Private Well Water


Private Well Water

Frequently Asked Questions

Public drinking water systems are required by federal regulations to test for various contaminants at specified intervals to ensure the water is safe for human consumption. Because private wells are not subject to these mandated regulations it is up to well owners to monitor the safety of their drinking water by testing the water for coliform bacteria and nitrate on a regular basis.

What should I test for?
How often and when should I test?
Are there any exceptions?


How do I collect a sample?
What is the white powder in the coliform sample bottle?
Where should I collect my coliform and nitrate samples?
Can I submit ANY container for coliform and nitrate?
I do not live in Iowa. May I still order and send you a sample?
Can you test for other contaminants from the coliform and nitrate sample bottles?
Should I request numbers for the coliform test instead of just presence or absence?
How full does the container need to be?
How soon do you need to receive the samples?

What Should I Test for?

Generally, it is not cost effective or necessary to test for all possible contaminants that may be present in well water. Under normal circumstances, testing for coliform bacteria and nitrates will give you a general indication of the sanitary quality of your drinking water. However, if there are extenuating situations, (e.g. pesticide spill near the well or a back-siphoning accident), you will need to test for that specific contaminant.

How Often and When Should I Test?

SHL recommends that private well testing for coliform bacteria and nitrates occur at least once each year in the spring or fall (rainy season), or anytime changes occur in taste, odor or appearance.

Are There Any Exceptions?

Testing more frequently for coliforms and nitrate, and other potential contaminants, may be necessary if the well is located near a possible source of contaminants such as livestock confinement areas, septic system/laterals, sanitary landfills, industrial or manufacturing activities or agricultural fields, or if the well is susceptible to flooding. Additional testing for other contaminants may also be necessary if a hazardous material spill near the well or a back-siphonage event has occurred. More frequent testing is also recommended for shallow older wells that may not be constructed according to current well construction regulations for non-public water supply wells. If you have questions about what to test for, please contact our laboratory for assistance.


How do I collect a sample?

Directions for collecting a sample for coliform bacteria and nitrates are included in the collection kit, along with specially-prepared sterile bottles. If you asked for coliform bacteria and nitrate testing, you will receive two bottles: one for coliform bacteria and one for nitrates. Please follow the instructions carefully; it is easy to contaminate the sample WITH coliform bacteria using IMPROPER sample collection techniques.

What is the white powder in the coliform sample bottle?

The white powder is a chlorine-neutralizing agent since some well water is chlorinated. Neutralizing any chlorine is necessary to obtain a valid coliform test. The agent will not interfere with the coliform analysis even if chlorine is not present. However, this chemical can interfere with the nitrate test so the sampling bottle for this test does NOT contain this agent.

Where should I collect my coliform and nitrate samples?

Where the sample is collected depends on the purpose for sampling. In general, the sample should be collected from the tap most frequently used for drinking water.

If you are troubleshooting a coliform bacteria problem, you may need to collect numerous samples at strategic locations in your system as outlined in the coliform action response flowchart Sampling locations may include various areas of the distribution system. These include near the well, at the connections from the well and at points before and after water treatment devices. This approach helps determine the source of the coliform bacteria problem so that appropriate remedial action can be taken to eliminate the organisms.

Can I submit ANY container for coliform and nitrate?

No. The coliform and nitrate bottles are specially prepared for this testing. You must use the container supplied by the laboratory for the purpose intended.

I do not live in Iowa. May I still order and send you a sample?

Yes, sampling kits for coliforms and nitrate can be sent outside of Iowa. However, the sample must be received by the laboratory within 48 hours of sample collection.

Can you test for other contaminants from the coliform and nitrate sample bottles?

No. The State Hygienic Laboratory can test for a variety of organic, inorganic, radiological and microbiological contaminants in drinking water. Each contaminant will require its own type of container, sample volume or preservative. The laboratory can help determine what tests are necessary based on your circumstances and needs.

Should I request numbers for the coliform test instead of just presence or absence?

