Private wells after flooding

A well draws groundwater from the ground. Normally the soil layers above filter out much of the dirt, and a sealed wellhead stops surface water from running straight in. During a flood both are disrupted: water stands over the wellhead, gets into the shaft through leaks and can also contaminate the surrounding groundwater.

Flood water carries with it everything it picks up on the way: sewage from overflowing drains and septic tanks, manure from fields, soil and often heating oil, fuel or other chemicals. Shallow dug wells and cisterns are usually more vulnerable than deep, well-sealed drilled wells, but these too count as unsafe after flooding.

A flooded well therefore becomes safe again only once it has been cleaned, disinfected, flushed and the water tested. Household treatment such as boiling cannot replace this, because it does nothing against fuels and chemicals.

Stop using the water immediately for drinking, cooking, brushing teeth, ice cubes and food – and tell everyone in the household as well as guests. A note on every tap helps, because out of habit it is easy to take a sip after all.

Then secure replacement water: your stock, bottled water or official distribution points. Using treated well water is an option only if the authority explicitly instructs it.

Next, call the public-health office or the competent body. There you find out how disinfection and sampling should be done, which laboratories test water and what is required in your region. Unlike with the public supply, as a well owner you are usually responsible yourself for making this happen.

The biggest immediate danger is electricity. Do not touch or switch on the pump, controls or cables of a flooded well while they are wet or standing in water. A qualified electrician checks the installation before it goes back into operation.

Never climb into a well shaft. Gases that cause suffocation can collect in narrow shafts, and there is a risk of falling. Work in the shaft belongs in the hands of professionals.

Disinfecting a well, often called ‘shock chlorination’, is done only according to the authority's instructions or by professionals – with the amounts stated there, not self-estimated ones. After that the well is flushed, and the water is used again only after a laboratory result. If oil, fuel or chemicals are suspected, a specialist firm and the authority are needed, not the household.

A holiday home or farm with its own supply was in the flood zone; the water has drained away and clear water comes out of the tap. This is exactly where the temptation to just use it again is strongest. But clarity says nothing about germs or dissolved chemicals – until cleared, it stays off limits.

It can take days or weeks before a well is cleared, and professionals and laboratory tests cost money. A sufficient water stock and knowing where the nearest distribution point is make this time much easier. If the area floods again, the checks start over.

Rules for sampling and well maintenance differ by country and region. The local authority is therefore always the authoritative point of contact.