If you get your water from a private source, such as a well or spring, you are responsible for ensuring that your drinking water is safe. You are the regulator, inspector, maintenance manager, accountant and consumer.
How safe is well water?
Generally, the groundwater pumped from wells is safe to drink. As water moves through layers of soil to reach the underground aquifer, disease-causing organisms, such as bacteria and viruses, are filtered out or eaten by soil microorganisms. Many harmful chemicals, such as pesticides, are also broken down in the soil before they reach the aquifer that supplies your drinking water. Exceptions occur when:
- Wells are not properly constructed or maintained.
- Wells indirectly draw water from surface water sources.
- Wells draw water from unconfined aquifers in areas where there have been potentially contaminating land uses (such as chemical spills, a large number of septic systems, intensive agriculture or construction).
What should I look for to make sure my well is properly constructed and maintained?
In addition to checking the inspection points shown in Figure 1, make sure your well is sealed with cement or bentonite clay to a depth of at least 18 feet. For more information on this and other well-safety topics, review your well log and the Oregon Water Resources Department’s Water Well Owner’s Handbook. For most wells, well logs can be found at the Oregon Water Resources Department website
How do I know if my well water is safe to drink?
It is impractical for people with individual water systems to test for all possible contaminants. Instead, testing every one to three years for coliform bacteria and nitrate will give you a good indication of the overall condition of your water supply. If any change is noticed in the color or taste of your water, test immediately for coliform bacteria.
The first time you test your well, you should also test for arsenic to identify its presence and levels. If arsenic is present in an initial test and the level is above 8 parts per billion, you should retest. If high concentrations continue, a treatment system should be installed.
Many drinking-water labs offer a suite of tests for well owners. If you have a reason to suspect specific problems, such as a leaking underground fuel tank, pesticide spills or other contamination of concern, you may want to expand your water-quality testing. Choose a state-certified, water-quality laboratory to test your drinking water for contaminants of concern. Your Oregon State University Extension Service county office or the Oregon Health Authority can provide lists of these labs.
What does a positive test for coliform bacteria mean?
Coliform is a group of bacteria found almost everywhere, but it does not occur naturally in groundwater. Coliform bacteria in your water indicates that above-ground contaminants have reached your water supply. The contaminants may have come from surface water leaking down your well, objects entering an open well, or a shallow water source. Coliform bacteria generally does not cause disease, but when it occurs, it indicates the possible presence of other disease-causing bacteria, such as certain strains of fecal coliform. Fecal coliform naturally occurs in the intestines of healthy, warm-blooded animals, such as humans, dogs, deer, cattle, horses and ducks.
Fecal coliform in drinking water means that the water has come in contact with human sewage or other animals’ waste. Some fecal coliform bacteria, such as certain strains of Escherichia coli (E. coli), can cause severe illness. If you have unexplained symptoms of intestinal illness, have the water tested to see if E. coli or other harmful microorganisms are in your drinking water.
What can I do about coliform bacteria in my well?
- Do not drink the water unless you boil it for 3 minutes to kill the bacteria.
- Shock chlorinate your well to kill all bacteria. Retest before using. If you have arsenic in your well, shock chlorination can temporarily increase levels of arsenic.
- Try to identify the source of the contamination.
- Repair your well, if needed.
- Divert surface water from the wellhead.
- If you are unable to get clean test results, treat your water using a chlorination or UV system.
- Consider connecting to a public water system, if available.
What can I do if fecal coliform or E. coli is in my well?
As described above, if fecal coliform or E. coli is in your water, there is a direct connection between your drinking water and the intestines of a warm-blooded animal and all the diseases they can transmit. Follow the instructions above for boiling your water or find an alternative source of water until you are able to identify and correct the source of the human or animal waste, and ensure that it does not continue to reach your well.
What does the presence of nitrate indicate?
Nitrate (NO3-N) is a form of nitrogen used by plants. It is found in fertilizers and animal wastes. Other forms of nitrogen in the soil also are converted to nitrate. Water carries nitrate through the soil very easily. If there is more nitrate in the soil than plants can use, the extra is washed downward, eventually reaching the water table.
If nitrate is found in your well water, it means that:
- There is a source of excess nitrogen in the vicinity, such as agriculture, fertilized lawns, septic systems, animal waste or a combination of these sources.
- Your water is coming from an aquifer that has some surface to groundwater interaction and, therefore, may be affected easily by other contaminants leaching through the soil.
Is it safe to drink water with nitrate in it?
Nitrate levels of up to 3 parts per million may be naturally occurring in well water or may indicate some low level of contamination, but are considered safe for consumption. The Environmental Protection Agency has set a maximum contaminant level of 10 parts per million for nitrate for drinking water. Nitrate levels near or above 10 parts per million may pose a serious health concern for infants, pregnant or nursing women, or other immune-compromised individuals. Nitrate can interfere with the blood’s ability to carry oxygen to vital tissues in infants 6 months old or younger. The resulting illness is called methemoglobinemia, or “blue-baby syndrome.” Make sure to talk with a medical professional about how your well’s water quality could affect the health of you and your family.
Little is known about the long-term effects of drinking water with elevated nitrate levels. Some research suggests that nitrate may play a role in spontaneous miscarriages, thyroid disorders, birth defects, and in the development of some cancers in adults. Recent human epidemiologic studies show that nitrate ingestion may be linked to gastric or bladder cancer. An additional concern when nitrate is present in drinking water is the potential for other chemical contaminants to reach the water along with the nitrate.
What can I do if nitrate levels are elevated in my well?
- Identify the potential sources of nitrate and find ways to manage them. Contact your OSU Extension Service county office or your Soil and Water Conservation District office for more information.
- Examine your property and the surrounding area for sources of other contaminants (for example, fuels, specific pesticides, bacteria). Test for these items if you think your water may be at risk.
- Monitor your nitrate levels regularly and keep all screening records.
- If you choose to treat your water to remove nitrate, use reverse-osmosis or ion-exchange systems. Boiling water does not remove nitrate but instead increases the concentration.
For more information
OSU Extension Service resources
- Oregon State University Well Water Program
- Twelve simple things you can do to protect your well water / Doce pasos sencillos para proteger su agua de pozo (EM 8651)
Other resources
- Oregon Water Resources Department
- Oregon Health Authority Domestic Well Safety Program
- Oregon Department of Environmental Quality
- National Environmental Laboratory Accreditation Management System for listings of accredited water-testing laboratories.
- Environmental Protection Agency — Private Drinking Water Wells
- U.S. Geological Survey — Water Resources
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