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Well Water Contamination from Septic Systems

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Many homeowners who use a septic system to provide wastewater treatment for their home often get their drinking water from a private well. If the septic system is malfunctioning or happens to be located too close to a drinking water well, contaminants from the wastewater can end up in drinking water. Learn how to locate, operate, and maintain your septic system to protect nearby wells and preserve the groundwater. Your septic system could contaminate your drinking water well or a nearby well under certain conditions, so it is important to regularly test the drinking water from your well (once a year is recommended) and take corrective action as needed.

Water from your toilets, showers, and other appliances contains harmful bacteria, viruses, and nutrients that could make you sick if it were to enter your well without being properly treated first. Maintenance issues like a full or cracked septic tank or a plugged drainfield can cause untreated wastewater to enter the surface water or groundwater. 

According to U.S. EPA: "Filtering wastewater through the soil removes most bacteria and viruses (also known as pathogens) and some nutrients. While soil can treat many contaminants, it cannot remove all of them (e.g., medicines, some cleaning products, other potentially harmful chemicals). If untreated wastewater surfaces in the yard, wastewater may contaminate your drinking water through an unsecured well cap or cracks in the well casing. It’s important to avoid flushing medication and chemicals into your wastewater since it could contaminate your drinking water."

The contamination risk to your well is lower the farther apart the well and septic system are located, the deeper the well is placed (and if it is in bedrock or below a defined layer of silt or clay,) or when your septic system is pumped and serviced on a regular basis.

The contamination risk to your well is higher if the well is at a shallow depth and in permeable soil, if the groundwater flows from the septic system towards the well, if there are many homes on septic systems near the well, or if there is poor construction or maintenance of the well and/or septic system.

Of course, there are a number of factors that can contribute to well contamination, from human mistakes and interference to natural groundwater chemistry. This video from our sister site,, discusses the basic circumstances that can lead to contaminated well water, and the kinds of naturally occurring contaminants that can be found in private wells.