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Minnesota Well Water Risks After a Flood

After a flood, your well water could be contaminated with bacteria, sewage, or something else. Learn why your water is at risk and how to protect your health and home.

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It can be easy to assume that after floodwaters subside, your water problems are over. But for Minnesota residents who use well water, there is another problem to deal with—drinking water contamination. 

Learn how flooding can lead to unsafe drinking water, ways to manage well water risks after a flood, and steps you can take to disinfect your well. 


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What Contaminants Could Be In Floodwaters?

During a flood, water can overtake streets, homes, cars, farms, industrial areas, and much more. The floodwaters will pick up contaminants from whatever it touches. 

Floods overtaking septic systems can leach sewage into the floodwater. Similarly, floodwaters could be contaminated with car fluids, pesticides, chemics, industrial waste, and more. In addition to the toxic and dangerous substances, floodwaters will also contain several types of bacteria. E.coli and coliform contamination is likely based on how often sewage contaminates floodwaters. 

Because of the dangerous contamination, contact with floodwaters can cause skin rashes, wound infections, vomiting, and gastrointestinal illnesses. The CDC recommends that anyone who touches floodwaters should wash their skin as soon as possible with soap and clean water. 

How Close Do You Have to Be to Flooding For It to Affect Your Well Water?

Because water easily mixes with itself, your water will likely be contaminated if flooding reaches the well on our property. This means the water coming out of your faucet could have the same risks as the floodwaters in the streets, fields, and parking lots. 

However, the floodwaters don’t even need to come in direct contact with your well for contamination to occur. Keep in mind that groundwater is also moving below the surface of the soil. As floodwater seeps into the soil, the contaminants could leach into the groundwater. If your well reaches down into this contaminated groundwater, your drinking water may not be safe. 

EPA’s guide to sources of well water contamination can help you decipher what could be in your well water based on local sources of contamination or observations. 

How Has Flooding Affected Wells in Minnesota?

Private wells are an important water supply in Minnesota, and about one in five Minnesotans relies on private well water.

During the Midwestern flooding of 2019, the National Ground Water Association (NGWA) estimated that the impact on well water was significant. Their geographic analysis reported that 254,922 Minnesota wells were potentially contaminated. If we assume that an average of two people per well, that would be a half-million Minnesota residents without clean drinking water.

This flooding created a significant water quality risk throughout the state. However, it doesn’t take a major event for well water to become contaminated. Minnesota state health officials estimate that at any given time, about one-quarter of the state’s private wells are contaminated with coliform bacteria because of groundwater seepage. 

8 Steps to Protect Your Well Water After a Flood

As an owner of a private well, you’re solely responsible for the safety and quality of the water. If you have concerns about well water contamination after a flood, follow these eight steps. 

1. Test your well. 

Testing your well is the only way to know what’s in your water and if it’s safe to use. The Minnesota Department of Health offers helpful resources including lists of state-accredited labs where you can get your water tested.

2. Run water until clear.

When you’re ready to disinfect your well, begin by running the water in an outside faucet until the water is clear. This will flush out any sediment. 

3. Shock the well with bleach. 

Follow the recommended procedures for disinfecting your well, including removing the well cover and pouring the specified amount of bleach into the well casing. Mix the bleach into the well by cycling water through your system. Using an outdoor hose, add water into the well until you smell chlorine coming out of the hose. 

4. Populate the lines, wait, and flush system.

To distribute the water and bleach solution through your home’s pipes, run the cold water on each faucet in your home until you smell bleach, and then shut off the faucet. Wait six to 24 hours without using the water to give the bleach solution time to kill any bacteria. Then use an outdoor hose to run the water until you no longer smell bleach coming out of the hose. 

5. Re-test water.

To get a true reading as to whether you’ve killed all of the bacteria in your pipes, wait seven to 10 days after disinfection before retesting your water. Testing too soon can give you a false negative result because any remaining bacteria will need time to repopulate to detectable levels. Because groundwater contamination after a flood can show up months after the event, take a long-range view to well safety and retest every few months to confirm safety. 

6. Don’t use septic systems immediately after a flood.

After a flood, the saturated soil could cause your septic system to fail. Sewage could back up into your home, bubble up out of the ground, or contaminate your well. Consult a plumber about when it’s safe to start using your septic system. 

7. Drink bottled water until you are certain water is free of contaminants.

Contaminated well water can have serious health consequences. It’s important to wait until your water is safe before you start drinking it because you could be dealing with other issues after a flood, including foundation repairs, installing a sump pump, or improving drainage

8. Get a professional foundation inspection to identify hidden damage.

Flooding can affect many parts of your home that you don’t see, and water is one of the leading causes of foundation damage. Floods can weaken the structure of your home, cause mold to grow, and disrupt underlying soil, which can destabilize the foundation. 

Whether you need to repair flood damage with foundation repair or you want to help prevent flood damage with basement waterproofing, sign up for a free inspection from Innovative Basement Authority.

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