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Recommendations for private wells inundated by flooding

Private Wells

If you live in an area that was recently or is currently flooded, your private well may be in danger of contamination from pollutants carried in floodwaters.

Bacteria, chemicals and other contaminants contained in floodwaters can enter the top of your well, seep down its casing, or migrate underground to your well via a neighbor’s flooded out well. Such contamination can make your water unsafe for drinking, cooking and preparing food.

You should suspect contamination if your well casing becomes inundated; if you notice taste, color or sediment changes in your water; or, if your well is shallow-cased and you are near areas that have been flooded. Wells in pits or basements are also susceptible to contamination.

Stop Using Your Water and Switch to a Safe Water Source

If you suspect your drinking water is contaminated, immediately stop drinking it or using it for cooking and preparing food. Switch to a known safe source such as a neighbor’s well you know is safe, a community water supply, or buy bottled water. If you can’t find a convenient source of safe water, boil your well water for one minute at a rolling boil before using it.

Have Your Well and Plumbing Disinfected

Your well and the entire plumbing system should be disinfected. This procedure is best done by a licensed well driller or pump installer with the expertise and equipment.

Here are lists of licensed well drillers and pump installers who can get the work done.

Well owners may disinfect their well and plumbing system themselves by carefully following procedures outlined in DNR’s Disinfection Procedure [PDF].

Test Your Well Water

Before using your well again, have the water tested for total coliform bacteria by a certified laboratory.

Or check for certified laboratories in the Yellow Pages or on the Internet. The State Laboratory of Hygiene also tests water and can be reached at 1-800-442-4618.

The laboratory you work through will provide you with a water sampling kit. It’s very important to make sure you follow their sampling directions. In fact, well owners frequently get false positives because they do not properly collect the sample or get it to the laboratory within the 48 hours required for an accurate test.

Watch this video demonstration showing the DNR’s recommended methods for collecting a water sample that will yield accurate results.

Read the State Laboratory of Hygiene’s recommendations on how to collect a water sample.

What to do if the water sample is positive or “present” for bacteria

Test results should be returned to you within 10 business days. If the water sample is found “present” for coliform bacteria, your water is considered unsafe. Read Bacterial Contamination of Private Wells [PDF] for more information on what to do if you receive a positive result.

Take a second sample to confirm your first unsafe result. Make sure to use the proper sampling procedure because it will help you determine if your original unsafe result was due to human error in sampling.

If the second sample results are unsafe, do not consume the water unless it is boiled at a rolling boil for at least one minute.

Replace any old, poorly-sealed well caps with a properly-fitting vermin-proof cap. If there is no such obvious source of contamination, contact your local well driller, pump installer or the nearest DNR office for assistance.

What to do if the water sample is negative or “absent” for bacteria

If the test results come back negative for bacteria, consider the water safe to drink but re-test in another month and be on the lookout for changes in the water’s taste, odor and color.

What to do to avoid future well contamination

Prevent well contamination during future flooding by having your well casing pipe raised to at least 2 feet above the regional flood elevation for your location. This height is usually the height of the flood water during the 100-year flood.

A licensed well driller or pump installer should also be hired to do this work.

Remember to test your well water at least once a year for bacterial contamination, and periodically for other contaminants, based on the land uses in your area.

Read about what contaminants to test for and when you should test your well in Tests for Drinking Water from Private Wells [PDF].

Last revised: Wednesday April 02 2014