Water dissolves or suspends many substances (contaminants), and almost any water you drink will contain some contaminates.   -  Dissolved substances include inorganic and organic molecules   -  Suspended substances include silt, protozoa, algae, bacteria and viruses
	Water Contaminants can be beneficial nutrients or harmful to health, and some can be nuisances.  The amount of many contaminants dissolved or suspended in water often determines whether they are harmful, beneficial or a nuisance.  Copper, selenium, zinc and many other minerals, for example, are essential to health in small amounts, but toxic in greater amounts.  Some contaminants have no known health benefits and are harmful when absorbed (i.e. lead and mercury).
	Municipal (public) water providers are required to test the treated water on a regular basis to ensure that regulated harmful contaminants are below levels considered to have significant adverse health effects, and most are required to distribute annual water quality reports to their customers.
	Your water's source can help you understand what contaminants might be in your drinking water. - Municipal water is treated to reduce regulated contaminants to levels that are considered relatively safe. - Private water supplies (particularly from the surface and shallow wells in unconfined aquifers) can contain any number and type of contaminants, and the only way to know what is in your water is with regular tests.
	Nearby industrial and agricultural activities can contaminate drinking water sources.
	Chlorination and other disinfectants kill pathogens but introduce traces of contaminants (disinfection byproducts) that carry their own health risks which are minimal at regulated levels.
	The age of a home or other building can help determine contaminants that might be introduced into drinking water from the plumbing.
	No treatment method is 100% effective at removing contaminants (distillation is close), and all treatment methods, whether by a municipal water company or home treatments, have associated costs and limitations.
	Link to additional resources:  -  Comparison of Drinking Water Treatment Methods  -  Some water contaminants (but not all that are harmful) can be identified by taste, odor &/or smell.  -  Relative Size of Pathogens and Filter Pores  -  Comparison of Long-Term Costs for Water Treatment

Water is called the Universal Solvent since it dissolves more substances than any other solvent.  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 make at home or purchase at the store will eventually have some carbon dioxide (CO₂) from the air dissolved in it forming a weak acid (carbonic acid).  Distilled water bottled in plastic will probably contain some dissolved plastic molecules in it as well.  

I get a number of questions about possible 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 although most people obtain most of their minerals from food, 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.  While some contaminants are always harmful to health (lead, mercury and arsenic, for example), some can be beneficial at low to moderate levels and harmful or a nuisance at higher levels (for example, calcium, magnesium and fluorine).

The materials besides H₂O that might be in your drinking water can be categorized as shown below.  This is a highly simplified list, but I did not want to get into a lot of chemistry and technical ideas and terms here.

Please note:  This discussion will focus on only a sample of the more common or dangerous water contaminants, since there is a nearly infinite number of possible contaminants.  These are not necessarily the contaminants that will be in your water (hopefully most will not be present).  There may also be harmful contaminants not mentioned in this discussion that are actually in your drinking 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 U.S. Environmental Protection Agency (EPA).  The units are usually milligrams of the contaminant per liter of water.  The MCL is the maximum concentration of a chemical that is allowed in public drinking water systems. Currently there are fewer than 100 chemicals for which an MCL has been established; however, these represent chemicals that are believed to pose the most significant risk.

Materials dissolved in water:
Dissolved substances are usually individual atoms, molecules or ions (molecules that have gained or lost one or more electrons).  Water solutions are mixtures of atoms, molecules &/or ions (the solute) uniformly distributed in water (the solvent).  Life (as we know it) could not exist without these aqueous solutions - they transport food and oxygen from the digestive system to individual cells and waste products out of the cells and create the environment within cells for all chemical reactions of life.  Everyone drinks water, and as a consequence is exposed to any substances that are dissolved in it - beneficial &/or harmful.

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.) - most have 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, in part, a product of eons of erosion by carbonic acid laced water. 

• Metal and metalloid positive ions - (aluminum, arsenic {MCL=0.05}, iron, 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 the fluoride ion, have raised quite a controversy over its safety as an additive to drinking water (in many areas) in an effort to lessen tooth decay, particularly in children.
   
• 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.   
   
• Carbon dioxide is a gas normally found in the atmosphere that readily dissolves in water to form carbonic acid and lowering the pH.  Water with a low pH can corrode metal pipes causing contamination.

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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 notoriety 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.
  
  These are not good chemicals to have in your water, and 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 classified under disinfection byproducts 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 quality 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.  Although individual health risks are quite small, the presence of THMs in our drinking water, and the possibility that our water might also contain traces of other synthetic organic chemicals, was one of the reasons I decided to purchase an activated carbon water filtration system - it was an easy way to remove those concerns.

