One in five private wells in the United States may contain at least one contaminant at levels exceeding a primary drinking water standard set by the EPA (U.S. Geological Survey, 2013). That's a pretty strong chance your well water might have something unwanted in it, and often, that something is bacteria.
For many homeowners, the thought of bacteria in their drinking water is unsettling – and for good reason. From subtle gastrointestinal issues to serious illnesses, waterborne bacteria can pose significant health risks, especially to children, the elderly, and those with weakened immune systems. This isn’t just about making your stomach rumble; it can be about serious health emergencies. So, let’s dig into what finding bacteria in your well means, particularly coliform and the dreaded E. coli, and what you can do about it.
When your well water gets tested for bacteria, two terms will almost certainly come up: “total coliform” and “fecal coliform” (or E. coli). It’s important to understand the difference because it dictates your next steps. Think of it like this: all squares are rectangles, but not all rectangles are squares. All E. coli are coliform, but not all coliform are E. coli.
What they are: Total coliform bacteria are a group of bacteria that are naturally present in the environment – in soil, on vegetation, and in the surface water. They’re also found in the intestines of humans and animals. This large group acts as an indicator.
Why they matter: The presence of total coliform in your drinking water suggests a possible pathway for harmful bacteria to enter your well. It means your water system might be vulnerable to contamination. Imagine a crack in your house foundation; it might not be letting water in yet, but it's a sign that it could. The EPA doesn't consider total coliform bacteria themselves harmful, but their presence is a red flag. It indicates that your well has a pathway for outside sources to get in, and if environmental bacteria can get in, then harmful fecal bacteria could too.
Source: (U.S. Environmental Protection Agency, Current Drinking Water Standards, 2024)
What they are: Fecal coliforms are a subgroup of total coliform bacteria. They are specifically found in the fecal matter of warm-blooded animals and humans. Escherichia coli (E. coli) is a specific species within the fecal coliform group, and it's the most common and best-known. Almost all E. coli bacteria indicate recent fecal contamination.
Why they matter: The presence of fecal coliform or E. coli in drinking water is a serious health concern. It means there has been recent contamination by human or animal waste. This waste can contain many disease-causing bacteria, viruses, and parasites. Detecting E. coli in water almost always means that there is contamination from human or animal feces, and this makes it very likely that other potentially dangerous microorganisms are also present in the water (Centers for Disease Control and Prevention, E. coli and Water, 2023).
Health Risks: Exposure to pathogenic E. coli (and other associated fecal bacteria) can cause symptoms like nausea, vomiting, diarrhea, severe abdominal cramps, fever, and dehydration. In severe cases, particularly with specific strains like E. coli O157:H7, it can lead to kidney failure (Hemolytic Uremic Syndrome) and even death, especially in young children and the elderly. You can learn more about symptoms and risks at /contaminant/e-coli.
Source: (Centers for Disease Control and Prevention, E. coli and Water, 2023)
Well water can become contaminated in various ways. Understanding these sources can help you prevent future problems.
Septic Systems: A failing, poorly maintained, or improperly sited septic system is a prime culprit. If your septic tank or drain field is too close to your well or isn't working correctly, effluent can seep into the groundwater that feeds your well. This is a common issue, especially if your well or septic system is older. Agricultural Runoff: Farms can contribute animal waste (from livestock, manure fertilizer) that washes into the ground and eventually into your well during rain or snowmelt. This is a significant concern for wells in rural areas, like those found in /state/texas agricultural regions. Wildlife and Pets: Animal waste from deer, rodents, birds, and even domestic pets can contaminate the ground surrounding your well, especially if your wellhead isn't properly sealed. Flooding and Heavy Rains: High water tables and surface water runoff during floods or heavy rainfall can overwhelm well defenses, carrying bacteria-laden soil and surface water down into the well casing or through cracks. Well Construction Issues: An old, cracked, or poorly sealed well casing allows surface water and shallow groundwater to enter. A well cap that isn't watertight or is damaged can also be an entry point. The depth of your well matters too; shallower wells are generally more susceptible to surface contamination. Poor Well Maintenance: Not regularly inspecting your well for cracks, damage, or proper sealing can lead to issues going unnoticed until contamination occurs. * New Well or Well Repairs: After a new well is drilled or significant repairs are made, the well can become contaminated during the process. It's standard practice to disinfect a well after construction or repair.
Finding out your well water has bacteria can be alarming, but it's a problem with solutions. Here's what you need to do, step-by-step.
This is the absolute first thing to do if you get a positive test result for E. coli or if you suspect contamination (e.g., strong sulfur smell, sudden unexplained illness in the household). A positive test for total coliform alone is a warning, but E. coli means immediate action.
Use Bottled Water: Switch to commercially bottled water for drinking, brushing teeth, washing fruits and vegetables, making ice, and preparing infant formula. This is not optional. Boil Water: If bottled water isn't available, bring your tap water to a rolling boil for at least one minute to kill bacteria, viruses, and parasites. Let it cool before use. This doesn't remove other contaminants like lead, but it will make it safe from biological threats /lead. * Bathing: For bathing, showering, or washing hands, the risk is generally lower, but if E. coli is present or you have open wounds, it's safer to use boiled or bottled water.
Source: (World Health Organization, Guidelines for Drinking-water Quality, 4th edition, 2011)
Sometimes, a lab error or a contaminated sample can lead to a false positive. You should immediately retest your well water to confirm the presence of bacteria, especially if the initial test was positive for total coliform but negative for E. coli.
