking water - whether the water is from a private or a municipal company - or from a well or private source.
	Once you understand the contaminants that are (or might be) in your drinking water and properties of the various treatment methods, you will be able to make an informed decision (based on your comfort level) whether to drink your untreated tap water or invest in a treatment method to raise your water quality.  Hopefully your decisions will be based on knowledge, understanding and critical thinking, and they will not be a reaction to proclamations of some scare-monger or scam artist trying to sell you a product you may not need or that would not be effective.

Water has been called the universal solvent because so many substances will dissolve in it.  Water also can carry many materials in suspension.  Unfortunately, water is not particularly selective in which compounds become dissolved or suspended.  The water that dissolves your coffee or tea and sugar in the morning or that you use to reconstitute your orange juice or infant's formula might also have dissolved some atoms of lead from the pipes in your home or picked up a microgram of 2,4 D from the farm upstream from the filtration plant.  If your water is chlorinated it almost certainly contains a few micrograms of chloroform (a byproduct of the disinfection process).

The question you need to ask is not, "does my tap water contain contaminants" - all water outside of laboratory distilled, deionized water does.  The real questions are, "what are the contaminates in my water, what are their concentration levels, and do they pose short or long term health risks at those levels."

Finding answers to these questions may not be easy.  The answers depend on where you live (country, city, surrounding land use, etc.), the primary source of your drinking water (confined or unconfined aquifer or surface water), your water supplier (private or community well, small or large municipal water system), and what is happening at any moment as your water travels from its source through the treatment/distribution system to your faucet.

Water that is reasonably contaminant free (and safe) one moment can become dangerously contaminated the next because of accident, neglect, or some natural event.  One of the most notorious recent examples of water that was safe one day and dangerous the next was during the summer of 1993 in Milwaukee when one-fourth of the people living in the metro area (over 400,000) became ill with cryptosporidiosis.  According to the 1996 Houston Chronicle series, Tapwater at Risk, the contamination of Milwaukee's water supply was a combination of natural events (heavy rains) and accident (improperly installed monitoring equipment) that allowed the parasite to pass though the city's purification system and into the distribution system.  In August of 1998 the citizens of Sydney Australia were told that Cryptosporidia had been detected in their municipal water supply.  Fortunately, despite a two-day delay in informing the population, there were apparently no reported cases of death or illness linked to the contamination.

Most government entities and water providers are extremely committed to supplying safe water to their citizens and/or customers.  Consequently, barring accidents, the majority of dangerous contaminants that are liable to be in the drinking water of most Americans (and people from other developed countries) are typically present in minute amounts.  They may contribute to health problems for some only after many years of exposure, making identification of the cause difficult, if not impossible.  Examples of this type of contaminant are low levels of lead (usually dissolved out of distribution pipes or plumbing fixtures in the home) which causes intellectual deficits in children, and trihalomethanes (a byproducts of chlorine disinfection) that have been linked to a slight, but significant, increase in the chance of getting certain cancers after 20 - 50 years of drinking chlorinated water.

Water treatment is not a simple issue.  It is, rather, a delicate balancing act.  There are ongoing and vigorous debates among the various groups interested in drinking water safety concerning the costs, the benefits, and the risks of every aspect of the water treatment and distribution business.  Anything that is done to treat municipal water costs money, provides the benefit of water that has reduced levels of the targeted contaminants, and decreases risk of disease from the targeted contaminants.  The treatment process may also add substances to the water that would increases risks of other disease for a few people who drink the water.

I suspect that in your reading you will find that in the United States and other countries, there are many committed people who are doing  a good job to ensure that the water delivered to your home is safe for drinking.  These are scientists who are trying to figure out the effects of various chemicals and pathogens on the human body or discover better treatment technologies, government regulators who try to identify, monitor, and regulate the amount of certain contaminants allowed in water, and professionals in the water industry who strive to deliver safe, quality water to their customers.

You will also discover that 'the system' does not always work.  Accidents happen, mistakes are made, systems wear out, toxic chemicals are released into the environment to find their way into the surface and ground water, regulators fail to regulate, population growth in a region puts more stress on a water system than it can handle, and any number of other weak links in the chain of processes that must function properly to deliver safe water to your faucet.  In February 2011 celebrity physician, Dr. Mehmet Oz, aired a series entitled, How Safe Is Your Drinking Water (Parts 1, 2, 3, 4 can be viewed online - the 4th episode discusses fluoridation).