Materials suspended in water:
Water molecules are in constant motion - hurtling around ricocheting off each other and any other substances that might be in it.  Small organic, inorganic or living particles keep getting knocked around in random directions by these water molecules, and if they are small enough, this motion is enough to keep gravity from pulling them down and they remain in suspension - like a never ending soccer game with no goals.  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.  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. 
 

• 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, from swimming in contaminated water, from human contact, from breathing contaminated air, etc.

  	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 1996 series of articles, 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.
  	Protozoa - 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, however, an infection can be fatal.

  
  Are you confused by the difference between Protozoa, bacteria, algae and viruses?  Ever wonder about emerging pathogens?  This article provides an overview on microbiology and provides a glimpse of a world we can�t even see.   
   
• Algae - Algae (or phytoplankton) are a type of aquatic plant (has chlorophyll and are capable of photosynthesis).  They are free-floating and have no roots.  There are a number of types of algae including the blue-green algae, and they form the foundation of both fresh and salt water ecosystems - they turn the sun's energy into food for a number of different types of animal life. 
   
• Asbestos - Asbestos {MCL=7 million fibers/liter} is a mineral that forms minute fibers in the environment.  You usually hear {MCL=7 million fibers/liter} is a mineral that forms minute fibers in the environment.  You usually hear about exposure to airborne 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.

Quality Reports & Testing |  Location  |  Disinfection Byproducts  |  Lead  |  Sensory Clues to Contaminants
 

Although water companies in the US and many other countries are strictly regulated and the treated water must meet certain minimum purity and safety standards, all water companies are not created equal.  You can reasonably assume that most are doing the best they can with the resources available to them - if for no other reason than to keep their name out of the evening news. in general, though, the larger water companies (in the US anyway) have greater resources available to treat and distribute the water and maintain the distribution infrastructure.  And, because they serve more people, they are required to meet stricter regulations

Do you receive and read water quality reports sent out by your water provider? The EPA has a page that describes the Consumer Confidence Reports that are provided by public water companies every year. The Safe Drinking Water Act of 1996 mandated that public water companies were to prepare annual water quality reports and make them available to all customers. NSF also maintains a page that describes how to interpret consumer confidence reports.  Drinking Water Quality Reports also has valuable information as does the Purdue Extension.

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Some information for well owners or people who use surface water for drinking.  People with private water supplies are responsible for the safety of their own drinking water.  While all wells, springs, and surface water should be tested regularly, there are some situations where it is critical to know what is in your water:

	If you use surface water or water from an unconfined aquifer and have any sources of pollution nearby, you are at risk for contaminated water.
	If you or members of your family are at higher risk of health problems from contaminants, you should know what is in your water.
	If the quality of your water suddenly changes - new taste, odor or color.

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Poorly designed or maintained septic systems are a potential source of contamination for wells or springs mostly in unconfined aquifers.  The most common contaminants from septic systems tend to be E. coli and nitrates, but if other chemicals are flushed into the septic system by you or your neighbors, they can become part of the ground or surface water pollutants as well.  another site.

Information about private wells:
EPA - Private Drinking Water Wells 
The Water Research Center
    private well owner booklet
    the Keystone Clean Water Team
 National Environmental Services Center
 California State Water Resources Control Board (pdf)

Water Testing: If you use municipal water you should be able to obtain a water quality report yearly and, except for special circumstances, would probably not need to test your water.  If you use well, spring, or surface water, it is important to test your water periodically  for contaminants liable to be present in your water.  As discussed above, water quality from a water source can change over time - particularly in surface water or shallow, unconfined aquifers.  The University of Tennessee Agricultural Extension Service article, Safety of Private Water Supplies, has important suggestions and information about testing for the safety of your well water.

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Where You Live Can Impact Your Water Quality:

Home Located in an Industrial Area:   The range of possible industrial pollutants is extremely large. Important contaminants include heavy metals and many thousands of kinds of manufactured chemicals.  Water contamination can occur from: Emissions into the atmosphere that either settle onto or wash onto the earth's surface and from there into the surface or ground water. Waste dumps that leak into surface or ground water. Leakage from storage areas of chemical products or their precursors. Accidents and spills during transport of chemicals. Direct dumping of contaminants into surface water for disposal. A recent movie that examines some consequences of industrial pollution is A Civil Action starring John Travolta.

