Is my well water safe to drink after a flood?
What causes this
Floodwater contaminating the well
When floodwater reaches the wellhead, it can carry bacteria and other contaminants directly into the well. You cannot tell by looking whether the water is safe, so a flooded well must be treated as contaminated until proven otherwise.
Industrial or agricultural floodwater
If the floodwater could have picked up industrial chemicals or agricultural runoff, the well may need chemical testing in addition to the standard bacteria check.
Is it dangerous?
Assume the well is unsafe after floodwater reaches the wellhead, and do not drink the water. This is the one case where you should treat the water as dangerous by default — not because every flooded well is contaminated, but because you cannot tell without disinfecting and re-testing first.
The test that tells you
A symptom only narrows it down. To know for sure, have a state-certified lab test for:
- coliform bacteria
- E. coli
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How to fix it
Shock-chlorinate the well to disinfect it, pump the system out, and then RE-TEST for coliform bacteria before you start using the water again. If the floodwater may have carried industrial or agricultural chemicals, add the relevant chemical tests as well. Do not return to drinking the water until a follow-up test confirms it is clear.
- 1
Stop drinking the water
After floodwater reaches the wellhead, assume the well is unsafe and switch to bottled or another safe water source. You cannot tell by sight, smell, or taste whether a flooded well is contaminated.
- 2
Disinfect the well
Shock-chlorinate the well to disinfect it, following the chlorination procedure for your well's depth and volume.
- 3
Pump the system out
Pump the chlorinated water through the system and out so the disinfectant works through the well and plumbing before you sample.
- 4
Re-test before using the water
Re-test for coliform bacteria — and chemical contaminants if industrial or agricultural flooding is possible — and only return to using the water once the follow-up test confirms it is clear.
A symptom is a clue, not a diagnosis. Only a lab test of your individual well confirms what is in your water — do not assume a symptom is definitely harmless or definitely dangerous until you have tested. The county-level USGS area estimates elsewhere on this site describe a region as a whole and cannot stand in for testing your own well.
By TapWaterData Editorial
Frequently asked questions
Is well water safe to drink after a flood?
No — assume it is unsafe. When floodwater reaches the wellhead it can carry bacteria and other contaminants into the well, and you cannot tell by sight, smell, or taste whether it is safe. Treat the water as contaminated until you have disinfected the well and a follow-up test confirms it is clear.
How do I disinfect a well after flooding?
Shock-chlorinate the well to disinfect it, pump the system out so the chlorinated water clears, and then re-test for coliform bacteria before using the water again. If the floodwater may have carried industrial or agricultural chemicals, add the relevant chemical tests too.
How long after a flood should I wait to use my well water?
Wait until you have disinfected the well, pumped it out, and received a follow-up test confirming the coliform bacteria are clear. Time alone does not make a flooded well safe — only disinfection plus a passing re-test does.
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