Can I test my own well water for coliform bacteria at home?

Health authorities strongly recommend an annual coliform bacteria water test for private water wells, as contamination can occur without any change in taste or odor to the water. Private well owners are responsible for ensuring their water is safe, as public water regulations do not apply to private water systems. There are many ways that well water can become contaminated by coliform bacteria, but it is most important to test:

• Once a year for all private water systems, including private residential water wells
• After a new well has been constructed
• After recent work has been done on the well
• If you suspect or see any indication that contamination has taken place, such as if the well was covered with flood water.

The Environmental Protection Agency (EPA) provides guidelines for water testing and safety for both public and private water sources.

Understanding Coliform Bacteria in Well Water

Well water typically contains two categories of coliform bacteria: total coliform and fecal coliform (including E. coli).

Total coliforms occur naturally in the environment—in soil, surface-influenced water, and human or animal waste. While their presence alone doesn’t confirm contamination, it often signals that more harmful bacteria, such as fecal coliform or E. coli, may also be present.

Fecal coliforms, a subgroup of total coliforms, live in the intestines and feces of warm-blooded animals. They serve as a stronger indicator of contamination from human or animal waste than total coliforms alone.

Escherichia coli (E. coli) is the major species in the fecal coliform group and is considered to be the best indicator of fecal pollution and the possible presence of pathogens. Most coliform bacteria do not cause disease.

However, some rare strains of E. coli, particularly the strain 0157:H7, can cause serious illness. Recent outbreaks of disease caused by E. coli 0157:H7 have generated much public concern about this organism. E. coli 0157:H7 has been found in cattle, chickens, pigs, and sheep. Most of the reported human cases have been due to eating undercooked hamburgers. Cases of E. coli 0157:H7 caused by contaminated drinking water supplies are rare.

There are many ways that well water can become contaminated, so it is important for private well owners to regularly test water for coliform bacteria and other contaminants to ensure safety.

What Should I Test For?

Testing for bacteria is the only reliable way to know if your water is safe. You cannot tell by the look, taste, or smell of the water if disease-causing organisms are in it. Coliform bacteria are a large group of bacteria, some of which can indicate the presence of dangerous pathogens. Well-owners should test their water for coliform bacteria at least once a year and more frequently if bacteria have been a problem in the past.

Frequently, concentrations of pathogens from fecal contamination are small, and the number of different possible pathogens is large. As a result, it is not practical to test for pathogens in every water sample collected. Instead, the presence of pathogens is determined with indirect evidence by testing for an “indicator” organism such as coliform bacteria. Indicator bacteria are used because testing for all disease-causing organisms is impractical.

The most basic test for bacterial contamination of a water supply is the test for total coliform bacteria. Total coliform counts give a general indication of the sanitary condition of a water supply. The presence of indicator bacteria suggests the possible presence of disease-causing microorganisms.

Which Test Kit Do I Need?

The at-home test is an easy, fast, and effective method for determining whether your well water contains coliform and E. coli. This simple test causes the media to turn blue-green in the presence of coliform bacteria. Water samples should be collected carefully using proper bottles and procedures to ensure accurate results.

We recommend the EPA-compliant Coliform Bacteria EZ Cult 24-Hour Presence / Absence of Total Coliforms test. This simple test shows that the media inside the bottle turns blue-green in the presence of coliform bacteria. E. coli growth is confirmed by blue fluorescence under UV light. Having your water tested regularly helps ensure the ongoing safety of your well water.

The UV is not included but can be purchased separately if you also want to test for E. coli bacteria.

How to Collect a Water Sample for the WaterCheck

Before collecting a sample, make sure your well pump is operating properly to avoid inaccurate results.

1: Prepare to Collect the Sample

• Wash your hands with soap and warm water.
• Use a frequently used indoor tap, like a kitchen faucet.
• If the tap has a screen, remove it before collecting the sample.
• Run cold water for at least 2 minutes to flush the line.

2: Collect the Water Sample

• Hold the bottle near the base of the tap.
• Fill it past the 200 mL mark (to the shoulder), but don’t overfill.
• Cap the bottle immediately—secure it tightly but avoid over-tightening.
• Apply the identification label from the requisition form to the bottle.