Home Located in an Agricultural Area: Farms can have many potential sources of pollution for the underlying water, including: manure lagoon, feedlot / barn, septic system, earthen silage pit, fuel storage tank, chemical storage area, chemical mixing area, dump or landfill, and fields on which fertilizers or pesticides have been applied.  For more information on farm wells, go to: Well Water Location.   In addition to the health effects of nitrates on children nitrates in drinking water have also been associated with other health problems.

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Chlorinated Water and the Risk of Disinfection Byproducts:

Is your water Chlorinated? Most municipal water treatment plants use chlorine or chloramine to disinfect the water before it leaves the treatment plant and/or keep the water biologically safe during the distribution process.  Many well users also use chlorine to disinfect their water.     Chlorine is a very effective and economical disinfectant, and since cities began the process of chlorination in the early 1900s, countless lives have been saved.  However, chlorine reacts with organic material in the source water to produce a group of chlorinated organic compounds collectively known as Disinfection Byproduct (DBPs) which can themselves slightly increase health risks.  These DBPs include: Total Trihalomethanes (TTHMs) which include chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Haloacetic Acids (HAAs) which include dichloroacetic acid and trichloroacetic acid. According to several EPA articles:  "While disinfectants are effective in controlling many microorganisms, they react with natural organic and inorganic matter in source water and distribution systems to form DBPs.  Results from toxicology studies have shown several DBPs to be carcinogenic in laboratory animals.  Other DBPs have also been shown to cause adverse reproductive or developmental effects in laboratory animals.  Several epidemiology studies have suggested a weak association between certain cancers (e.g., bladder) or reproductive and developmental effects, and exposure to chlorinated surface water.  More than 200 million people consume water that has been disinfected.  Because of the large population exposed, health risks associated with DBPs, even if small, need to be taken seriously."   Chloramine use produces fewer regulated disinfection byproducts than chlorine disinfection, but that may just be because chlorine has been in use far longer and has been studied extensively, and the chloramine byproducts have not been studied as long.   In 1979, the EPA set an interim Maximum Contaminant Level (MCL) for TTHMs of 0.10 mg/l (or 100 microgram/l) as an annual average.  This applies to any community water system serving at least 10,000 people that adds a disinfectant to the drinking water during any part of the treatment process.  By 2002 the MCL for TTHMS will be lowered to 0.08mg/l (or  80 ug/l) and a MCL for HAAs will be set at 0.06mg/l   There is epidemiological evidence suggesting a weak association between the consumption of chlorinated drinking water and the occurrence of bladder, colon, and rectal cancer (and possibly even some brain cancers).   In epidemiological studies, investigators compare health effects in a population of people who drink water containing higher levels of DBS with a similar group of people who drink water with lower levels of DPS.  Estimates in the role of DBPs and cancer have changed over the years because it is extremely difficult to determine exposure levels to DBPs over decades and determine what the contribution of that exposure might have been to the development of some cancer.  This article provides some history of the process.  It is a tough balancing act between adding too little chlorine (resulting in more microbial contaminants and fewer DBPs), and too much chlorine (resulting in dead microbes and higher levels of DBPs).  The World Health Organizationn concluded, the risk of death from pathogens is at least 100 to 1000 times greater than risk of cancer from disinfected by-products and risk of illness from pathogens at least 10,000 to 1 million times greater.  More information about how to understand epidemiological studies.   A 1996 study by King and Marrett concluded "that the risk of bladder cancer increases with both duration and concentration of exposure to chlorination by-products".  They found that those exposed to chlorinated surface water for 35 or more years had a 1.4 times increased risk of bladder cancer compared with those exposed for less than 10 years, and those exposed to an estimated THM level greater than 49 micrograms/liter for 35 or more years had 1.63 times the risk of those exposed for less than 10 years.

Populations At Greater Risk from Water Contaminants:
        Pregnant Women, Children, Elderly, Immunocompromised

Any person who requires water of a specific microbiological purity should follow the advice of their doctor or local health officials regarding the use and consumption of tap water treated by ANY purification system.