Requesting that your coliform result be reported in numbers (called Most-Probable- Number or MPN) is usually not necessary if you are collecting only one sample and you just want to know if your water is safe to drink. If you are troubleshooting a coliform problem and collecting numerous samples to pinpoint the problem, numbers may be helpful in that situation. Because of the uneven distribution of bacteria in a water system, the most probable number is only a semi-quantitative estimate of the number of bacteria in the water sample. You can only compare the numbers in ballpark terms; for example, total coliform MPN results of 20 and 40 are considered similar for bacteria testing.

How full does the container need to be?

Fill both containers to the shoulder of the bottle-- between the 100mL-mark on the bottle and the threads on the neck on the bottle. The laboratory needs 100mL for testing and also some air space to facilitate proper mixing.

How soon do you need to receive the samples?

The sooner you can get the samples to the laboratory, the more accurate the test results will be. The required time between collection and receipt at the laboratory is 48 hours, so mail or ship samples the same day of collection to avoid delay. Also, avoid Friday, weekend and just prior to holiday mailings.

Testing and Result Interpretation

How long does the testing take? When and how will I get my results?

The turnaround time depends on the test requested. For example, results for coliforms and nitrates are usually available in 2-3 days, radiological results may not be available for several weeks.

Test results are routinely sent via mail. Upon request, results may also be phoned or faxed.

How do I interpret my results?

Coliform Bacteria and E.coli:

If the total coliform bacteria and E.coli test results are “ABSENT” or the most-probable-number is listed as “<1,” these results are satisfactory and the water is bacterially safe for drinking purposes. If the total coliform bacteria test is “PRESENT” or the number is greater than or equal to 1 (e.g. 1, 2, 3.1, 5.6, 200.5, etc), this result is UNSATISFACTORY and indicates the water is bacterially UNSAFE and should NOT be used for drinking unless properly disinfected before use (e.g. boiling for one minute). In addition, if the E.coli bacteria test result is also “PRESENT” or the number is greater than or equal to 1 (e.g. 1, 2, 3.1, etc), this result indicates the water may be contaminated by human or animal sewage. The presence of E.coli indicates that the water may be contaminated with microorganisms that CAN cause disease and thus represents a serious health concern.


Nitrate levels in water samples above 45mg/L (reported as nitrate or NO3) or above 10mg/L (reported as nitrate-nitrogen or as N) are considered unsafe for infant consumption and should NOT be used to prepare formula or used for drinking by infants less than six months of age. These levels pose a health risk to bottle-fed infants by reducing the oxygen-carrying capacity of the blood (a rare disorder called methemoglobinemia, also known as nitrate cyanosis or blue baby syndrome). High nitrates in drinking water suggest that other contaminants may be present or have an opportunity to enter the drinking water supply. Therefore, the source of the nitrates and how they may have entered the system should be investigated.

If my water is unsafe for drinking, whom do I call for help?

County health department personnel and certified well drillers/installers can assist you in determining possible sources of contaminants and how they entered the system, and can recommend remedial procedures.

Whom do I call for help with result interpretation?

Your local county health department personnel and State Hygienic Laboratory staff are available to help with result interpretation.

What are total coliform bacteria?

Total coliform bacteria are microorganisms that are present in soil and sewage and thus are present in all surface water and very shallow groundwater that is under the influence of surface water. As surface water percolates through the soil, a natural filtration process takes place which normally removes microorganisms (including coliform bacteria) UNLESS a pathway exists which bypasses this natural filtration process. The presence of coliform bacteria in drinking water indicates a possible sanitary defect in the drinking water system that could provide a pathway of entry for contamination into the well OR distribution system (plumbing into the home). This pathway may provide an opportunity for harmful material to enter the drinking water creating a potential health hazard.

What are E.coli bacteria?

Escherichia coli (E.coli) bacteria are a group (subset) of total coliform bacteria which are present in sewage material. The presence of E.coli bacteria in drinking water indicates a pathway (defect) exists from a relatively fresh waste source such as an animal feedlot, septic tank,cesspool leadage, etc. Their presence also indicates that the water may be contaminated with microorganisms that can cause disease which represents a serious health concern. Drinking water which contains E.coli should NOT be used for human consumption unless properly disinfected before use.