3: Complete the Requisition Form

Include the following information:

• Your name and daytime phone number
• Mailing address and postal code
• Collection site (e.g., kitchen sink)
• Legal land description or civic address
• Date and time of sample collection
• Name of the person who collected the sample
• Whether it’s a re-sample
• Complete Section A (Drinking Water)
• Add comments or special requests if needed

4: Pack and Transport the Sample

• Place the sample and completed requisition form in the provided plastic bag.
• Put the sample in a cooler with ice packs.
• Deliver it immediately to a local drop-off site or send it via overnight/next-day express shipping.

Important Sampling Tips

• Always collect from the cold water supply line.
• Never rinse the sampling bottle.
• Don’t let water splash down the side.
• Keep the cap off the counter and avoid touching the inside.
• Don’t open the bottle until you’re ready to collect the sample.
• Avoid collecting from garden hoses, outdoor taps, or any dirty source.

Note: Shallow wells are more vulnerable to contamination, which can affect your test results.

When Should I Test and How Often?

Late spring or early summer is the best time to test your well since coliform contamination is most likely to show up during wet weather. Shallow wells are at higher risk of contamination compared to deep wells, due to their proximity to the surface and limited filtration through soil layers. Deep wells, typically over 100 feet, are less likely to be contaminated by surface bacteria. Whether your test results are positive or negative, understand that the sample you collected is just a “snapshot” of your well’s water quality. The more samples you have tested, the more confident you can be about the quality of the water you are drinking.

What Do The Results Mean?

If coliform bacteria are present in your drinking water, your risk of contracting a waterborne illness is increased. Although total coliforms can come from sources other than fecal matter, a positive total coliform sample indicates the possibility of pollution in your well. Some possible causes of contamination include surface runoff, septic system failure, or animal waste entering the well.

Positive results for fecal coliform bacteria, especially positive E. Coli results, indicate contamination from human or animal waste and should be taken seriously as they signal fecal pollution in your well.

Consuming contaminated water can lead to a range of diseases, from mild gastrointestinal illness to more severe conditions.

Steps to Take When Coliform Bacteria Are Found in Your Well

Begin with emergency chlorination, which typically lasts two to five days, if tests detect E. coli or fecal coliforms in your drinking water. Disinfect the well system to eliminate harmful bacteria. Use shock chlorination—a widely recommended method for treating bacterial contamination. While disinfecting, boil all water for drinking and cooking vigorously for at least one minute before use.

It is also very important to continue testing the water because if anything happens to the chlorine residual or if the chlorine demand changes and the consumer doesn’t know about it, the water can become unsafe again. However, if fecal coliforms or E. coli are detected in well water, the first step should not only be to disinfect your system but also to identify the source of your bacteria contamination.

Installing a water treatment system can provide ongoing protection against bacterial contamination.

What Kinds of Defects Can Allow Contamination?

Improper well construction is a leading cause of well contamination, as faulty wellheads, poor sealing, or inadequate construction practices can allow contaminants to enter the water supply.

• Cracked or missing well caps may allow contaminants to enter through unsealed areas around wires, pipes, or where the cap meets the casing.
• Cracks or holes in the well casing can let unfiltered water seep directly into the well—this is especially common in wells made of concrete, clay tile, or brick.
• Contaminants can seep along the outside of the casing when wells lack proper grout sealing, which is often the case with older constructions.
• Floodwater can infiltrate wells located in frost pits below ground, especially during wet weather.
• Improperly maintained or poorly placed septic systems can release coliform bacteria and other pollutants into nearby groundwater.
• Heavy rain or flooding can carry surface bacteria into wells, particularly if the well is shallow or constructed improperly.

Human activities, such as agriculture or improper waste disposal, can also contribute to well contamination. Soils play a role in filtering contaminants before they reach the well, but their effectiveness depends on soil type and condition.

Long-Term Options for Dealing with Bacterial Contamination of a Well

• Connecting to the regional public water system, if possible
• Inspecting wells for defects and repairing them if possible
• Constructing a new well
• Installing continuous disinfection equipment
• Using bottled water for drinking and food preparation