Restoring and Sampling Private Wells After a Flood

After flooding, water from private wells may not be safe to drink. Private well owners should take steps to restore their private water supply. When a water supply well has been flooded, the water in the well may be contaminated with germs (waterborne pathogens) that can cause serious illness in humans and pets. If you believe that your well has been contaminated, stop using your well water for drinking and cooking purposes. Check with your local health department about other acceptable sources of water.

If you believe your well may be contaminated by gasoline, heating oil or other chemicals, do not use your well and immediately contact your local health department or the Department of Environmental Conservation Spill Hotline at 1-800-457-7362.

This fact sheet provides guidance on how to address possible pathogen contamination.

How to Safely Get a Flooded Well Back into Service

There are four action steps needed to safely get a flooded well back into service:

diagram of typical house and well set up
  • Assessment
  • Repair & Flushing
  • Disinfection
  • Sampling

Assessment: What to Look For

A flood will leave warning signs that a water well may be unsafe. Floodwater carries large pieces of debris that can dislodge parts of the well and distort or crack the well casing. Floodwater may also deposit mud or sediment in the well. If you see any of these conditions you should have a professional repair the system.

Below are things that a well owner can look for; any one of these signs may indicate that a well is contaminated and the water may be unsafe. If you suspect the well has been affected by floodwater, stop using it until it is checked.

Most private wells have the well pump located inside the well casing and submerged, so well owners will probably not be able to inspect the pump. If the pump or well casing needs repair, contact a qualified professional, registered well driller, or pump contractor to evaluate and service it. Do not turn on your well pump until the well has been assessed and repaired as needed. Contact your local health department for help in locating registered well contractors. The Department of Environmental Conservation has a list of registered water well contractors.

6 Steps to Assess Your Well
Step What To Look For When to Call a Professional
2. Check whether the well was flooded Check your well for flood water or signs of flooding. If you did not see the area during the flood, debris and mud in the area and water or mud stains on the well may indicate that the well was flooded If you don't have safe access to the well, call a professional to check for damage.
3. See if the ground surface around the well is broken or unstable Check for erosion around the well that may lead to unsafe conditions or a pathway for surface water and contaminants to get in. A professional may be needed to re-grade land around the well or repair/replace the well or casing.
4. Inspect electrical components and wires Look for exposed or damaged wiring or electrical components. Visually check whether there is water in any electrical components. Do not touch visible electrical wires; they may be dangerous due to electric shock. If electrical connections or controls located outside the well casing remain submerged, do not turn on the pump because it may cause electric shock or damage to the system. A qualified electrician or well professional should be contacted to evaluate the electrical components if any water or damage is seen, or if it is suspected that any part of the electrical system has been submerged.
5. Check the well casing A bent or cracked well casing may allow surface water, sediment and debris to enter the well and will increase the risk of contamination. Professional replacement of the well casing may be needed to restore the well.
6. Check the well cap and seal See if the cap and seal are securely fastened to the well casing. A loose well cap may allow sediment and debris to contaminate the well. If sediment and debris have entered the well, call a professional before restarting the well.

Repair & Flushing: How to Clean It

Take the following steps before using the well again. Be sure the electricity is off until you complete your check of the well as shown above. Never step in water around a well, unless you are sure the power is off.

Wait until the well has been restored by proper flushing and disinfection before you drink or wash with well water.

4 Steps to Flush your Well
Step Instructions
1. Clean Remove any visible mud, sediment, and other debris from the well casing, cap, and other accessible components. If there is excessive mud or sediment in the well, get professional help to remove the pump before cleaning or repairing.
2. Re-grade If the ground is sloped down toward the well, re-grade soil so surface water flows away from the well casing. Surface water may contain contaminants that can get into the well if water flows down along the well casing.
3. Start pump After the pump has been inspected and repaired, or replaced, turn it on. If it does not start or pump water, get assistance from a registered well driller or pump contractor.
4. Flush Pump the water until it runs clear to get rid of any floodwater in the well. Use a hose connected to an outside faucet, so the flushed water flows to a nearby drainageway rather than into your septic system or public sewer (after flooding, both septic systems and public sewers may be overwhelmed and unable to hold more wastewater). Depending on the size and depth of the well and extent of contamination, pumping times will vary…it may take 30 minutes, or it could take several hours or days until the water runs clear.

Disinfection: How to Kill the Germs

ELECTRICAL SAFETY -- EXTREME CAUTION is advised when disinfecting a well.

Electricity near water can be dangerous. Before you do anything to the well:

  • Turn off the pump circuit breaker.
  • Examine for chafed wire insulation or missing wire nuts and repair, as necessary.
  • Wear rubber-soled shoes or boots, preferably waterproof.

Disinfect (sanitize) your water to kill germs before using the water for any household purposes. Changes in the water's appearance, taste, or odor may indicate contamination. Even if your well is working, you should use other sources of water for drinking, food preparation, and brushing teeth until your well test results show the water is safe to drink. Check with local health department personnel about other acceptable sources of water.

Before using well water, a concentrated bleach solution needs to be circulated through the well and house plumbing to assure proper disinfection. Below is a step-by-step method to sanitize a well before restoring it to full use. If you have a "point well", or if the well pump is a jet pump, it is recommended that you hire a water well contractor to disinfect your well.