Follow Instructions Carefully: When collecting a sample for retesting, follow the lab's instructions precisely. Improper collection is a common cause of invalid results. This means using sterile bottles, not touching the inside, and collecting from an appropriate spigot. Consider Multiple Locations: Some well owners choose to test from a few different taps in their home to see if the contamination is widespread or localized. This can provide valuable information.
If the retest confirms bacterial contamination, you absolutely need to figure out how it's getting in. This isn't always easy, and it often requires professional help.
Inspect Your Well Head: Look for cracks in the well casing, a damaged or missing well cap, or any signs of surface water pooling near the well. Make sure electrical conduits are sealed. Check Well Proximity: How close is your well to potential sources like septic systems, livestock pens, manure piles, or areas where pesticides/fertilizers are used? State regulations usually specify minimum separation distances, for example, 50-100 feet from a septic drain field. Septic System Inspection: If you have a septic system, have it inspected by a qualified professional. They can check for leaks, blockages, or overflowing drain fields. Flooding History: Has your area experienced recent flooding or heavy rains? This can often explain sudden contamination. * New Well Components/Repairs: Have you recently had any work done on your well or plumbing? Installation or repair can sometimes introduce bacteria.
Source: (National Groundwater Association, Well Owner's Guide To Water Wells, 2005)
Shock chlorination is the most common method for disinfecting a private well. It involves introducing a strong chlorine solution into the well and plumbing system to kill bacteria.
**How it works (general steps – always follow specific instructions from your well professional or local health department):
Important Considerations:
Professional Help: For complex situations, deep wells, or if you're unsure, hire a qualified well contractor. They have the equipment and experience to do it safely and effectively. To understand the contaminants common in your area first, look up your water quality by ZIP code. Concentration: The typical goal is to achieve a chlorine concentration of 50-100 parts per million (ppm) in the well water during treatment. Household bleach is usually around 5-6% sodium hypochlorite.
Source: (National Environmental Health Association, Manual of Septic Tank Practice, 2015)
Shock chlorination is a temporary fix. For lasting safety, you need to address the source of the contamination and consider ongoing treatment.
Repair or Replace Well Casing/Cap: If your well casing is cracked or the cap is damaged, get it repaired or replaced by a professional. Ensure the well cap is watertight and extends at least 12-18 inches above the ground to prevent surface water intrusion. Proper Grading: Make sure the ground around your well slopes away from it to direct surface runoff away from the wellhead. Relocate/Repair Septic System: If your septic system is the cause, it may need significant repairs, relocation, or replacement. This is a big job but sometimes necessary to protect your drinking water. Buffer Zones: Maintain adequate separation distances between your well and potential contamination sources like septic systems, animal pens, and fertilizer storage.
For persistent bacterial issues, or if you want an extra layer of protection, consider installing a continuous disinfection system.
1. Ultraviolet (UV) Light Disinfection: How it works: UV light systems use a special lamp to emit UV-C light, which scrambles the DNA of bacteria, viruses, and other microorganisms, rendering them unable to reproduce and cause illness. The water flows through a chamber where it's exposed to the UV light. Pros: Highly effective against a wide range of pathogens without adding chemicals to your water. No taste or odor changes. Low maintenance (usually just changing the bulb annually). Cons: Requires pre-filtration if your water has high turbidity (cloudiness) or iron, as particles can shield microbes from UV light. Requires electricity. Does not remove other contaminants. Source: (Water Quality Association, UV Disinfection, 2019)
2. Chemical Disinfection (Continuous Chlorination): How it works: A small amount of chlorine (or another disinfectant like hydrogen peroxide) is continuously injected into your well water system. This maintains a residual disinfectant throughout your plumbing. Pros: Very effective, provides a residual disinfectant that protects against recontamination in the pipes. Cons: Adds chemicals to your water, which can affect taste and odor. Requires additional equipment (chemical pump, contact tank). Can create disinfection byproducts (DBPs) if organic matter is present, some of which are regulated by the EPA due to potential health concerns. Recommendation: If you go this route, consider a carbon filter after chlorination to remove chlorine taste/odor and some DBPs.
Even after resolving a contamination issue and/or installing a treatment system, regular testing is paramount. The EPA recommends private well owners test their water annually for total coliform bacteria, nitrates, pH, and other contaminants of local concern. Many states and localities, like in /city/chicago suburbs, require this.
At least Annually: Test your well water at least once a year for total coliform and E. coli. After Events: Test your well after floods, heavy rains, well repairs, or if anyone in your household experiences unexplained gastrointestinal illness.
Private well owners are responsible for the safety of their drinking water. There's no municipal water utility overseeing its quality. While this means independence, it also means vigilance. Understanding what total coliform bacteria and E. coli mean, knowing the steps to take when they appear, and investing in preventative measures are crucial for protecting your family's health. Don't wait for symptoms; proactively test and maintain your well. Your health is literally in your hands.
Check your water quality by zip code to see what contaminants are common in your area. Find water filters that remove PFAS – well water owners especially benefit from multi-stage filtration. Well water can contain PFAS too – read our PFAS contamination guide for more details.
Check your water now. Enter your zip code at KnowYourExposure.com to see what contaminants have been detected in your local water supply – including PFAS, lead, and other regulated compounds.