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 [Photo: USGS scientists collect water-quality samples.]

USGS personnel collect a water-quality sample on the Missouri River. USGS/Photo by Kelly Brady.


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Water Quality Data

National Water Information System (NWIS)

NWIS provides current and historical water-quality data.

Today's Water Conditions

Water-Quality Watch provides continuous real-time water-quality measurements.
[Sample Water-Quality Watch Map]

Water-Quality Web Services

Web services automate the sharing of USGS and USEPA water-quality monitoring data.

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Additional water-quality data resources are available.

USGS in Your Area

USGS Water Science Centers are located in each state.

 [Map: There is a USGS Water Science Center office in each State.] Washington Oregon California Idaho Nevada Montana Wyoming Utah Colorado Arizona New Mexico North Dakota South Dakota Nebraska Kansas Oklahoma Texas Minnesota Iowa Missouri Arkansas Louisiana Wisconsin Illinois Mississippi Michigan Indiana Ohio Kentucky Tennessee Alabama Pennsylvania West Virginia Georgia Florida Caribbean Alaska Hawaii and Pacific Islands New York Vermont New Hampshire Maine Massachusetts South Carolina North Carolina Rhode Island Virginia Connecticut New Jersey Maryland-Delaware-D.C.

Frequently Asked Questions

  1. How does runoff from large animal feeding operations affect water quality?
  2. How does bioremediation clean up gasoline and oil spills?
  3. Where can I find information about bottled water?
  4. What can be causing our water to have a reddish color?
  5. Can you give me some advice on commercial products such as water filters?
  6. Where can I get information about drinking water contaminants and standards?
  7. What if my drinking water contains E. coli?
  8. What are the federal health limits for water used for drinking water, as well as for swimming and boating?
  9. Where can I find fish consumption advisories for my state?
  10. What are the usual causes of fish kills?
  11. Where can I find a glossary of water terms?
  12. Do you have information about water hardness in the United States?
  13. Where can I find information about the health effects of contaminants in drinking water?
  14. What is a good home treatment for purifying drinking water in case of an emergency?
  15. Where can I find information about the quality of the water in a lake or river near me?
  16. Where can I find information about my local drinking water supply?
  17. Where can I find information about mercury contamination in water?
  18. How does the gasoline additive MTBE contaminate our water and cause health problems?
  19. Why are high nitrate or nitrogen concentrations in water a problem, and what can be done to maintain safe levels?
  20. What can cause our water to have an earthy odor or to smell like rotten eggs?
  21. How does the use of pesticides affect our Nation's water quality?
  22. Where does pure, natural water come from?
  23. How is water naturally filtered or purified?
  24. Where can I find information on water purification techniques?
  25. Can you define safe water?
  26. Where can I find detailed sampling methods for surface water and ground water?
  27. If the sulfur content in my well water is a little high, is it still safe to drink?
  28. Who do I contact to have my well water tested?
  29. What are the permissible levels of trace elements (such as arsenic, copper, iron, lead, and zinc) in water for the water to still be considered safe for exposure/bioaccumulation by people and aquatic life?

1.Q: How does runoff from large animal feeding operations affect water quality?

A: Animal Feeding Operations: Effects on Hydrologic Resources and the Environment highlights many potential effects of animal feeding operations (AFOs) that were discussed at a meeting co-sponsored by the USGS Office of Water Quality and the Toxic Substances Hydrology Program.

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2.Q: How does bioremediation clean up gasoline and oil spills?

A: Bioremediation is the process by which microbes (generally bacteria) or plants transform a harmful water contaminant into a non-harmful substance, much as we turn sugar into carbon dioxide and water. Bioremediation can help clean up ground water contaminated with gasoline, solvents, and other contaminants. Often, the bacteria are already present in the soil or aquifer, and bioremediation takes place naturally. In some cases, the rate of bioremediation is too slow to effectively clean up a plume of contaminated water before it gets to a spring, well, lake, or stream. In those cases, the rate of bioremediation can sometimes be enhanced by adding a substance that acts like a fertilizer to make the bacteria grow and feed more rapidly. This substance, which depends on the local chemistry and hydrology, might be nitrate, or oxygen, or iron, or something else. Additional information is on a bioremediation fact sheet.

