Neglecting to disinfect your well after a flood can have dire consequences on your health. In some cases it could even KILL you.

Rising and swirling flood waters pick up a tremendous amount of waste, debris and other unwanted drinking water contaminants. As those waters recede and dry ground reappears, all of the junk and crud swept up by the flooding gets deposited on all surfaces — including the equipment used to draw fresh drinking water from drinking water wells.

Taking the time to properly clean and disinfect well equipment after a flood will help to prevent the accidental introduction of flood water contaminants into wells if you have to open the well cap in the future.

Also, it takes only the slightest breach in the seal of your well head to allow potentially harmful bacteria, dissolved metals, nitrates, nitrites, etc. access to your drinking water supply.

So, after flooding, or twice a year (as recommended by drinking and well water experts) it makes sense to clean off the well head area thoroughly and disinfect the well itself using some form of chlorine.

Looking for a quick and dirty disinfection method? Not necessarily the best way to go, but any amount of disinfecting beats performing no disinfecting, right? Right.

The South Dakota Department of Health suggests allowing a well to spend a minimum of 8 hours in direct contact with water containing at least 50 ppm of free chlorine. From what we read, it would seem as though they would actually prefer people allow a well to sit, undisturbed, with at least 50 ppm of free chlorine for a longer period of time, such as from sundown to sun up. ( source )

One could use unscented household bleach which contains an average of a little over 5% of hypochlorite solution (remember that free chlorine concentration domes from hypochlorous acid and hypochlorite ions). We cannot stress enough that one should use UNSCENTED bleach for disinfecting a well or other drinking water source!

As a general rule, health officials suggest adding the following amounts of unscented bleach solution to a well for each 10 feet of water it contains if it has an inner diameter of…

  • 2 inches — add 1/4 ounce of bleach
  • 4 inches — add 3/4 ounce of bleach
  • 6 inches — add 2 ounces of bleach
  • 8 inches — add 3 1/2 ounces of bleach
  • 10 inches — add 5 ounces of bleach
  • 12 inches — add 1 cup of bleach
  • 18 inches — add 2 1/4 cup of bleach
  • 24 inches — add 3 3/4 cup of bleach
  • 36 inches — add 8 3/4 cup of bleach

Lift the well pump, add the bleach solution, lower the well pump back in place, and allow the treated well to sit for at least 8 hours. Do not turn on any faucets or do anything else that would draw water from the well.

Once the waiting period has ended, turn on all faucets and allow the water to run until the smell of chlorine has vanished.

Get the water tested for bacterial contamination within a day of disinfection by a certified water testing lab in your area. After flooding many health departments team up with local labs to provide discounted bacteria in well water testing for local residents.

We, of course, would suggest having the well’s water tested for other critical water parameters at the same time since regional flooding can certainly have other effects on the quality of water coming from aquifers.

What about well water disinfection kits?

For those who would like a bit more instruction and procedure when disinfecting a drinking water well after a flood, or twice a year as suggested by many well water professionals, kits such as the Well Safe Well Sanitizer Pack will work very well.

This particular well disinfecting kit contains chlorinating pellets, chlorinating granules, and step-by-step instructions to to guide users through the process of treating a well.

Products like Well Safe have uses down in the body of a well, inside a well’s storage tank, throughout the plumbing between a well and connected buildings, in a cistern sanitation system, etc.

Moral of the story

Clean and disinfect/sanitize your well before returning it to use after local flooding!

Well Safe Well Sanitizer
Well Safe Well Water Sanitizer Pack

Earlier we mentioned that a well ought to sit undisturbed with at least 50 ppm of free chlorine and since we get asked this all the time, we will go ahead and tell you how you can test easily for free chlorine levels that high — without fancy (expensive) test equipment or complicated testing procedures.

For the task of testing higher levels of free chlorine residuals we suggest products like the WaterWorks High Range Free Chlorine Test Kit which has the ability to detect free chlorine concentrations between 0 ppm and 120 ppm in a matter of a few minutes.