After a flood, leave the septic tank alone until the field drains

EPA's question-and-answer page offers some comfort at the start: "Most septic tanks are not damaged by flooding since they are below ground." It also warns that tanks can fill with silt. So the likely problem is water with nowhere to go, and a bad decision can make it worse.

Should you pump the tank right away?

No. In EPA's words, a tank pumped while the field is under water might "try to float out of the ground." The instinct to empty a full tank is strong after a storm, but a full tank is heavy and an empty one in waterlogged ground is the one EPA worries about. Wait for the water to fall first.

When can you use the system again?

EPA's test is the field itself: soil water out there has to drop below the water around the house. Until then, every flush and shower is heading to a field that cannot take it. Plug basement drains if you have them, and cut water use drastically.

A raised house has no basement drain to plug, but the other half of the advice holds. Our story on what to do before you restart anything covers the rest of the house.

What about a system with a pump or alarm panel?

Treat the electric parts as live. Some systems have a pump, control panel or alarm, and those are for a licensed electrician or septic professional once water has touched them. A breaker check is fine only from dry ground, never from a wet floor. Ready.gov's advice is to leave wet electrical equipment alone, and to touch nothing electrical while you are in water.

The video on this page, from an Oklahoma State University water specialist in 2019, repeats the same plain steps: plug drains, limit water, get a professional inspection, and leave opening the system to professionals because of the fumes. It assumes basements and pumped systems and does not say how to shut power off safely, so the advice above stands where the two differ.

How do you know the flood did damage?

You often cannot tell from the lawn, which is why EPA says to have the system professionally inspected if you suspect damage. Silt in the tank will not show from above. The state's signs of malfunction give you something to watch for once water recedes: pooled sewage outside, seepage into a room below ground, or a drain that backs up though nothing blocks it.

Any of those puts a duty on the owner to tell the local authority right away, and repairs wait for its approval. Our story on who approves septic work explains the steps.

Does rebuilding after a storm mean a new septic system?

It need not. The state makes room for an existing system after a catastrophe: it can remain if a licensed professional engineer, acting as the septic designer, puts in writing that it works and complies. Without that paper the exception does not apply, so ask the board of health what comes next.

What if your well flooded too?

Then the well needs its own steps, and the first is simple. EPA's septic page says, "Do not drink well water until it is tested." A flooded field near a flooded well is the pairing that makes this urgent. EPA's separate well sheet also says not to turn on the pump until wiring has been checked, and our well story goes through it.