My water sample is positive for total coliform bacteria. Will I get sick?

By themselves, total coliform bacteria will not make you sick. However, the presence of coliform bacteria indicates a sanitary defect in the well or distribution system and thus represents a potential health hazard if the water sample was correctly collected and accurately represents the drinking water.

What are nitrates?

Nitrogen is an element that occurs naturally in the environment and is essential for living matter. All sources of nitrogen are potential sources of nitrate. Nitrate is a chemical compound composed of nitrogen and oxygen. Nitrate concentrations exceeding the infant health advisory level of 45 mg/L as NO3 or 10 mg/L as N are generally an indication of contamination from major nitrogen sources such as sewage disposal systems, animal manure or nitrogen fertilizers. Nitrate contamination is more likely to occur in shallow wells and in wells which are poorly located, constructed or maintained.

How can nitrates be removed from drinking water?

Nitrates can be removed from drinking water with distillation, reverse osmosis or anionic exchange. Please refer to Well Water Quality and Home Treatment Systems for more details.

How do I trouble-shoot a coliform bacteria problem?

Follow the suggestions listed on the SHL coliform response flowchart. First review the sample collection procedure. If the sample was collected correctly and represents the drinking water supply, then an inspection of the complete water system (well and distribution plumbing system) and area surrounding the well should be made to search for the sanitary defect or pathway. Then that defect should be corrected accordingly. Strategic sampling for coliform bacteria (in the most-probable-number (MPN) result format) collected at various locations (e.g. at the well, before or after treatment systems, etc.) may be necessary to pinpoint the source of the problem. For example, if the samples taken closest to the well and before the softener are negative and the sample after the softener is positive, this indicates that the softener may be contaminated (e.g.biofouled) and is the source of the problem.

With older wells, this defect may include structural problems in the well such as pits, cracks in the casing, inadequate grouting, brick or concrete wells, or cisterns.

With new wells, the defect is more likely a problem with the distribution system such as cross-connections, broken or contaminated distributions lines or treatment systems, faulty pressure tanks, contamination from repairs or new construction WITHOUT proper disinfection, etc.

A sanitary survey of your water system and remediation assistance may be available from your local county health department or certified well driller and pump installers.

Can I boil my water to make it safe?

If your water is bacterially unsafe due to coliform bacteria or E.coli, the water can be disinfected by boiling for one minute. This high temperature will kill all microorganisms that could be in the water. Other safe drinking water alternatives include bringing water from a known safe source such as city water or buying bottled water for drinking purposes. Remember to use very clean drinking water containers for water transport or storage. Do NOT use containers that have been used for food or milk since these containers are very difficult to get clean for this purpose. Caution: Boiling for an extended period of time may concentrate chemical contaminants.

Can I wash dishes, brush my teeth or take a shower in bacterially unsafe water?

The total coliform bacteria standard was developed primarily for drinking purposes. The risk of illness from using this water for any of these other activities is not as clear cut. Since you may need to use this water for these other activities while you are investigating your coliform problem, there are some options. For washing dishes, dishwashers can be set on sanitation cycle, or one can manually pour boiling water over dishes and utensils. Drinking water used for brushing teeth should be of safe water quality (e.g. boil water for one minute, bring water from a safe source, or buy bottled water). Showering with water that is bacterially unsafe (total coliform positive, E.coli negative) has a far lower risk of illness than drinking this water. If the bacterially unsafe water is due to E.coli which indicates a sewage contamination source, using this water for any activity other than flushing the toilet is not recommended.

What should I do if flood waters cover my drinking water well?

Because flood water is contaminated with microorganisms that can cause disease, you should NOT drink the water. Wait until the flood waters recede, then contact your local county health department or certified well driller/pump installer for well shock-chlorination guidance. Perform this procedure (include flushing the well) BEFORE submitting a sample to the laboratory to make sure your drinking water is now safe (total coliform and E.coli absent). Shallow wells (less than 100 feet deep) may become contaminated from nearby flooding. They should be tested to ensure a safe supply of drinking water.