After a flood: your septic system and well

Floodwater is one of the biggest threats to a private well and a septic system at the same time. It can carry sewage, fuel, and farm runoff into the well. It can also saturate the drainfield so the septic system can't drain. Here's the order to deal with things once the water goes down.

1. Assume the well water is unsafe

If floodwater covered or came near the wellhead, don't drink the water or use it for cooking, brushing teeth, or making formula until it's been tested. Use bottled water. If you have to disinfect water, EPA's emergency guidance says to bring it to a rolling boil for at least one minute (three minutes above 5,000 feet). If boiling isn't possible, add unscented bleach, 8 drops of 6% bleach or 6 drops of 8.25% bleach per gallon, doubling it if the water is cloudy or very cold. Stir, and let it stand 30 minutes. Boiling and bleach don't remove fuel or chemical contamination.

2. Stay safe around the well

Floodwater can damage the electrical parts of the pump. Keep away from the well pump while flooded, and have an electrician or well contractor check the wiring and pump before switching it back on.

3. Disinfect and test the well

Once the water has gone down and the pump is safe, a flooded well usually needs to be pumped out and shock chlorinated. Penn State Extension notes that shock chlorination is designed for one-time contamination events, and a flood is one. See shock chlorinating a well. Your health department may offer free or low-cost testing after a declared disaster. Test for total coliform (and E. coli) and nitrate at a minimum, plus anything else the health department recommends for your area. Don't return to drinking the water until tests are clean.

4. Go easy on the septic system

While the ground is saturated, the drainfield can't absorb wastewater, and the system may back up. Use as little water as you can until the water table drops. Don't pump the tank while the ground is still flooded. An empty tank in saturated soil can shift or float out of the ground, and pumping won't help anyway because the drainfield is the bottleneck.

5. If sewage backed up into the house

EPA advises avoiding contact with sewage, because it may contain harmful pathogens, and contacting your local health department for guidance. People cleaning up should wear protective clothing such as long rubber gloves and face splash shields. After cleanup, wash all equipment, tools, and clothing, as well as the flooded area. EPA recommends disinfecting exposed items and areas with a mixture of 90% water and 10% household bleach, then letting the area dry thoroughly and leaving it unused until it has been completely dry for at least 24 hours.

6. Have the septic system checked

Once things are dry, have a septic professional inspect the system. Floods can leave silt and debris in the tank, damage pumps and alarms, and erode soil over the drainfield. Systems with electrical parts need them checked before they're powered up.

Before the next flood

Know where your well, tank, and drainfield are, keep the well cap sealed and above grade, keep a supply of bottled water, and store records somewhere safe. Our checklists cover the basics.

If the power is out too

A well pump needs power, and storms that flood often cause outages. The outage prep checklist and well pump generator sizing on our sister site Generator Watt Calculator cover running a pump on a generator safely.

Cleaning up a sewage backup safely

EPA's guidance for sewage that backs up into a home is specific:

• Avoid contact with the sewage, because it may contain harmful pathogens.
• Call your local health department or onsite wastewater agency for guidance.
• Wear protective gear during cleanup: long rubber gloves and a face splash shield at minimum, plus boots.
• Disinfect exposed areas and items with a mix of 90 percent water and 10 percent household bleach.
• Wash everything used in the cleanup afterward, including tools, equipment and clothing.
• Dry the area completely and don't use it until it has been completely dry for at least 24 hours.

Throw out porous items soaked with sewage, such as carpet padding, upholstered furniture and mattresses, if they can't be professionally cleaned. Keep children and pets out of the area until cleanup is finished.

When the ground is still saturated

A septic drainfield can't work when the soil around it is waterlogged. Wastewater has nowhere to go and may come back into the house. Until the water table drops:

• Use as little water as possible: short showers, no laundry and no dishwasher.
• Don't have the tank pumped while the ground is saturated unless a professional advises it. An empty tank in flooded soil can shift or float out of the ground.
• Watch for slow drains or gurgling. These are signs the system is still flooded.
• Keep off the drainfield. Wet soil compacts easily under vehicles or equipment.

Testing the well before you drink

CDC recommends testing well water whenever there are problems near your well, such as flooding, and whenever the water's taste, color or smell changes. After a flood:

1. Don't drink or cook with the well water until it has been disinfected and tested. Use bottled water, or water boiled or disinfected following EPA's emergency guidance.
2. Have an electrician check the pump and wiring if the wellhead was underwater.
3. Shock chlorinate the well once floodwater recedes. See our shock chlorination guide.
4. Test for total coliform bacteria and nitrate using a state-certified lab, and retest to confirm results stay clean.

Before the next flood

• Know where your tank, drainfield and wellhead are, and keep a map. See how to find your septic tank.
• Make sure your well cap is watertight and the casing extends above expected flood levels.
• Ask your septic professional whether a backflow preventer on the house sewer line makes sense for your home.
• Keep a few days of bottled water on hand.

Key takeaways

• Treat floodwater and sewage as hazardous, and disinfect with a 10 percent bleach solution.
• Don't use the septic system heavily until the ground dries.
• Disinfect and test the well before drinking from it.
• Have the septic system inspected once conditions return to normal.