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Risk of Lead Contamination:

"Lead in drinking water rarely contributes large amounts of lead exposure to people," said Joel Schwartz, professor of environmental health at the Harvard School of Public Health.  But he said lead in drinking water probably contributes to a child's total lead exposure, because in New England, ''we tend to have corrosive water and old pipes." Beth Daley, Boston Globe interview | November 17, 2005

A 2005 article, Reducing Lead Exposure from Drinking Water: Recent History and Current Status, by Richard P. Maas, et. al. concluded: Nationally, lead exposure from drinking water has been recognized as a substantial (14% to 20% of total) contributor to overall childhood lead exposure in the U.S.  Although no reliable national statistical trend data have been published to date, average tap water levels in the U.S. as a whole have almost certainly decreased since the mid-1980s, as in New York City, through the banning of lead solder, the introduction of corrosion-reduction measures by public water systems, and the discontinuation of leaded-brass faucet fixtures.  However, during the same period, medical and epidemiological studies have determined that even very low level lead exposures cause substantial and permanent IQ and learning deficits in young children, and that low-level but widespread lead exposures, such as from drinking water, may have disproportionately large health effects.  Thus, lead in drinking water should still be considered an important public health issue to be addressed.

Most well or city water does not naturally contain lead. Water usually picks up lead inside your home from household plumbing that is made with lead containing materials.  Lead has traditionally been used as an alloying material in brass and bronze to prevent porosity and enhance machinability. The good news is that, under the Reduction of Lead in Drinking Water Act, signed Jan. 4, 2011, �lead free� will be redefined as �not more than a weighted average of 0.25% lead when used with respect to the wetted surfaces of pipes, pipe fittings, plumbing fittings, and fixtures.�  Wetted parts include any product used to convey water anticipated for human consumption. The bad news is that the new rules do not require replacing old plumbing and fixtures that may contain some lead. Even homes that have lead pipes may not normally have lead in the tap water because a layer of scale has built up and protects the pipes from corrosion.  Any change in the water quality or if the pipes are disturbed. Lead-contaminated drinking water is most often a problem in houses that are either very old where the amount of lead used was greater, or fairly new where some lead was still allowed but protective scale has not yet formed. Plumbing installed before 1930 is most likely to contain lead. Lead solder was banned in the US in 1986, but the ban has not been universally adhered to. Pipes and brass faucets and fittings installed between 1986 and 2014 can also leach lead, even though they are labeled "lead-free".  The term �lead free� meant that solders and flux could not contain more than 0.2 percent lead, and that pipes, pipe fittings and brass or bronze fixtures could not contain more than 8.0 percent lead. Soft water and water of low pH is more liable to dissolve any lead that might be in the pluming and prevents the formation of a protective scale. Check for lead water pipes - particularly if your home was built before lead was banned from pipes. Inside your home - Locate the pipe leading to the kitchen tap, and follow it as far as possible until it exits your home. Unpainted lead pipes are dull gray and soft.� If you scrape the surface gently with a knife, you will see the shiny, silver-colored metal beneath. If possible, check the supply line from the water main to your home - Try to find a place where the supply line is accessible (water meter for example) and check for indications of lead pipe. Other types of pipe in use Copper - bright copper-brown color may have silver colored metal around the soldered joints - the solder may contain lead. Iron/Steel - black, may be rusty, and is quite hard.  The pipe may have a shinny galvanized coating. Plastic - may be white, blue, gray, black, etc. Lead compounds may also be present in some plastic plumbing components. Lead may be used in the manufacture of the plastic plumbing products as a plasticizer. Plastic plumbing components that are certified by the NSF International do not contain lead. Plastic materials certified by NSF are recommended for potable water plumbing applications.

Since lead may enter your drinking water from the pipes in your home or apartment  building, the only way to know if there is lead in your drinking water is to have it tested at your tap.  The EPA�s regulation for lead in drinking water allows up to  15 parts per billion of lead in up to 10 percent of all houses that water providers sample.  If test results show more than 15 ppb of lead in over 10 percent of samples, then water  providers must notify ALL residents supplied by their water and develop a plan for reducing lead levels.  As demonstrated in the article below about Denver Water (which I drink - after filtration), water conditions can change over time - even in a large municipal water system.

A November 2012 article in the Denver Post reported that, "While sources of Denver water in the mountains traditionally have been safe, more than half of [Denver] homes may have lead pipes � either inside the houses or connecting them to Denver Water mains.  ...Drinking water in one out of eight Denver homes with lead plumbing may be contaminated with lead.  ...The 13 percent of Denver homes that had high lead levels, up from 8 percent of homes in 2011, is the highest percentage logged in 12 years, according to Denver Water data provided to the Denver Post.  ...The lead concentrations measured in samples from 60 homes [built between 1880 and 1989 that still have lead plumbing] exceeded the federal drinking water standard of 15 parts per billion by as much as 3.8 times."  All 1.3 million metro residents served by Denver Water were notified and advised of precautions they could take to reduce possible exposure.  According to the census bureau, there were about 266,000 households in Denver between 2009 and 2013, so families in as many as 17,200 homes (13% of 133,000) could have experienced elevated lead levels in 2012 - reported in the 2013 Denver water quality report.  2014 update:  Although Denver Water was compliant with regulations, eight of the 117 homes tested (6.8% and as many as 9,000) may have had lead levels above 15 ppb in their drinking water.

