The National Ground Water Association (NGWA) recommends well owners test their water at least annually for bacteria, nitrates, and any contaminants of local concern. More frequent testing should be considered if:

  • There is a change in the taste, odor, or appearance of the well water, or if a problem occurs such as a broken well cap, inundation by floodwaters, or a new contamination source
  • The well has a history of bacterial contamination
  • The septic system has recently malfunctioned
  • Family members or house guests have recurrent incidents of gastrointestinal illness
  • An infant is living in the home, or
  • To monitor the efficiency and performance of home water treatment equipment.

Check with your local health or environmental health department for recommendations regarding the type and frequency of testing specific to your location. For help in interpreting your water test results—and what might be a health risk or an aesthetic issue—ask the lab that conducted the test or your county health department.

Total coliform is the most commonly used indicator of bacterial contamination. The presence of coliform bacteria is an “indicator” of a well’s possible contamination from human or animal wastes. Total coliform are a broad category of bacteria, most of which pose no threat to humans. Some come from fecal matter; others naturally occur in soils, vegetation, insects, etc. The presence of coliform bacteria in well water can be a harbinger of worsening water quality. In some cases, more specific tests for fecal contamination, such as E.coli, may be used.

Common sources of nitrate to well water are fertilizers, septic systems, animal manure, and leaking sewer lines. Nitrate also occurs naturally from the breakdown of nitrogen compounds in soil and rocks. High levels of nitrate in well water present a health concern and can also indicate the presence of other contaminants, such as bacteria and pesticides. Drinking large amounts of water with nitrates is particularly threatening to infants (for example, when mixed in formula).

Typical additional tests are those for pH, hardness, iron, manganese, sulfides, and other water constituents that cause problems with plumbing, staining, water appearance, and odor. Changes in these constituents also may indicate changes in your well or local groundwater. Additional tests may be recommended if water appears cloudy or oily, if bacterial growth is visible on fixtures, or water treatment devices are not working as they should. Check with your water well contractor, state department of natural resources, or local health department for information on local water quality issues.

Your state may recommend or require testing for certain contaminants specific to your locality. Arsenic and radon are two examples of water-quality concerns in certain areas. Arsenic occurs in water that comes into contact with some types of rocks and soils. Radon is a colorless, odorless, and tasteless gas that comes from the natural radioactive breakdown of uranium in the ground. Exposure to radon can come from two sources: the air in your home, which seeps up through the foundation, and your well water. (Note: Arsenic and radon are used here as examples only, and may or may not be a problem in your area. Check with your state or local health department.)

To find state requirements or recommendations for well water testing, visit our State Contacts page.

Often county health departments do water tests for bacteria and nitrates. If you want to test for other substances in the water, the county health department should be able to provide a list of area state-certified drinking water testing labs. Your State Laboratory Certification Officer also can provide a list of certified drinking water testing labs. To find a certified water testing laboratory in your area, visit this page on the U.S. EPA Web site,, or call the toll-free Private Well Owner Hotline at 855-420-9355.

Ask the lab that will be doing your water test for instructions on how to collect the water sample and for sampling bottles. Follow the instructions carefully to get accurate water test results.

While a well owner can take samples with due care and instructions, in some cases, it is better to have a qualified person, such as a technician from the laboratory, do the sampling. It is easy to contaminate coliform samples and sampling for some analyses such as volatile organics or methane have specific technical requirements.

It also is important to follow advice about storing the samples. Ask the lab how soon the samples must be taken to the lab for testing. These instructions can vary depending on the substance.

Well owners sometimes find laboratory water test results confusing. It is particularly important to know if anything in the test results indicates a health risk. In some cases, the testing lab will give a very helpful explanation. If not, the following may be able to help:

  • The local health department or agricultural agent
  • • An online water test interpretation tool. To try one, click here
  • The state drinking water program, which is often part of the state’s health or environmental department
  • The state agency that licenses water well contractors.
  • The Private Well Owner Hotline at: (855) 420-9355 or (855) 420-9355 FREE

Health risks can vary based on several factors. Key factors in the amount of risk from a drinking water contaminant are the specific substance and the amount of that substance in the water. Another factor is the health or in some cases the age of the person. For instance, very young children who take in high levels of nitrate over a relatively short period of time can experience dangerous symptoms while an adult would not.
Other contaminants pose a long-term or chronic threat to one’s health due to small amounts consumed regularly over a long period of time.

Well owners can get guidance from U.S. EPA drinking water rules for public water systems, which are designed to protect people from both short- and long-term health hazards. The amounts of contaminants allowed are based on protecting people over a lifetime of drinking water. Private well owners can compare their test results to these federal or state drinking water standards to determine whether their test results represent any health risks.

You can find the federal Maximum Contaminant Levels at

If after any necessary well maintenance water test results still indicate a health risk, check with your water well system professional or a water treatment service provider about appropriate treatment technologies. A treatment system’s specifications should indicate whether that system is designed to treat a specific contaminant at the concentration it exists in the water.

You can find more information on water treatment at the National Sanitation Foundation,, or the Water Quality Association Website at

A qualified groundwater professional familiar with microbiological water quality (may be a water well system contractor, hydrogeologist, or microbiologist) can determine if your water well system needs cleaning by conducting an anaerobic bacteria test, a coliform test, or other biofouling indicator tests that can indicate an accumulation of debris in the well. Anaerobic bacteria can be an indicator of overall bacterial activity in the well—including possible harmful bacteria. However, some wells are naturally anaerobic. A qualified groundwater professional can advise on the type of testing or inspection indicates that well sanitation or biofouling are issues to correct. While most coliform bacteria are not harmful, they serve as indicators of possibly harmful bacteria. The water well contractor also will inspect the general condition of the well in determining whether to clean the well.

A qualified water well system contractor is equipped to properly clean your water well. Well cleaning may require removing debris from the well bottom or cleaning other components of the well. The contractor may brush and clean the well casing to remove any accumulation of solid material and flush the gravel pack and aquifer surrounding the well casing.

Water intakes may likewise be brushed and cleaned. Open borehole wells can be cleaned by carefully jetting the borehole walls to loosen the debris, which then can be evacuated from the well.

Any water treatment devices that are part of your water well system should be checked and serviced according to specifications. A water treatment device that is not regularly maintained can harbor harmful bacteria.

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