12 Steps to Disinfect your Well
Step Instructions
1 Attach a hose to the outdoor faucet that is closest to the well or pressure tank. The hose needs to be long enough to reach the well. Run water through the hose until it is clear.
2 Mix 2 quarts of regular, unscented household bleach in 10 gallons of water in a large bucket (or 1 quart of bleach in 5 gallons of water and then repeat) in the area of the well casing. Do not use splashless, scented, or gel variety bleach.
3 Turn off the electric power to the well pump (switch is probably located at the circuit breaker box or near the pressure tank). Carefully remove the well cap (and well seal, if there is one). Set aside.
4 Turn back on the electric power to the well pump. Place the other end of the hose into the casing. Turn on the faucet with hose.
5 While the water is running through the hose, carefully pour all 10 gallons of the water and bleach solution from the bucket down the open well casing. At the same time, continue to run the water through the hose placed inside the well casing.
6 Run the water at each indoor and outdoor faucet until a chlorine odor is present, and then shut off each faucet (except the faucet where hose is attached).
7 Continue running water through the hose and down inside the well casing to recirculate the chlorine solution. Use the hose to also wash down the inside of the well casing.
8 After one hour of recirculating the water, remove the hose from the well. Fill a bucket with 10 gallons of water. Shut off the faucet the hose is connected to and make sure all the other faucets are still shut off to assure the pump is stopped. Remove the hose from the well.
9 Mix 2 more quarts of bleach in 10 gallons of water. Use about half a gallon of the mixture to rinse and disinfect the well cap (and seal, if there is one). Turn off the electric power to the well pump. Pour the remaining mixture into the well. Replace the well cap (and seal).
10 Allow the well to stand idle for at least 8 hours, and preferably, 12 to 24 hours. Avoid using the water during this time. The electric power to the pump still needs to be off.
11 After the well has been idle for 8 to 24 hours, turn the electric power to the well back on.
12 Purge the well and plumbing of the chlorinated water:
  1. Connect a hose to an outside faucet and place the other end of the hose away from grass and shrubbery.
  2. Open the faucet and run the water until the chlorine odor disappears.
  3. Open all the other indoor and outdoor faucets until the chlorine odor disappears.
Now that you have disinfected the well and house plumbing, the water needs to be tested to confirm it is free from contamination.

Sampling: How to Sample and Test Your Well

After the well has been properly disinfected and the chlorine has been flushed out of the water system (the water should not smell of chlorine), test the water to confirm that it is free from contamination. If chlorine odors persist, you may have to repeat flushing or wait several days before testing to be sure that all the chlorine has been flushed from the water system. Until testing shows that the water is free of contamination you should use bottled water or check with local health department personnel about other acceptable sources of water.

Pre-Sampling Checklist

Before sampling the well water, be sure the following have been done:

  • The area around the well has drained of floodwaters and has been cleaned up.
  • The well is in good condition, operable, and any needed repairs have been completed.
  • The well has been flushed of any floodwater that may have entered it, and the attached plumbing has been properly disinfected.
  • The well has been disinfected and the pipes have been flushed to remove chlorinated water.

Proper Sampling Techniques

Proper sampling techniques are very important for true and accurate results. Follow these steps when sampling your well:

9 Steps to Sample Your Well
Step Instructions
1 Obtain a sterile "BacT" bottle from a laboratory certified by New York State for drinking water analysis. You may also contact the health office that serves your county.
2 Do not open the bottle until you are ready to fill it, and close it immediately once it is filled with sample water. Do not rinse the contents from the bottle. Do not touch the inside of the bottle or bottle cap with your fingers (if you do, STOP and get another bottle).
3 From the kitchen cold water tap, remove the anti-splash screen from the faucet.
4 Disinfect the faucet tip by dipping it in a capful of bleach, or by "flaming" the faucet tip with a lighter or match for 10 seconds (be sure to remove rubber faucet seals first).
5 Let the cold water run for 4-5 minutes.
6 Fill the sterile bottle to the 100ml line and cap it tightly. REMEMBER…do not touch the inside of the bottle or lid.
7 Fill out the sample label and form provided by the lab. Remember to add contact and address information.
8 Put the filled bottle in your refrigerator.
9 Return the bottle to your chosen laboratory. Make sure to keep the sample chilled on the way to the laboratory.

Next Steps to Protect Your Well

There are some improvements you can make to protect your well from future damage.

Retest Your Well You should consider retesting the well water after several weeks. If flooding and groundwater contamination is extensive, your well may be at risk of recontamination for some time.
Drill a New Well If frequent flooding of your well occurs, consider drilling a new well where it is not subject to flooding. Make sure your well is constructed in such a manner that seasonal floodwater cannot enter the well. Contact a registered well driller for advice.
Grade Around the Well The ground surface immediately surrounding a well casing and, if possible, the property in general, should be graded to direct surface water away from the well. If erosion around the well has been a problem, consider protecting the area with plants or shrubs, or take other erosion control measures.
Extend the Well Casing Casing can be extended to a height above the expected or experienced level of the floodwater to keep floodwaters out. In flood-prone areas, it is recommended that the well casing be extended at least 1–2 feet above the highest recorded flood level. A registered well driller should perform this work.
Upgrade the Well Cap Install a well cap that will prevent water, insects, and rodents from getting in. A registered well driller should perform this work.

If you have questions, please contact your local health department for more information.

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