Maintenance & Seasonal Care

What to Do After Flooding Near Your Well

Floodwater can introduce bacteria, chemicals, agricultural runoff, and sewage into your well. Do not assume your water is safe to drink after flooding in the area—even if it looks and tastes normal. Follow this protocol.

🚨 Immediate Action Required

Do not drink, cook with, or brush teeth with water from a well that was submerged or surrounded by floodwater until you have completed shock chlorination AND received a negative (clean) bacteria re-test result. Use bottled water or water from a tested safe source in the interim.

Why Flooding Contaminates Wells

A properly constructed well is sealed to prevent surface water from entering the casing. But flooding creates conditions that overwhelm those seals:

  • Floodwater surcharges the ground around the wellhead and can infiltrate through any gap in the cap, casing, or grout seal
  • Older wells with damaged or deteriorated grout seals are highly vulnerable
  • The hydraulic pressure of standing water can force contaminated water through minor casing defects that were never problematic before
  • Submersed wellheads (actual inundation) always require sanitization regardless of well construction quality
  • Groundwater itself can be temporarily contaminated after major floods as surface water recharges the aquifer

Floodwater contains bacteria (E. coli, coliform), agricultural chemicals, fuel, sewage, and sediment. Any of these entering your well represents a serious health risk.

Post-Flood Response Protocol

  1. Do not use the water for drinking or cooking

    Implement a boil water advisory for your household immediately. Use bottled water for drinking, cooking, brushing teeth, and making infant formula. Bathing in potentially contaminated water is lower risk but showering should be brief and care taken not to swallow water.

  2. Wait until floodwater fully recedes before inspecting or treating

    There is no point in sanitizing while the well is still partially submerged. Wait until water levels have fully receded from the area before proceeding. This may be 24–72 hours after the flood event.

  3. Inspect the wellhead

    Once flood water recedes, inspect the wellhead for: displaced or damaged cap, debris inside the casing, sediment inside the casing, structural damage to the casing above or at ground level. Photograph all damage. If the casing has visible structural damage (cracks, significant corrosion, separation), call a licensed well contractor before attempting sanitization.

  4. Remove debris from the casing

    If sediment or debris has entered the casing, it must be physically removed before chlorination. Pumping the well to waste (directing pump output to drainage away from the property) can help flush debris, but some situations require a contractor to bail or swab the well.

  5. Perform shock chlorination

    This is the standard sanitization procedure after flood contamination. See our complete shock chlorination guide → for the exact procedure, chlorine quantities, and timing. After shock chlorination, the well must be flushed until no chlorine odor remains at the taps.

  6. Wait 7–14 days, then re-test

    Do not test immediately after chlorination — residual chlorine will suppress bacteria in the sample and produce a false negative. Wait at least 7 days (preferably 10–14) after flushing before collecting a re-test sample. Use a state-certified lab. Find a lab →

  7. Interpret re-test results

    If re-test is negative (clean): the well has been successfully sanitized. Resume use cautiously and re-test again in 30 days to confirm.
    If re-test is still positive: shock chlorination alone has not resolved the issue. Call a licensed well contractor — structural damage likely requires professional repair before sanitization will hold.

  8. Consider a broader test panel after flooding

    In addition to bacteria testing, a post-flood test should include nitrates and any agricultural chemicals or industrial contaminants known to be in your area. If flooding was associated with a chemical spill or agricultural runoff event, contact your state health department for specific testing recommendations.

If FEMA or Federal Assistance Is Involved

If your property is in a federally declared disaster area, FEMA and your state health department may offer:

  • Free or subsidized water testing
  • Technical assistance for well sanitization
  • Contractor referrals for well repairs
  • Assistance payments for well remediation in some disaster declarations

Contact your state’s emergency management agency and local health department for available resources. Keep all receipts for well testing and remediation costs — these are potentially reimbursable under FEMA Individual Assistance programs.

The flood didn’t directly reach my wellhead — do I still need to test?▼
If the wellhead was not inundated and flooding did not reach within the wellhead’s immediate area, your risk is lower but not zero. Major flooding events can temporarily contaminate shallow aquifers as surface water infiltrates the water table. If you are on a shallow well (less than 50 feet deep) or a dug well, testing is advisable after any significant regional flooding event even if your wellhead was not directly affected.
The flood was 3 weeks ago and we’ve been drinking the water with no problems — do I still need to test?▼
Yes. Many water-borne pathogens cause illness on a delay, and some contaminants (nitrates, arsenic, chemical compounds) cause long-term health effects with no immediate symptoms. The absence of immediate illness does not confirm water safety. Test now — it’s not too late to establish whether your well was affected.
Disclaimer This guide reflects general best practices. For health emergencies or if vulnerable household members have consumed potentially contaminated water, contact your local health department or medical provider immediately.