So, are there reasons to be concerned about your drinking water safety?  Your answer to that question must depend on the results of your own research and your own tolerance for risk.  The site links listed below and information in the other pages at this site contain a tremendous amount of information on water quality.  You might also want to contact your water provider and obtain a "Treated Water Quality Summary Report" (The Water Quality Reports from Denver Water are a good example of what to request.  If you use well water you should have your water tested periodically to make certain that it does not contain significant levels of harmful contaminants.

From everything I have read, people in the US who have the most reasons to be concerned about their water are those served by small water treatment plants - particularly in agricultural regions of the country or areas with a number of industrial plants.  Also, anyone using water from a shallow well should keep a close eye on their water's quality - again, the most common areas of concern would be in agricultural or industrial areas.  This is, of course, not to say that all small water treatment plants or shallow wells will have contaminated water.  Nor does it mean that all water from large municipal treatment plants or deep wells will be free of harmful contaminant.  The Environmental Protection Agency's Safe drinking water information system will allow you to locate your drinking water supplier and view its violations and enforcement history since 1993.

Am I concerned about the quality and safety of my tap water?  Mildly concerned, yes --- Panicked, no.  I live in Denver, Colorado, and my family and I use municipal water supplied by Denver Water.  The taste of their water is excellent (hardly a taste of residual chlorine) and all of the harmful chemicals for which they test fall well below the Environmental Protection Agency Maximum Contaminant Level (or MCL) (most are below the levels of detection).  Despite the good taste and safe test results of our water, my research into drinking water issues convinced me to purchase a high quality water filter for the following reasons:

• I do not like the idea of me or my family drinking even a little bit of chloroform on a daily daily basis over the course of a lifetime (the chlorination of Denver water produces between 8 and 53 micrograms of chloroform per liter of water - these levels are produced by nearly any treatment facility that adds chlorine disinfectant to surface water).  Disinfection byproducts are a fairly easy contaminant to remove.
• We live in an old house (pre 1950), and I was concerned about lead in the pipe solder and plumbing fixtures possibly leaching into the water.  It is estimated that over half of the homes in Denver have some lead plumbing, and reports regularly indicate at least several thousand individuals and families in any given year are expected to be exposed to lead levels in their drinking water above the EPA action level of 15 parts per billion.  I actually purchased a lead-test kit when I started researching water quality in 1996, but our purchase of a water filter certified to remove lead made testing the water irrelevant, and the kit is still sitting around somewhere unused.  You don't have to constantly worry about your drinking water quality and safety if you,
  (a) know which contaminants are liable to be in your drinking water, and
  (b) invest in a high quality treatment system that's certified to remove the contaminants you are concerned about.
• I wanted to ensure the safety of my family in the event of some accident in the water purification/distribution system even though chances of a problem are remote.
• Even good quality municipal water tastes much better with the residual chlorine or chloramines removed.
• I figured that with contaminants constantly increasing in our environment, removing one of the potential sources of harmful chemicals or disease causing organisms was something positive that I could do very easily for my family even if the risks of actual harm were extremely low.  The information that I read about possible effects of contaminants on children and pregnancy was particularly sobering.

Risks to: Children | Pregnant Women | Elderly and/or Immunocompromised

Children and the Risks of Contaminated Water:
The following excerpt from a report entitled Just Add Water from the Environmental Working Group by Brian A. Cohen, Richard Wiles, Erik D. Olson, and Chris Campbell, should help families recognize the importance of drinking pure, contaminant free water.

• Drinking water standards have many other shortcomings beyond their failure to regulate common drinking water contaminants such as radon, Cryptosporidium and pesticides like cyanazine.  One of the most serious is the fact that most current federal drinking water standards do not make any specific accommodation for the special risks and heavy consumption of water by infants and young children.
  