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3.Q: Where can I find information about bottled water?

A: The U.S. Food and Drug Administration and States regulate bottled water. For general information about bottled water, some sources are the International Bottled Water Association and NSF International.

The The U.S. Environmental Protection Agency (EPA) provides the following information on bottled water and tap water:

Bottled water is not necessarily safer than your tap water. EPA sets standards for tap water provided by public water systems; the Food and Drug Administration sets bottled water standards based on EPA's tap water standards. Bottled water and tap water are both safe to drink if they meet these standards, although people with severely compromised immune systems and children may have special needs. Some bottled water is treated more than tap water, while some is treated less or not treated at all. Bottled water costs much more than tap water on a per gallon basis. Bottled water is valuable in emergency situations (such as floods and earthquakes), and high quality bottled water may be a desirable option for people with weakened immune systems. Consumers who choose to purchase bottled water should carefully read its label to understand what they are buying, whether it is a better taste, or a certain method of treatment. For more information, download the U.S. Environmental Protection Agency booklet: Bottled Water Basics PDF (2MB PDF). (Source:

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4.Q: What can be causing our water to have a reddish color?

A: Your water might be affected by iron, a commonly occurring constituent of drinking water. Iron tends to add a rusty, reddish brown (or sometimes yellow) color to water, and leaves particles of the same color. If the color is more like black, it could be a combination of iron and manganese. Both of these metals can cause staining of plumbing fixtures or laundry, but they are not known to cause health problems.

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5.Q: Can you give me some advice on commercial products such as water filters?

A: As a government agency, the USGS does not comment on commercial products, but many organizations evaluate consumer products and post product reports on the Internet. NSF International (which EPA and others established for the purpose of certifying water treatment products, among other things), the Water Quality Association (the trade association of treatment companies), the U.S. Consumer Product Safety Commission, or your local health department may also provide information.

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6.Q: Where can I get information about drinking water contaminants and standards?

A: The U.S. Environmental Protection Agency has contaminant-specific fact sheets for many drinking water contaminants on their Web page Drinking water and health: What you need to know. Click on "What are the health effects of contaminants in drinking water?" This page also addresses the standards for levels of contaminants in drinking water under the heading Drinking Water Standards Program. These drinking water standards were developed by EPA after considering information on the occurrence and distribution of the contaminant, the health effects of the contaminant at various concentrations, and the economic costs for treatment to remove the contaminant. More information can be obtained from the EPA Office of Ground Water and Drinking Water.

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7.Q: What if my drinking water contains E. coli?

A: "E. coli is a type of fecal coliform bacteria commonly found in the intestines of animals and humans. E. coli is short for Escherichia coli. The presence of E. coli in water is a strong indication of recent sewage or animal waste contamination. Sewage may contain many types of disease-causing organisms." The full fact sheet is on the web at:

The fact sheet begins with a discussion of one rare strain of E. coli, strain 0157:H7, that has caused serious disease. Fortunately this strain is rarely encountered. The great majority of E. coli strains do not themselves cause disease. However, since E. coli typically grows in the gut of humans, warm-blooded mammals, and birds, and is normally excreted by the billions in their waste, and it normally dies or is eaten by other microbes within a few days or weeks of being released into the environment, then finding E. coli in your drinking water is a good indication that sewage or animal waste was recently in contact with your water. And since sewage and animal waste can carry a wide variety of other microbes, some of which do cause disease, the presence of E. coli suggests that other, more dangerous, microbes might be present.

Public water supplies are usually disinfected with chlorine, ozone, or some other process. Finding E. coli in a public water supply indicates that the disinfection process was not working, or that contact with the waste occurred after the water was treated. If your sample was from a public water supply, you should notify the water supplier. If your sample was from a private well or other source, you should take some actions to protect that source. Suggestions can be found in:
USDA Farm*A*Syst/Home*A*Syst:

If you suspect the water source, whether public or private, may still be contaminated, you should consider drinking bottled water, or boiling your drinking water, or treating it with iodine, bleach, or disinfection tablets as described in EPA's fact sheet on emergency disinfection of drinking water.

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8.Q: What are the federal health limits for water used for drinking water, as well as for swimming and boating?

