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Understanding Well Water Risks After a Flood

Did you know that a flood could contaminate the drinking water in your well? Find out what the risks are and how Missouri homeowners can care for a well after a flood.

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After a flood, there is one part of cleanup that can be dangerous to overlook—well water. Flooding can directly impact the quality of private wells and drinking water, and as a homeowner in Missouri, it’s critical to understand how your health and safety could be affected. 

Let’s break down the well water risks after a flood and what you can do to stay safe. 


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What Contaminants Are in Floodwaters?

Floodwaters will carry the contaminants of whatever it touches. That could be car fluids, industrial waste, sewage, chemicals, pesticides, and more. Floodwaters also carry bacteria such as E.coli and coliform.  

There’s a good reason the CDC recommends that anyone who touches floodwaters wash their skin with soap and clean water as soon as possible. Contact with floodwater can cause rashes, infections of open wounds, vomiting, and other gastrointestinal illnesses. 

How Can Flooding Contaminate Your Well?

If flooding reaches the private well in your yard, the well water will likely become contaminated. Whatever contaminants are in the floodwater will spread to your drinking water. This means that the same health risks of the floodwaters in the streets apply to the water coming out of your faucet. 

As a private well owner, you are independently responsible for its quality and safety. This responsibility is important at all times of the year, but the increased risk of contamination after flooding makes it an important concern.

Learn more about well water contamination with the EPA’s explanation of well water contamination sources and the CDC’s explanation about how different well water contaminants can affect your health. 

How Close Does Flooding Have to Be For It to Contaminate Your Drinking Water?

Because of how water moves above and below the surface of the soil, floodwaters don’t have to directly contact your well head to contaminate your well water. 

A well draws its water from deep in the ground. Simultaneously, flooding can spread contaminants to the groundwater below the surface of the soil. A well could still be contaminated from a nearby flood if the well reaches the groundwater tables below. 

Has Flooding Affected Missouri’s Well Water?

Yes, flooding has affected well water in many areas of Missouri, including Kansas City and St. Louis

One of the biggest analyses of Missouri’s well water contamination was after the Midwestern floods of 2019. Of the approximately 400,000 private wells in Missouri, the National Ground Water Association estimated that 96,314 wells were potentially affected.

That means 24 percent of wells in Missouri were potentially impacted by flood contamination.

The biggest risks were E.coli, coliform, and other pathogens because human and animal fecal matter contaminated floodwater after exposure to farms, agricultural facilities, septic systems, and sewage treatment plants.

8 Steps to Protect Your Well Water After a Flood

Following these eight steps can help you ensure your well is safe after a flood. 

1. Test your well. 

There is no way to know what’s in your water until you test the well. Some local health departments provide free testing for private wells. The EPA is another great resource for well water testing. You can call the Safe Drinking Water Hotline at 1-800-426-4791 or visit their resource for water quality of private wells. The Missouri Department of Natural Resources also keeps a directory of water testing labs that have been certified by Missouri.

2. Run water until clear.

Your health department or water testing lab may offer guidance about the steps to take before and after your well water is tested. The first step to disinfecting your well is to use an outside spigot and run the water until it becomes clear. This will flush your lines of any sediment, cloudiness, or particulate.

3. Shock well with bleach. 

The design of each well head is slightly different, and disinfecting some wells may require that you remove an air vent, plug, or cover. Use the manufacturer’s guidelines and pour the recommended amount of non-scented bleach into the well casing.

Then cycle the water to mix the bleach. To do this, use an outdoor hose, and add water into the well casing until you smell chlorine coming from the hose. 

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

You want to circulate the bleach through your home’s entire plumbing system to kill any bacteria that could be lurking inside your pipes. On each faucet indoors and outdoors, run the cold water until you start to smell the bleach coming out of the faucet, and then shut all faucets off.

Wait six to 24 hours before turning faucets back on, and do not use the water for any purpose during this time.

When ready, run the water from an outdoor hose until you no longer smell the bleach. Remember that this water has high concentrations of bleach so direct water to a safe area that will not contaminate plants, streams, or septic tanks.

5. Re-test water.

About seven to 10 days after disinfection, have your well water retested. Rather than testing your water immediately, the delayed testing gives your system an incubation period. If small amounts of bacteria were still in your system after the bleach treatment, waiting a week gives them a chance to re-populate to detectable levels. Testing too early could give you a false reading that your drinking water is safe.

Remember to take a long-range view to well safety and repeatedly test your well in the months following a flood. Contamination from nearby sites could leech into the groundwater, and these problems may not impact your well until long after the floodwaters have receded.

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

Never use a septic system after a flood. There are many potential health and safety risks, and always follow the recommendations of a plumber or safety inspector. For example, your septic system could fail if the soil in the leach field is too saturated. The unfortunate result could be sewage backing up into your basement.

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

Recovering from a flood can be a long process, and drinking water issues can cause serious illnesses. Drink bottled water until you know your water is safe.

8. Get a professional foundation inspection to identify hidden flood damage to your home.

A flood could damage your home in unexpected ways, and acting quickly can help you avoid the worst outcomes. The longer the flooding persists, your structure could become weaker, walls could start to bow or crack, and black mold could start to grow.

Get a free inspection from Foundation Recovery Systems to find out if your home has flood damage, and use this flood prevention checklist to learn how you can help protect your home from flood damage.

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