• One-year-olds drink more than twice as much water relative to their size as adults.  Measured in terms of total fluid intake, an adult would have to drink 35 cans of soda per day to match the drinking habits of the average one-year-old.  Because of this, infants and young children are exposed to more water-borne contaminants, relative to their size, than adults. (emphasis mine)  This higher exposure combined with the increased vulnerability of infants to many chemical and microbiological contaminants, means infants and young children face increased risks from virtually all contaminants in drinking water, and that current standards almost always do not provide adequate protections for this vulnerable portion of the population.
  
• In October of 1995, the EPA announced a new policy to protect infants and children from exposure to toxic substances.  At that time, EPA Administrator Carol Browner noted that the policy:
  "...will, for the first time, ensure that we consistently and explicitly evaluate environmental health risks of infants and children in all risk assessments, risk characterizations, and environmental and public health standards that we set for the nation." (EPA 1995)
• In justifying the need for this new policy the EPA cited two National Academy of Sciences studies (NRC 1993, NRC 1994) that called for major policy changes at the EPA to integrate explicit protections for children when evaluating health risks from environmental contaminants.
  
• To date, just two (lead and nitrate) of the more than eighty drinking water standards have been set explicitly to protect infants and children from immediate or long term health risk.  No standards have been modified since the EPA policy was announced.
  
• Similarly, drinking water standards do not account for multiple contaminants in a single glass of water.  Instead, they are set as though people are exposed to one contaminant at a time, which very often is not the case.

(End of excerpt)

Specific Water Contaminants of Concern for Children:
National Resources Defense Council - Our Children At Risk
EPA - Children and Drinking Water Standards - includes list of Contaminants to Which Children May Be Particularly Sensitive 

• Lead - Discussed in detail here.
   
• Nitrates - A common pollutant in water in the Midwest or other agricultural regions.  High levels of nitrites or nitrates in the water supply can interfere with infants' ability to absorb oxygen and can lead to "blue-baby" syndrome (methemoglobinemia), which can result in death. EPA has set drinking water standards for nitrates and nitrites.
   
• Pesticides - Malignancies {in children} linked to pesticides in case reports or case-control studies include leukemia, neuroblastoma, Wilms' tumor, soft-tissue sarcoma, Ewing's sarcoma, non-Hodgkin's lymphoma, and cancers of the brain, colorectum, and testes.  Although these studies have been limited by nonspecific pesticide exposure information, small numbers of exposed subjects, and the potential for case-response bias, it is noteworthy that many of the reported increased risks are of greater magnitude than those observed in studies of pesticide-exposed adults, suggesting that children may be particularly sensitive to the carcinogenic effects of pesticides.  Zahm SH, Ward MH., Pesticides and childhood cancer, in Environ Health, in Perspect 1998 Jun;106 Suppl 3:893-908.  
  A related article,  Cancer Risk and Parental Pesticide Application in Children of Agricultural...
   
• Biological Contaminants - E. coli, giardia and cryptosporidia cysts can all cause gastro-intestinal problems where dehydration from diarrhea and vomiting may be more severe and rapid than in adults.  These contaminants can cause death.  In 1998, EPA established the Interim Enhanced Surface Water Treatment Rule, which strengthens control over microbial contaminants, including the pathogen, Cryptosporidium. By 2002, public water systems using surface water (or ground water under the direct influence of surface water) and serving more than 10,000 peopl must comply with the rule. States must adopt the new standards by 2001.  In some people, particularly children under 5 years of age and the elderly, E. coli 0157:H7 infection can also cause a  complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail. About 2% of infections lead to this complication.
   
• Disinfection Byproducts (DBPs) - According to the EPA, the risk varies depending on the DBP.  Some epidemiological studies may indicate a link between certain DBPs and a slight increased risk of reproductive and developmental effects.  
  • It would make sense that if drinking water contaminated with moderate levels of DBPs over a lifetime increases the risk of some cancers, it would be an excellent idea to remove as many of these compounds from the drinking water as soon in life as possible and continue the removal through adulthood - even if the risk were very low.

