How soon should I test my well after a flood?

Test as soon as you can safely access the well after the flood recedes. Don't wait weeks. Many state labs offer expedited results in 24 to 48 hours for post-disaster samples. Until you have clean results in hand, treat the water as contaminated and use bottled water for all drinking, cooking, and tooth-brushing.

Can I use well water to wash dishes after a flood?

Not until testing confirms it's safe. Bacteria from floodwater can survive on dishes and utensils even after washing. If you have no other option, use the hottest water available and a sanitizing dish soap. But the safest move is to use bottled water for anything that touches food or your mouth until results come back clear.

Does boiling water make it safe to drink after a flood?

Boiling kills bacteria, including E. coli and coliform. But it does not remove nitrates, heavy metals, or chemical contaminants. If there's any chance of agricultural runoff or a chemical spill near your well, boiling alone isn't enough. Use bottled water in those cases. Boiling is an acceptable backup only when bacterial contamination is your sole concern.

How do I shock chlorinate my well after flooding?

The EPA's shock chlorination guide at epa.gov/privatewells walks through the process step by step. The basic method involves adding a diluted bleach solution to the well, running water through every tap until you smell chlorine, then waiting 24 hours before flushing the system. After flushing, wait several more days before retesting. Retest before resuming normal use.

My well tested positive for bacteria after a flood. What do I do now?

Shock chlorinate the well immediately. After the 24-hour contact period, flush the system and retest. If the well tests positive a second time, the casing or structure is likely damaged. Contact a licensed well contractor. There may be a physical entry point that chlorination alone won't fix. A clean test result after one chlorination cycle is common, but don't skip the retest.

How to Test Your Well After a Flood or Hurricane

Disclaimer: This page provides general information for private well owners. It is not a substitute for guidance from your state health department or a licensed well contractor.

After Hurricane Helene moved through the Southeast in 2024, testing found E. coli or coliform contamination in roughly 40% of private wells in the storm’s path. That number surprises people. It shouldn’t. Flooding is one of the most common ways a private well becomes unsafe overnight, and most owners don’t realize how quickly it happens.

If floodwater reached your well, your property, or your county, read this before you turn on a tap.

Do not drink well water after flooding until you have tested it and confirmed it is safe. Use bottled water or boil water for all drinking, cooking, and tooth-brushing until test results come back clear.

How Flooding Gets Into Your Well

Floodwater carries everything the land collected on its way to your property: soil bacteria, agricultural runoff, manure, fuel, and sewage overflow. When that water reaches your well, contamination can enter in more than one way.

The most direct path is surface water entering the well casing. Shallow wells (typically less than 50 feet deep) are much more vulnerable than deep wells because they draw water from near the surface. If the floodwater level exceeds the top of your casing, you almost certainly have contamination.

Pressure changes in the aquifer are less obvious but still real. Heavy flooding can alter groundwater pressure enough to pull surface contamination downward through soil that normally acts as a filter.

Physical damage is the third path. Floodwater can knock a well cap loose, crack older PVC casing, or disturb the grout seal around the casing. Any breach creates a permanent contamination pathway that chlorination alone won’t fix.

Finally, flooding stirs up sediment. Turbid, discolored, or foul-smelling water after a flood isn’t just an aesthetic problem. Sediment harbors bacteria and clogs filtration systems. If your water runs brown or cloudy, something got in.

What to Test For

Not all flood scenarios are the same. What you test for depends on your location and what the floodwater carried.

Bacteria first. Total coliform and E. coli testing is the priority for any flood event. These are the most common post-flood contaminants, they’re the most dangerous in the short term, and every certified lab can run them cheaply. A basic bacteria test costs $15 to $40 at most state labs.

For more on what bacterial contamination in well water means, see our guide to bacteria in well water.

Nitrates if you’re near farmland. Agricultural runoff during flooding carries fertilizers. Elevated nitrates are especially dangerous for infants under six months old. They cause methemoglobinemia, sometimes called blue baby syndrome. If your well is in or near a farming area, add a nitrate panel to your order. Learn more about nitrates in drinking water.

Turbidity. Many state labs include this in their standard post-flood panel. Cloudy water suggests sediment infiltration and can point to a compromised casing.

pH. This one shifts during contamination events and gives a quick read on whether something changed in your water chemistry.

Chemical panels for specific events. If a fuel tanker overturned in floodwater near you, or if there’s an industrial facility upstream, add a VOC panel. If a nearby train or truck carrying agricultural chemicals was affected, ask your state health department what they recommend testing for. General bacteria panels won’t catch chemical contamination.

Immediate Steps While You Wait for Results

The window between a flood event and your test results can be several days. Here’s what to do in that window.

Use bottled water for all drinking and cooking. Don’t make exceptions for coffee or tea. Boiling water brought to a full rolling boil kills bacteria, but if you have any reason to suspect chemical contamination, only bottled water is safe. Boiling concentrates nitrates. It doesn’t remove them.

Don’t use well water to prepare infant formula, brush teeth, or make ice. These are easy to forget.

If you’re in an emergency situation with no bottled water and you’re confident the only risk is bacterial, bring water to a full rolling boil for one minute (three minutes above 6,500 feet). That’s your backup. Not your first choice.

When and Where to Test

Test as soon as you have safe access to the well after floodwater recedes. The sooner you know, the sooner you can act.

Your state health department maintains a list of certified labs. Most state labs fast-track post-disaster samples and can return results in 24 to 48 hours. After a federally declared disaster, FEMA and state emergency agencies sometimes coordinate free testing for affected households. Check with your county emergency management office.

Our best mail-in water tests guide covers certified lab options if your state lab has a backlog. Make sure any mail-in lab is certified for drinking water testing in your state.

You can also check the full well water testing guide for how to collect a sample correctly. A contaminated sample bottle or improper collection technique can produce a false negative.

If the Test Comes Back Positive

A positive result for bacteria is common after flooding. It’s fixable, but it takes time.

Shock chlorinate the well immediately. The EPA has a free step-by-step guide at epa.gov/privatewells. The process involves adding a diluted household bleach solution to the well casing, flushing every tap until you smell chlorine, and letting the system sit for 24 hours. After that contact period, flush again and wait several days before retesting.

Don’t resume normal use until you have a clean retest. One positive result followed by one clean result is a common pattern after shock chlorination, but the retest is not optional.

If the well tests positive a second time after proper shock chlorination, the casing or physical structure is likely damaged. A licensed well contractor needs to inspect and repair it. Chlorination can’t fix a cracked casing or a loose cap.

Get a Structural Inspection Too

A clean bacteria test result doesn’t rule out physical damage. If floodwater reached or exceeded the top of your well casing, a licensed contractor should inspect the casing, cap, and grout seal before you return to normal use.

This matters because a compromised casing means contamination can re-enter with the next rain event. A one-time clean test result after flooding doesn’t mean your well is structurally sound going forward.

The Bottom Line

Any time floodwater reaches your well or your county issues a flood warning, treat the water as potentially contaminated until testing proves otherwise. A bacteria and nitrate panel costs $15 to $40. Use bottled water until results come back. If results are positive, shock chlorinate, retest, and get an inspection if the problem persists.

A well that looks fine after a flood can still be carrying E. coli. You can’t tell by looking at it.

Disclaimer: WaterAnswer.com provides general information for private well owners. Nothing on this page is a substitute for guidance from your state health department, a licensed well contractor, or other qualified professional.