Flooding is one of the most common causes of private well contamination. Even a well that has tested clean for years can become contaminated after a flood event. Here is what to do — and in what order.
If your well was submerged in or near floodwater, do not drink, cook with, or brush teeth with the well water until it has been tested and treated. Floodwater carries bacteria, sewage, agricultural runoff, chemicals, and sediment — all of which can contaminate a well.
If the well casing contains floodwater or heavily sediment-laden water, pump it out using a submersible pump until clear water appears. Do not use your drinking water pump for this — rent or borrow a trash pump. Dispose of pumped water away from the well and away from any water source.
After the well is pumped clear, shock chlorinate with household bleach. For a flooded well, use 2–4 quarts of bleach rather than the standard 1–2 quarts. Follow the full shock chlorination process: circulate chlorinated water through all faucets, let sit 12–24 hours, flush completely until no chlorine smell remains.
Wait 2 weeks after shock chlorination, then test with a certified laboratory for:
If bacteria are still present, repeat shock chlorination and retest. If bacteria persist after two rounds of shock chlorination, have a well contractor inspect the casing for structural damage.
A flooded well may pass initial testing but develop contamination weeks later as water table conditions change. Test monthly for the first 3 months after a major flood event, then resume annual testing.
Do not let children or pets drink well water after flooding until testing confirms safety. Use bottled water for all drinking, cooking, and infant formula preparation until the well tests clean.
No. Even if the water looks clear, do not drink, cook with, or brush teeth with well water after a flood until it has been tested and treated. Floodwater carries bacteria, sewage, agricultural runoff, chemicals, and sediment that can contaminate a well without visible signs.
Use 2-4 quarts of bleach for a flooded well, roughly double the standard 1-2 quarts used for routine shock chlorination, since floodwater contamination tends to be more severe.
First inspect the well cap for cracks or damage, check for mud or debris around and inside the casing, and check the pump and pressure system for damage. Don't attempt to pump a well with visible debris inside, since sediment can damage the pump.
Pump it out using a submersible trash pump (not your drinking water pump) until clear water appears, then dispose of the pumped water away from the well and any other water source.
Wait 2 weeks after shock chlorination before testing. Test with a certified lab for total coliform bacteria and E. coli (both required), plus nitrates if you're in an agricultural area and any other locally relevant contaminants.
Use our free decoder to understand what your well water test results mean.
Use the Free Decoder →