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Specific Water Contaminants of Concern During Pregnancy:

• Disinfection Byproducts - 
  A 1998 Federal Register report, National Primary Drinking Water Regulations, Disinfectants and Disinfection Byproducts Notice of Data Availability, listed several studies that suggested pregnant women who drank water containing teh disinfection byproducts, Trihalomethanes (THM) could increase the risk of neural tube defects in the developing fetus or early term miscarriage.  A 2002 review of research to date, concluded "The present study indicates that exposure to chlorinated surface waters with a high content of natural organic matter increases the risk of birth defects.  ...The present findings also suggest that natural organic matter in nonchlorinated tap water contains substances that may increase the risk of congenital birth defects."  However, a more recent review in 2009 concluded, "Although some individual studies have suggested an association between chlorination disinfection by-products and congenital anomalies, meta-analyses of all currently available studies demonstrate little evidence of such an association."

  Although a number of studies in the 1990s seemed to implicate disinfection byproducts as causing a slight increase in risk of miscarriage and a number of birth defects, subsequent research seems to show less evidence that exposure to normal levels of disinfection byproducts will cause significant increases in rates of miscarriages and birth defects.  This information has been retained, however, to illustrate how scientific knowledge advances - and the current conclusions are still subject to change.  

  • Neural tube defects - "The authors reported elevated odds ratios (ORs), generally between 1.5 and 2.1, for the association of neural tube defects with trihalomethanes (THMs). However, the only statistically significant results were seen when the analysis was isolated to those subjects with the highest THM exposures (greater than 40 parts per billion {or ppb}) and limited to those subjects with neural tube defects in which there were no other malformations (odds ratio = 2.1, meaning that the odds of a pregnancy with neural tube defects were about double what they would have been without exposure to THMs)."  Several recent  papers have supported the 1998 findings:  Dodds L, King WD., Relation between trihalomethane compounds and birth defect, in Occup Environ Med 2001 Jul;58(7): 443-6; Nieuwenhuijsen MJ. et. al., Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review, in Occup Environ Med 2000 Feb;57(2):73-85;  Klotz JB, Pyrch LA., Neural tube defects and drinking water disinfection by-products, in Epidemiology 1999 Jul;10(4):383-90
  • Miscarriages - "Women with high THM exposure in home tap water (drinking five or more glasses per day of cold home tap water containing at least 75 micro gram (ug) per liter of THM) had an early term miscarriage rate of 15.7%, compared with a rate of 9.5% among women with low THM exposure (drinking less than 5 glasses per day of cold home tap water or drinking any amount of tap water containing less than 75 ug per liter of THM - {or 75 parts ppb})."  A more recent 2006 review, however, concluded, "These results provide some assurance that drinking water DBPs in the range commonly encountered in the United States do not affect fetal survival."

  • It is worth mentioning that the current EPA Maximum Contaminant Level (MCL) for total THMs is 80ug/l (or ppb).  A link to Some medical abstracts concerning pregnancy and disinfection  byproducts.

  • Do not drink water that has not been disinfected or cut back your water intake in an effort to reduce THM or other contaminant exposure.  Based on the current state of knowledge, any potential risks of adverse pregnancy outcomes associated with drinking water containing THMs are far lower than the risks of serious illness and death that could result from consuming drinking water that has not been properly disinfected.  If you want to reduce exposure to THMs consider drinking bottled water from a NSF certified company or purchasing a treatment system (discussed elsewhere) that is certified by NSF to remove THMs.

There are ongoing studies that implicate a variety of other drinking water contaminants as possibly causing problems with pregnancy or the developing fetus:

• Arsenic: A 2013 article on arsenic in drinking water and food states, "Long famed for its homicidal toxicity at high doses, a number of studies suggest that arsenic is an astonishingly versatile poison, able to do damage even at low doses.  Chronic low-dose exposure has been implicated not only in respiratory problems in children and adults, but in cardiovascular disease, diabetes and cancers of the skin, bladder and lung."
• Nitrates: Higher water nitrate intake was associated with several birth defects in
      offspring, but did not strengthen associations between nitrosatable drugs and birth defects.
• Other organic compounds like Dioxin have also been implicated as having harmful effects on
      the developing fetus. another article, Dioxin fact sheet.
• Lead: Discussed in detail here.