A: The U.S. Environmental Protection Agency sets standards for water that could affect human health and works with local government officials to reduce health risks in water where you swim or play. You may want to contact your local health deparment or state drinking water office for information specific to your area. Some EPA Web sites you may wish to check are:

Another source is the USGS Acute Toxicity Database.

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9.Q: Where can I find fish consumption advisories for my state?

A: Most states have set fish (and wildlife) consumption advisories and recommended consumption levels. The state agency responsible for these limits varies. Check the state government section of your local telephone directory for listings such as the Department of Health, Department of Natural Resources, or Division of Environmental Protection. Examples of consumption advisory information can be found at Fish Advisories.

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10.Q: What are the usual causes of fish kills?

A: Many, but not all, fish kills in the summer result from low concentrations of dissolved oxygen in the water. Fish, like all other complex life forms, need oxygen to survive. They get theirs in the form of oxygen gas dissolved in the water. That's why it's important to have an aeration device, a bubbler, in your home aquarium. Warm water holds less dissolved oxygen than cold water, so summer is the time when fish can have a hard time getting enough oxygen. Other organisms use oxygen, too, including the algae that grow in the summer and bacteria that degrade organic matter. During the day, the algae produce oxygen through photosynthesis, but at night, when photosynthesis stops, they and other organisms keep respiring, using up oxygen. So on warm summer nights during algal blooms, the dissolved-oxygen concentration sometimes drops too low for the fish, and a die-off can occur. This can occur as a result of purely natural conditions or because of human activity that results in adding nutrients, nitrogen and phosphorus, to water systems. Nutrients come from many sources, fertilizers, automobiles, sewage, manure, and others. An excess of nutrients tends to speed up the growth of algae and diminish the availability of dissolved oxygen, especially in hot weather, sometimes resulting in fish kills. Low dissolved oxygen can result from other factors, too, such as poor flushing or circulation, dredging, or a sudden rain after a dry spell.

Fish kills also can occur as a result to toxic compounds released into a body of water. In order for this to occur, the toxic compound must be fairly highly concentrated. In a large water body (such as the Chesapeake Bay) this would require a very large amount of the toxic compound, and a release site fairly close to the affected fish.

Another cause of fish kills, which has had a lot of publicity in the last few years, is infections caused by fish pathogens such as the dinoflagellate, pfiesteria. If you would like more information about this topic, one source of information is the Web page USGS Chesapeake Bay Activities.

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11.Q: Where can I find a glossary of water terms?

A:The USGS Water Science for Schools Web site has a link to "Water Science Glossary of Terms". This page offers links to additional glossaries. The U.S. Environmental Protection Agency also has a Drinking Water Glossary.

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12.Q: Do you have information about water hardness in the United States?

A: You can view a national map of hardness in surface water. Hardness data (reflecting mostly calcium, plus a little magnesium) for individual drinking-water suppliers is on the following pages:

It is important to note that the U.S. Environmental Protection Agency has not set a legal limit or standard for hardness in water. This is primarily because the constituents that contribute to hardness (generally calcium and magnesium ions) are not toxic; that is, they do not cause harmful health effects. Instead, there is a generally accepted division of water into categories of soft, moderately hard, hard, and very hard, as explained in the water hardness chart. Most water utilities try to provide water that is not in the very hard category because of the unpleasant effects such as scaling in equipment and the need for more soap and synthetic detergents. In addition, many homeowners in hard-water areas use water softeners to further reduce hardness by substituting sodium for calcium and magnesium.

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13.Q: Where can I find information about the health effects of contaminants in drinking water?

A: The EPA Office of Ground Water and Drinking Water Web page Drinking water and health: What you need to know has a link to "What are the health effects of contaminants in drinking water?" This link connects you to fact sheets for many contaminants.

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14.Q: What is a good home treatment for purifying drinking water in case of an emergency?

A: The Federal Emergency Management Agency (FEMA) lists several ways to purify water for human consumption on their Preparedness Web page. Also, the EPA fact sheet Emergency disinfection of drinking water is available in English and Spanish.

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15.Q: Where can I find information about the quality of the water in a lake or river near me?

A: The USGS Web site Water Resources of the United States can direct you to information about your local water body. Under the heading "Local Information" click on "Local Websites & USGS Contacts in Your State!" There you can select your state on a map to find local information.