You have the greatest health risk from lead exposure, even with short term exposure, if: you are a young child - check out (Protect Your Children From Lead Poisoning) you are pregnant - Environmental policies and public health education programs have led to significant reductions in cases of lead exposure in the United States. Despite these improvements, approximately 1% of women of childbearing age (15�49 years) have blood lead levels greater than or equal to 5 micrograms/dL (2012 Committee on Obstetric Practice). During pregnancy, hormone changes can cause lead stored for years in a woman's bones to be released into the blood.  This lead probably won't affect the mother, but could pose risks for an unborn baby - Understanding lead poisoning.  An extremely detailed paper on lead and pregnancy from the CDC.

An adequate calcium intake can help protect against lead poisoning.  It has been observed in animals and humans that both the absorption and retention of lead decreases as calcium intake increases.  Many children at risk for exposure to excess lead are also those who live at the poverty level, and may consume a diet with insufficient calcium.  Therefore, increasing consumption of low-cost, calcium rich foods can reduce the severity of the effects of lead exposure.  The RDA for calcium for children ages 1 to 10 is 800 mg per day.  Nutrition and Childhood Lead Poisoning.  From another source, dietary calcium may also help prevent the transfer of lead from a pregnant women to her developing fetus.

If your home is at risk for having lead in pipes or fixtures and your drinking water has not been tested for lead (particularly if you notice blue/green staining), or if your water does contain lead, seriously consider taking the following precautions. The staining is copper, which is not nearly as harmful as lead, but if copper is dissolving from pipes and fixtures, it is possible that any lead that is present would be dissolving into the water as well. Install one of the several treatment methods that are effective at removing lead: activated carbon filtration (make certain filters are NSF certified to remove lead), reverse osmosis, or distillation.    If you remove the lead from your drinking water, you do not have to worry about the other precautions below.  There are water treatments that remove only lead, however.  if you make the decision to remove lead you might want to look at a more comprehensive treatment solution that would protect against a wider range of contaminants as well as lead. If the water has not been used in a particular faucet for six hours or longer, run the cold water tap until the water is noticeably colder, about a minute, to "flush" the pipes.  The longer water has been sitting in your home's pipes, the more lead and other dissolved metals the water may contain.  Buildings built prior to about 1930 may have service connectors made of lead. Letting the water run for an extra 15 seconds after it cools should also flush this service connector.  You may wish to fill water bottles and store them the refrigerator for later use after flushing the water lines.   Flushing may not be effective in a high-rise building. Use only cold water for drinking, cooking, and especially making baby formula. Hot water dissolves materials better than cold water and thus may contain higher levels of lead. Frequently clean the screens and aerators in faucets to remove captured lead particles. If building or remodeling, only use "lead free" piping and materials for plumbing.  Still, as noted above, even "lead free" brass fixtures probably have traces of lead in them. If you are served by a public water system contact your supplier and ask whether or not the supply system contains lead piping, and whether your water is corrosive. If either answer is yes, ask what steps the supplier is taking to deal with the problem of lead contamination.

Lead exposure from drinking water is not a hypothetical issue:

Within one week's time I received these two questions concerning lead contamination.�� Even though I run this site and should know better, I am sometimes lulled into a false sense of� security that everything's OK "out there" - that people know about the dangers of lead, and� everyone has taken precautions to minimize exposure - both in their homes and in their drinking water. These questions,�however, prompted me to place even more emphasis on lead education for those at risk.�

If you are are just browsing water issues, and are not in the high risk category for lead poisoning (pregnant or have a young child), but you know someone who is pregnant or has young children, please have them read these examples of how families were caught unaware of the potential risks of lead in their drinking water.