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Risks to the Elderly and/or Immunocompromised:

• Although both populations are affected by all of the contaminants listed above, they are at special risk of serious injury or death from biological, pathogenic contaminants.  If there is any chance that their drinking water has been contaminated with harmful bacteria, or cysts, their drinking water should be disinfected immediately (boiling would be a good option), or they should drink a good quality of bottled water until the water is safe.
   
• In some people, particularly children under 5 years of age and the elderly, an E. coli 0157:H7 infection can also cause a complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail.

Water Treatment Suggestion for High Risk Groups

• If there are members of these high-risk groups living in your home, it would be an excellent plan to & consider investing in a permanent high quality water treatment strategy, since:
  • There is always a "lag time" (up to 24 hours) between the discovery of pathogens or other harmful contaminants in a municipal water supply and issuing an 'Emergency Boil' or 'Do Not Drink' notification' to the public - Without continuous protection there is always a small risk that your normally safe water will become contaminated and used before you received notification.
  • There are disinfection byproducts at some level in nearly all water that is chlorinated.  The highest levels are usually found in chlorinated water (municipal or private) from a surface source or water from an unconfined aquifer.  Water from confined aquifers typically does not have to be chlorinated as heavily (if at all) as water from the other sources.  This water also usually contains a lower level of the organic material (leaf fragments, etc.) that interacts with chlorine to form the disinfection byproducts than does surface water or water from an unconfined aquifer.
  • Some older homes have the potential for lead to leach into the drinking water from the plumbing pipes and fixtures - this problem is discussed in detail on the previous page.
  • In agricultural regions, there is a good reason to expect nitrate, pesticide, and possibly bacterial contamination, particularly in private wells using water from unconfined aquifers (or in surface water).  Surface water is also likely to contain cryptosporidia or giardia cysts.  Wells in these regions should be tested, and water quality reports should be studied carefully to see if these contaminants exist in the drinking water.

• In my experience, the most simple and economical long-term solution to reduce the majority of the contaminants (except nitrates and chronic bacterial or viral contamination) commonly found in municipal water to safe levels is a NSF certified, high-quality, Solid Block, Activated Carbon (SBAC) filtration system with a  sub-micron pore size.
  • These systems will significantly reduce the chlorine, DBPs, cysts, asbestos, and a wide range of pesticides and other organic contaminants from your drinking and cooking water.  Most SBAC filtration systems also remove lead effectively, and some are designed to remove mercury, but check with the manufacturer to make certain.
  • Although these filters are not recommended for continual use with bacterially contaminated water, the pore size is small enough to reduce the levels of many types of bacteria that might accidentally contaminate a normally safe water supply.  NSF does not certify filtration systems for bacterial removal, however water suspected of containing pathogens can be treated with UV or ozone after filtration.
• If nitrates, arsenic other heavy metals or salts are known (or suspected) to be in the water, in addition to the contaminants listed above, a high-quality, Reverse Osmosis (RO) system would be the most economical long-term solution.  Any RO system you purchase should have a good activated carbon solid block post-filtration system to remove any contaminants not removed by the RO membranes.  As with carbon filtration, water suspected of containing pathogens should also be treated with UV or ozone.
• Distillation is also an excellent method for treating water containing contaminants that are not removed by activated carbon, but it is typically more expensive than reverse osmosis and requires energy to heat the water.

It is possible, though thankfully rare, for harmful bacteria or other pathogens to find their way into drinking water from a municipal water source. If these organisms are in the water illness can occur.  If tap water is regularly suspected to contain harmful pathogens, there are several point of use treatment options that can be considered for home drinking water if on a municipal water system.

Distillation and ozone are probably more expensive options than filtration and UV treatment.

If you are on on a well and suspect (or have found) biological contamination, point of entry disinfection might be the most economical solution for bacterial or viral contamination.

Bottled water is a good emergency source of safe drinking water, but often, by the time a problem has been discovered and the 'emergency boil' or 'do not drink' order has been issued, many people have already been exposed to the contaminated water.  A better solution when you suspect that municipal water (or well water for that matter) is or may become unsafe, is to install and maintain a permanent treatment system for all water consumed in the home (including tooth brushing).  Individual-size bottles can be carefully cleaned and filled with the treated water to drink away from home.