Below "Local Information" on this site is a link to "Connections." If you click on the link "Search USGS Websites" and type a name (such as "Mississippi") in the Search field and then click "seek", a list of search results is shown.

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16.Q: Where can I find information about my local drinking water supply?

A: The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports often are sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants are in it, and at what levels.

The U.S. Environmental Protection Agency offers information about local drinking water systems through their Local Drinking Water Information Web page. Many water suppliers are now posting their water-quality monitoring results on the Web, and these results can be accessed from this site.

Another source of information is the EPA site Surf Your Watershed. This site answers questions such as, "Where does my drinking water come from?"

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17.Q: Where can I find information about mercury contamination in water?

A: Information is available through the USGS Mercury Studies Program.

18.Q: How does the gasoline additive MTBE contaminate our water and cause health problems?

A: Suggestions for reading about methyl tert-butly ether (MTBE), one of a group of volatile organic chemicals used as solvents, fuel additives, fuels, and disinfection byproducts, is available at the USGS Web page A National Assessment of Volatile Organic Chemicals in Major Aquifer Systems and Rivers. EPA also has a page on MTBE in drinking water.

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19.Q: Why are high nitrate or nitrogen concentrations in water a problem, and what can be done to maintain safe levels?

A: Nitrate (NO3) is a common inorganic form of nitrogen. Chemically, it is an anion with a single negative charge, consisting of one atom of nitrogen and three atoms of oxygen. Because it is an anion, it is soluble in water. Plants normally use nitrate as their source of the nitrogen needed by all living things, and so nitrate is considered a nutrient for plants. Excessive concentrations of nitrate in lakes and streams greater than about 5 milligrams per liter (measured as nitrogen), depending on the water body, can cause excessive growth of algae and other plants, leading to accelerated eutrophication or "aging" of lakes, and occasional loss of dissolved oxygen. Animals and humans cannot use inorganic forms of nitrogen, so nitrate is not a nutrient for us. If nitrate-nitrogen exceeds 10 milligrams per liter in drinking water, it can cause a condition called methemoglobinemia or "blue baby syndrome" in infants. Some recent studies have indicated a possible connection between elevated nitrate concentrations and cancer.

Nitrate can get into water directly as the result of runoff of fertilizers containing nitrate. Some nitrate enters water from the atmosphere, which carries nitrogen-containing compounds derived from automobiles and other sources. Nitrate can also be formed in water bodies through the oxidation of other, more reduced forms of nitrogen, including nitrite, ammonia, and organic nitrogen compounds such as amino acids. Ammonia and organic nitrogen can enter water through sewage effluent and runoff from land where manure has been applied or stored.

Water-quality regulatory agencies seek to avoid high concentrations of nitrate in water to minimize both of the problems noted above. Nitrate standards take two forms: drinking-water standards, designed to prevent adverse human-health effects, and ambient-water standards, designed to prevent excessive eutrophication in lakes and streams. Drinking-water standards for nitrate have been around since at least 1974, when the Safe Drinking Water Act was passed, and probably well before. States may set their own drinking-water standard for nitrate, but most or all use the EPA standard of 10 milligrams per liter (measured as nitrogen). Ambient-water standards have also been around for years, but each State has decided on what standards to use, if any. The EPA is just now setting guidelines for determination of ambient nitrate standards for different water bodies in different regions. General information of EPA's programs for water-quality standards and criteria is available at:

A good contact at EPA to answer questions about standards is the Office of Ground Water and Drinking Water.

Keeping drinking water free of excessive concentrations of nitrate involves a multiple-barrier approach. The most effective strategy is prevention--keeping chemicals that contain or can generate nitrate out of the water. This means managing agricultural operations to minimize application of fertilizer and to minimize runoff of fertilizer that is applied. Some farmers are now using computerized maps of their fields, calibrated to the specific soil and water conditions in various parts of their fields, to restrict the application of fertilizer to only what is needed for each part of the field. In some countries, for example Switzerland, drinking-water providers enter into contracts with farmers in their source areas in which farmers receive subsidies to eliminate fertilizers and use organic farming methods. Prevention also means proper handling of manure and animal waste lagoons, to minimize the discharge of animal waste or waste runoff to streams. Nitrate contributions from other sources can also be curtailed, for example by adding tertiary treatment, or by nutrient removal, to sewage treatment plants, and by controlling emissions from automobiles.