Question 1: We have recently found out that we have a lead pipe coming into our house from the main line in the street. We live in B___, Ohio. It comes into our house through the basement wall only about 2-4 inches and is behind the water softener so it is not very visible. We just had our water tested for the first time and it back at a whopping 147!!!! We are currently waiting on blood tests to come back on my 2 1/2 year old son. He does have speech delay, anti-social behavior and attends a special school for these and other learning and behavior problems.  I have many questions regarding this whole situation. 1. Why doesn't the city have to notify the homeowners that they have this lead pipe going into their houses? I realize that past the main line is my responsibility but they are more aware of this than I am since I do not work with the equipment that is underneath my yard. They just put a new water meter at my house two months ago because mine broke. The lead pipe is connected to the meter. If they didn't know it before, they should at least know it now.  2. Why is lead pipe still allowed to be used? I know that you can no longer install it but what about what is already there? Why aren't there laws in place to these pipes replaced?  3. When we bought the house 4 years ago, there was a disclaimer from the previous owner's verifying that there was no lead based paint in the house. Why aren't those same statements required about lead pipe?  How do you think I feel as a mother knowing that I drank this water while I was pregnant for my son, and then mixed his formula with this water, and now hand it to him every day in a glass, sometimes 4-5 times a day, and that I basically gave him his current speech and learning condition?? Why aren't there laws in place to prevent these types of things from happening? If you could direct me in the right direction for some of these answers, I would be MOST grateful!!! Also, thank you for letting a VERY upset and discouraged mother vent!! B____ Question 2: I have just discovered that the pipes in my bathroom are made from lead. I am 5 months pregnant and have used this water to drink in the evenings (1 or 2 glasses a day). What potential damage could have been done to the unborn baby?  Many thanks in advance. A____

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Contaminants and Sensory Clues:

Great looking, smelling, and tasting water is no guarantee that you have safe water!   A number of water contaminants can be identified by characteristic smell, taste, color, or staining properties if they are present in high enough quantities.   Click here for tables that will help you identify the possible presence of some water contaminants without testing. It is important to understand, though, that the identification of some contaminants using the tables in the link above is only one way to begin the process of understanding your water quality - it is definitely NOT intended to provide a list of all harmful contaminants that might be in your drinking water.  Many contaminants, lead, mercury, E. coli, disinfection byproducts - in fact the majority of the harmful contaminants that might be in your drinking water have no color, taste or smell - nor would they be visible - at harmful quantities.  If you suspect the presence of harmful contaminants in your water, testing is critical to planning an effective treatment solution.  Since municipal water is regulated and monitored in developed countries, this advise is mostly applicable to those who depend on water from private, unregulated sources.

If your water normally looks, tastes, and smells good and then suddenly becomes cloudy (turbid) or acquires a bad smell or taste it may be an indicator that the treatment process has failed and your water is chemically or biologically unsafe.  Unless you have a distillation or high quality RO system, immediately start using bottled water, or otherwise purified water until you have determined that your water is safe.  That would also be a very good time to consider investigating a permanent water treatment solution.

Water Distribution | The Water Cycle | Aquifers

The geographic region where people live is an important contributing factor to both the quality and availability of fresh water.  This map shows the percentage of population with access to safe water by country.  Another interesting article from The Why Files takes a look at water availability in different regions of the world.  Every one who is able to turn on a faucet and expect to fill their glass with clean, safe water should read this report - although 92% of the world's global population is expected to be using improved water sources by 2015,  that still leaves around 600 million children and adults without access to safe water.

Where does your water come from: According information on the US Geological Survey (USGS) web site, the earth contains 332,500,000 cubic miles of water, and over 70% of the earth's surface is covered by water.  Although water is abundant on the earth, most of it is unusable for drinking, agriculture, or industry.    Fresh, water accounts for only about 2.5% of the world's total water supply, the rest is salt water.   The majority of the fresh water (68.6%) is locked away as ice in the polar ice caps, continental ice sheets and glaciers. There are only two natural and easily accessible sources of fresh water for all individuals in the world, whether they live in the most remote area of the earth or in the middle of New York or Beijing:  Surface water and Ground Water.   Surface water, such as rivers and lakes, only accounts for about 1.3% (108K cubic miles) of the worlds fresh water reserves.  Water in the air, in plants and animals etc., accounts for such as tiny percentage that it has been included in the surface water category. The rest of the world's fresh water supply, about 30.1% is groundwater which can be difficult and expensive to extract - and difficult to replace once used. As the diagram below shows, only about 0.03% of the water on earth (roughly 103,000 cubic miles) is fresh and on the surface, available for drinking, agriculture, or industry.  About 99.97% of the water on earth is either salty (mostly in the oceans), locked up as ice (mostly in the polar ice caps), or locked up as ground water which is difficult and expensive to extract.   Note: The values below can be different from different sources, but the bottom line is that a very small fraction of the total water on our planet is available for drinking without significant investments in obtaining and/or treating it.  A more detailed breakdown of water availability on earth can be found on the USGS website.