In addition to prevention, drinking-water providers may use advanced treatment techniques to remove nitrate from water. For example, Des Moines Water Works uses advanced ion-exchange technology to remove excess nitrate and remain below the 10 mg/L standard. In a typical year, this is needed mostly during the spring, following spring runoff after the application of fertilizer.

A good article about the occurrence of methemoglobinemia can be found at:

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20.Q: What can cause our water to have an earthy odor or to smell like rotten eggs?

A: A frequent cause of musty, earthy odors, especially toward the end of the summer, is naturally occurring organic compounds derived from the decay of plant material in lakes and reservoirs. The odors can be objectionable, but generally are not harmful to health. However, odors can be caused by other constituents as well, so you may want to call your local Health Department and mention the odor to them.

In some parts of the country, drinking water can contain the chemical hydrogen sulfide gas, which smells like rotten eggs. This can occur when water comes into contact with organic matter or with some minerals, such as pyrite. The situation mostly occurs as ground water filters through organic material or rocks.

The best way to find out what is in your water is to have the water tested by a state certified laboratory. A list of these labs is available from your State Certification Officer.

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21.Q: How does the use of pesticides affect our Nation's water quality?

A: Information on pesticides and herbicides and on nutrients is available from the USGS National Water-Quality Assessment Program.

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22.Q: Where does pure, natural water come from?

A. This seems like a pretty straightforward question, but there are some interesting issues that come up in making a response.

First, the words "pure" and "natural" don't really mean the same thing. Pure water is a kind of theoretical concept, it means water that has nothing in it except H2O (hydrogen and oxygen). Absolutely pure water doesn't really exist in nature. Water, known as the "universal solvent," always contains traces of the substances with which it has been in contact. These may include gases such as carbon dioxide, nitrogen, and oxygen from the air, minerals such as calcium and silica from rocks, and organic matter such as weak organic acid from soil and vegetation. This is not bad. Most of these naturally occurring substances are harmless and, in some cases, beneficial. Most people think the taste of water is improved by moderately low concentrations of naturally occurring minerals, such as calcium carbonate. In the laboratory, with processes such as distillation, reverse osmosis, and de-ionization, we can remove almost all of these natural impurities from water and make it almost pure. Most people think such water has little taste. And when it comes to oxygen dissolved in water, fish and other organisms that live in water would not be able to live without this "impurity."

So, by "pure, natural" water, you probably mean natural, potable water that contains no contaminants introduced by humans, such as pesticides, pathogenic microbes, nitrates, metals, and other toxic chemicals. Notice the term "potable." Some natural waters contain too much of naturally occurring drinking-water contaminants--salt, arsenic, sulfur, or radon, for example--to be drinkable or good-tasting. Another common natural ground-water contaminant is iron. Iron is not harmful, but at high concentrations it stains laundry and plumbing fixtures. The best way to find uncontaminated natural potable water is to look for parts of the hydrologic cycle where water has been isolated from both these natural contaminants and from human influence. The oceans are out, because of the salt. So is the atmosphere, because moisture in clouds picks up traces of pollutants from the air. This also eliminates rain. Most rivers and most lakes are affected by impurities in rain and in the runoff that comes from the land surface. (It's interesting to note, however, that the water from a huge tropical river such as the Amazon has a fairly high level of purity, since most of the material that can be leached from the soils of its watershed have already been leached out. Likewise, the water in rivers and lakes in fairly pristine areas such as northern Canada is relatively pure.)

Getting back to the question, we're left with ground water and ice. Glacial ice that has been frozen and isolated for thousands of years is a good source of uncontaminated natural water, and some bottling companies take advantage of this fact. With ground water, the level of purity depends on the isolation. Shallow ground water, such as you might draw from a 100-foot deep domestic well, probably has been in the ground less than 50 years, and so might contain human-derived contaminants (not all shallow wells are contaminated, but most have at least trace amounts of some contaminants). The huge volume of ground water stored in deep aquifers, especially in deep aquifers protected by overlying impermeable layers, is a major source of uncontaminated natural water. This water may have been underground for more than 10,000 years. If this water has not been in contact with the naturally occurring contaminants mentioned above, it can be an excellent source of drinking water. Many water bottling companies make use of wells or springs that tap these aquifers. They can be found in many parts of the United States and in many foreign countries.

We have been describing a special case of safe water; that is, natural, potable water that has no trace of human-induced contaminants. Many other types of water can be considered safe for most users. If the concentrations of contaminants are so low that they are well below the levels shown to cause health problems, the water is considered safe, even though it is not pure or totally contaminant-free.

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23Q: How is water naturally filtered or purified?

A: A basic introduction to natural filtering of water can be found on-line at the USGS "Water Science for Schools" website. The address for the site's ground-water-quality page is:

Natural filtering is a big topic. Some filtering takes place when water flows over the ground, such as when muddy water from a plowed field or a construction site flows through grass or weeds on its way to a stream. Some of the mud is filtered out. In addition, some filtering takes place when the water is in lakes or streams, through the actions of plants and bottom-dwelling animals (like freshwater clams and mussels) that take in water, remove nutrients, and put it out again. Here's a page that talks about filtering in wetlands:

Here's another, longer, but very good piece about wetlands. The part about natural filtering is in the section called "maintenance of water quality":

A lot of filtering takes place in the uppermost layer of sediment at the bottom of a lake or stream. This is called the hyporheic zone, and it's full of bacteria and other microorganisms that bring about chemical changes in the water. Here are a couple of web pages with more information about the hyporheic zone:

Finally, a lot of filtering takes place as water moves through the ground, through soil, the unsaturated zone (where both water and air fill the pore spaces, or spaces between soil particles), and in aquifers (where water alone fills the pore spaces). Large particles, such as silt, leaves, and twigs are filtered out because they can't fit through the small pore spaces. Smaller particles such as suspended clay and microorganisms become adsorbed (get stuck) onto soil particles. Some microorganisms are eaten by other organisms. And some dissolved chemicals such as nitrates and pesticides are taken up by bacteria that live underground. This doesn't mean that all chemical or microbiological pollutants are filtered out of ground water--untreated ground water can in some cases contain harmful pollutants. But ground water is usually cleaner than surface water. The natural filtering process that removes pollutants from ground water is sometimes called "natural attenuation". Here is a web page about a report on the topic:

Some cities use the natural filtering ability of aquifers as a way to help treat their public water supplies. They put large wells along the banks of a river, or even under the bottom of the river. The river water flows through the ground on the way to the well, and undergoes some filtration in the hyporheic zone and the aquifer, on the way to the well. This is called riverbank filtration. Many European cities have been using riverbank filtration for 50 years or more, and it is becoming popular in this country, as well, in places like Cincinnati, Ohio; Lincoln, Nebraska; Louisville, Kentucky; and Parkersburg, West Virginia.

There are even some cities where clean natural water is so scarce that treated sewage is reused by filtering it through the ground.

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24.Q: Where can I get information on water purification techniques?

A: A good source of information on home drinking-water treatment technology and performance of specific products is NSF International, which offers a listings database for products on their Consumer Information page.

25.Q: Can you define safe water?

A: Safe water means water that will not harm you if you come in contact with it. The most common use of this term applies to drinking water, but it could also apply to water for swimming or other uses. To be safe, the water must have sufficiently low concentrations of harmful contaminants to avoid sickening people who use it. The list of harmful contaminants includes disease-causing microbes such as bacteria, viruses, and protozoans; cancer-causing chemicals such as many pesticides, organic solvents, petroleum products, chlorinated byproducts of the disinfection process, and some metals and metalloids; nitrates and nutrients, endocrine-disrupting compounds, strong acids, strong bases, radionuclides, and any other acutely toxic substance. Defining safe water becomes a matter of risk assessment, in which you consider the chance of illness or injury from drinking the water, in comparison to the risk of illness or injury from the many other hazards in our lives,for example, riding in a car, or breathing the air, or shaking hands, or exposure to radiation from the sun, or to contaminants in the food we eat. In comparison to such other activities, drinking U.S. public tap water, or any of the bottled waters, or water from most domestic wells, is very safe indeed. These waters might come from wells or springs that tap shallow or deep aquifers, from rivers or lakes, or glaciers, or even from rain-water collectors, fog collectors, or from desalinated sea water. Most of these waters are filtered and treated to kill microbes and keep contaminants at safe levels.