An interesting demonstration of water availability on the earth: Fill a gallon jar with water which represents the total volume of water on the earth Pour the relative amounts into glasses, measuring cups, or beakers to actually show how the water is proportioned. This is an easy demonstration to show the amount of water in the different categories, particularly that small fraction which is available for human use.

1 gallon = 4 quarts = 128 fluid ounces (fl oz) = 757 tsp Based on the figures above, if all the earth's water equaled One Gallon: 97.5% = salt water = 3.9 quarts = 124.8 fl oz   2.5% = fresh water = 3.2 fl oz = 18.9 tsp      68.6% of the 2.5% is in glaciers and ice caps = 2.2 fl oz = 13 tsp      30.1% of the 2.5% is in ground water = 1 fl oz = 5.7 tsp        1.3% of the 2.5% is in rivers and lakes = 0.04 fl oz = 0.25 tsp

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The Water Cycle: Fortunately, Earth's water supply is not static - we don't just use up all the fresh water and then run out.  The fresh water supply is constantly naturally purified and replenished (although human activity can negatively impact this process).  The overall water distribution on earth is in balance: Evaporating from lakes, streams, rivers, oceans, land surfaces, plants, animals, and ice fields  Circulating in the atmosphere as water vapor Condensing of the water vapor onto small suspended particles of salt, dust, ions, etc. to form clouds and fog Precipitation as rain, snow, hail, etc. when condensed water droplets become too large or they freeze and become too heavy to remain in the air and fall to the ground Once on the ground the water can: Flow along the surface in streams and rivers or through the ground back to the oceans Remain in fresh water lakes Enter plants and animals Flow through the soil to recharge groundwater aquifers Flow out of groundwater aquifers into rivers and lakes This is the Physical Water Cycle or Hydrological Cycle that nearly everyone has studied in school at one time or another. When water evaporates it leaves most of the contaminants behind - this is the process behind distillation.   The relatively pure water vapor can then pick up vaporous or particulate pollutants from the atmosphere as it precipitates. After falling on the Earth's surface as rain, snow or ice, the water can dissolve more pollutants from the soil or rocks it contacts. Pollutants can also be directly added to water during contaminant spills or discharge from factories, agricultural operations, etc. Soil and rock can do a good job of filtering some pollutants out of the water as it percolates through them and into the aquifers.  That is one reason ground water tends to be less contaminated than surface water. There is also a Biological Water Cycle in which water is broken down and reformed in a two step process: Photosynthesis - plants use light energy to break water down into oxygen gas and hydrogen which is used to form carbohydrates (CO2 + H2O + light energy → carbohydrates + O2).  The energy from light is stored as chemical energy in the carbohydrates (sugars).  Carbon dioxide is removed from the environment and oxygen is released. Respiration - plants and animals 'burn' carbohydrates in their cells and use the stored energy to power most chemical reactions of life (carbohydrates + O2 → CO2 + H2O + chemical energy).  Oxygen is removed from the environment and carbon dioxide and water are released.

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Confined and Unconfined Aquifers with Pollution Sources.

The depth of a well is not usually as important as the type of aquifer from which the well draws.  In general, well water from an unconfined aquifer is much more prone to contamination than water from a confined aquifer.  For the teachers who are visiting:  I discovered what appears to be a very interesting  groundwater model that demonstrates confined and unconfined aquifers, how water and contaminants move through aquifers, various soil structures, and watersheds.


A spring forms when the ground level drops to intercept either a confined or an unconfined aquifer (or water pressure in a confined aquifer forces water out through cracks in the confining layer), consequently, they are subject to the same contaminant risks as wells drilled into the aquifers themselves.