How do you define "safe levels"? The U.S. Environmental Protection Agency (EPA) sets Maximum Contaminant Levels (MCLs) for many harmful contaminants, based on health-effects research, contaminant occurrence data, economic analysis, and risk analysis. The MCLs for currently regulated drinking-water contaminants are listed on EPA's Office of Ground Water and Drinking Water Web page under "Drinking water standards program."

Keep this in mind: water that is safe for one person may be unsafe for another. If your immune system is weakened by HIV/AIDS, or by a recent bone-marrow transplant, or if you are a young child or an elderly person, or pregnant or a nursing mother, you are more susceptible to contaminants in drinking water than the rest of the population. Your doctor may urge you to take extra precautions with the safety of your drinking water. An online reference is EPA/CDC's guidance for people with severely weakened immune systems.

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26.Q: Where can I find detailed sampling methods for surface water and ground water?

A: USGS protocols for the collection of ground-water and surface-water samples have been published in the report National Field Manual for the Collection of Water-Quality Data.. The National Field Manual was published in chapters, and copies of this Techniques of Water-Resources Investigations, Book 9, handbook can be ordered by calling 1-888-ASK-USGS or at Ordering U.S. Geological Survey Products.

27.Q: If the sulfur content in my well water is a little high, is it still safe to drink?

A: Sulfur is not regulated as a primary drinking-water contaminant, so there is no official level of sulfur that represents a threshold between healthy and unhealthy concentrations. Sulfur is required by all living things as part of their normal metabolism, so the body needs a certain amount of sulfur just to live. Any adverse effects of sulfur in drinking water appear to be related to the following issues:

  1. Hydrogen sulfide (H2S) is sometimes present in well water. A few tenths of a milligram of hydrogen sulfide per liter can cause drinking water to have a rotten-egg odor. While unpleasant, it is not harmful to health. (See Question 20 on this web page, which discusses odor and smell.)
  2. High concentrations of sulfate (SO4--) may be associated with diarrhea. For this reason, and for aesthetic reasons related to taste and odor, the Environmental Protection Agency currently has a secondary drinking-water standard of 250 milligrams per liter (mg/L) sulfate. Further information on sulfate and drinking water can be found at this web site:
  3. Some waters with elevated sulfate also tend to have low pH (as in acid mine drainage). The pH of water is usually checked when well water is tested. A pH between 6.5 and 8.5 is in the range recommended by EPA.

Bottom line: If you are not bothered by a rotten-egg odor, and you don't have a sulfate concentration over 250 mg/L, you should have nothing to worry about from the sulfur.

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28.Q: Whom do I contact to have my well water tested?

A: You can contact your county or state health department or check with your State Certification Officer for a list of state certified laboratories in your area that do water testing. The cost will vary, depending on the laboratory and the test(s), but people usually consider the cost to be reasonable.

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29.Q. What are the permissible levels of trace elements (such as arsenic, copper, iron, lead, and zinc) in water for the water to still be considered safe for exposure/bioaccumulation by people and aquatic life?

A: Several of these trace elements are regulated by the EPA and are on their list of primary drinking water standards. These include arsenic, copper, and lead, as well as cadmium, chromium, mercury, and selenium. Iron is not a regulated contaminant because it is not known to cause health problems, but there is a secondary drinking water standard based on its tendency to stain laundry and plumbing fixtures. Manganese, copper (again), silver, and zinc are also included in the secondary standards. The primary and secondary standards are available on the EPA Web page Current Drinking Water Standards.

The above standards are national drinking water standards. Other water-quality standards are set by states to protect aquatic life. You can check with your state environmental or natural resources agency to see what aquatic life water-quality standards are in effect in your state. EPA is currently reviewing its recommendations for aquatic life criteria. Information on the current review of standards is available on Aquatic Life Water Quality Criteria.

The USGS National Analysis of Trace Elements also has current information on trace elements across the United States, including links to specific studies and current items in the news.

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