Surface water: Even though fresh surface water (in rivers, streams, lakes, and reservoirs) makes up just over 1 percent of the fresh water in the world, about 75 percent of all the water we use in everyday life come from surface water sources.  The other 25  percent comes from ground water.  It is only natural that we heavily use our surface water resources.  It is a lot easier and cheaper to get water out of a river, lake, or reservoir than it is to drill a well and pump water out of the ground.  Also, rivers are more accessible to us -- we generally build our towns and cities next to a river or lake.  Unfortunately, however, the accessibility of surface water makes them very easy to pollute.  Until fairly recently the obvious solution to removing noxious wastes from a person's immediate environment was to dump it into the nearest river and watch it drift out of the "neighborhood". Ground water: Ground water is the largest available reservoir of fresh water. comprising about 12 percent of the available fresh water.  Despite the abundance of ground water relative to surface water, only about 25 percent of the fresh water used in everyday life comes from ground water aquifers.  This is largely due to to the difficulty and expense of using this water source relative to surface water. Groundwater is defined as the water filling spaces between rock particles in special porous rock layers known as 'aquifers'. Perhaps the best way of imaging an aquifer is as a solid sponge. Rainwater trickling down from the ground surface (infiltration) fills the spaces in the rock.  When the water is stopped by an impermeable layer of rock underneath the aquifer (a confining layer) the aquifer begins to fill. Water in an aquifer does not sit still.  It flows through the spaces and cracks in the rock, pulled by gravity and pushed by the force of the water above and behind it.  The water moves from an area where water enters the aquifer (a recharge zone) to an area where water exits the aquifer (a discharge zone).  This movement has the effect of removing a lot of impurities from the water, filtering it through the rock so that groundwater is generally much cleaner than surface water.  As groundwater can be very clean, it may require little or no treatment before being used.  The level of treatment depends on what it is to be used for.  This often makes groundwater a relatively inexpensive source of 'raw water' for public supply.

Unconfined Aquifer: An unconfined aquifer is recharged from surface water directly overlying it.  It is apparent from the diagram above that, in general, an unconfined aquifer is much more prone to contamination than is a confined aquifer. This recharge area is frequently of a greater area and has more development on it than the recharge area for a confined aquifer.   Although filtration takes place as the surface water percolates down through the pores of the soil and permeable rock, if pollutants are present in the recharge area, they will frequently make their way into the aquifer.  Good graphics showing sources of ground water pollution can be found here and here. Water tends to move more rapidly through unconfined aquifers than confined aquifers. Unconfined aquifers are more prone to changes in water quality over time than are confined aquifers, because of the characteristics above.  You can expect seasonal changes and changes after unusual precipitation amounts.

Confined Aquifer: The Recharge area of a confined aquifer may be many miles from the developed areas where wells are drilled into it. The water is filtered as it moves through the rock pores as it is in unconfined aquifers. Often a relatively small area of permeable rock in the recharge area is exposed.  If the recharge area is less developed than the area where the water is used, the water in the confined aquifer will be more pure than the overlying unconfined aquifer or the surface water.   On the other hand, water tends to move through confined aquifers more slowly than in unconfined aquifers.  For that reason, and because they have at least one layer of impermeable rock above them, if contaminants do enter a confined aquifer, it is much more difficult to remove them.

Water in the United States: The USGS Water Science for Schools site has a very interesting graphic showing the Source and use of water in 2005.  At first glance it looks a bit messy and hard to understand, but with some study, it is a very complete picture of where water came from and how it was used.

An excellent site that covers many aspects of Earth's water is hosted by the USGS.  The U.S. Geological Survey's (USGS) Water Science for Schools web site offers information on many aspects of water, along with pictures, data, maps, and an interactive center where you can give opinions and test your water knowledge.  Although it is targeted at school-age children, the information is very complete and presented in a way that can be enjoyed by anyone.

The USGS maintains an on-line Ground Water Atlas of the United States with maps and descriptions of the important aquifers of the Nation.  A description of an extensive aquifer in Texas (the Edwards Aquifer) can be found by clicking here.

The USGS is an excellent resource for learning about watersheds, streams, rivers, lakes, and aquifers in the United States.  The Water Resources Division of the USGS has the principal responsibility within the Federal Government to provide the hydrologic information and understanding needed by others to achieve the best use and management of the Nation's water resources. To accomplish this mission, the Water Resources Division, in cooperation with State, local, and other Federal agencies, Systematically collects and analyzes data to evaluate the quantity, quality, and use of the Nation's water resources and provides results of these investigations to the public. Conducts water-resources appraisals describing the occurrence, availability, and physical, chemical, and biological characteristics of surface and ground water. Conducts basic and problem-oriented hydrologic and related research that aids in alleviating water resources problems and provides an understanding of hydrologic systems sufficient to predict their response to natural or human-caused stress. Coordinates the activities of Federal agencies in the acquisition of water resources data for streams, lakes, reservoirs, estuaries, and ground water. Provides scientific and technical assistance in hydrologic fields to other Federal, State, and local agencies, to licensees of the Federal Energy Regulatory Commission, and to international agencies on behalf of the Department of State. Administers the State Water Resources Research Institutes Program and the National Water Resources Research Grants Program.