Whether you have just had the well head open for inspection, you have had work done on the well or well head, flood water has recently submerged your water well, or you have decided to start using a well that has sat dormant for a period of time… you
really should disinfect the well before use!

Below you will find a simplified list of instructions on how to properly disinfect a drinking water well.  Please keep in mind, though, that all wells have differences and no two well water situations are exactly alike.  So, if this list does not provide you with enough guidance, contact your local environmental department and they can usually provide you either with more detailed instructions on their web site or the names of reputable, licensed well water professionals in your area.

  1. Pump water from the well before disinfecting allowing all sediment, debris and other visible ‘junk’ to flow out of the well.  Leaving that stuff in the well during the disinfection process diminishes the cleansing effect of the chlorine bleach.
  2. Add unscented chlorine bleach (on other words, just plain old laundry bleach… which usually has around 5% chlorine and no added fragrances) to the well and test the water coming out of the well.  You will want to add enough bleach until testing shows 50 to 100 parts per million (ppm) of bleach in the water.  The chart below will give you an approximation of how much unscented laundry bleach you may need to use.
  3. Depth of Well 3 in. 6 in. 9 in. 12 in.
    50 feet 3 ounces 8 ounces 25 ounces 50 ounces
    100 feet 6 ounces 20 ounces 50 ounces 100 ounces
    150 feet 8 ounces 30 ounces 75 ounces 150 ounces

    After adding the bleach make sure you route the well’s discharge water (the water produced by the well when turned on) back into the well so that the chlorine bleach mixes thoroughly in the well.  Mixing should take place for at least 15 to 20 minutes.

  4. Reconnect the well’s output hose to its normal connection (the one leading to the house) and open all faucets in the house individually.  Once a strong chlorine odor appears, close the tap.  Do this for each tap in the house.
  5. Allow the chlorinated water remain in the well and house lines for no less than 2 hours, and preferably longer if you can.  The longer the chlorine stays in the lines, the better the odds of a successful well disinfection.  Usually around 24 hours works well for this purpose, though some experts say letting the system stand as long as possible makes the most sense.
  6. After waiting no less than 2 hours and hopefully closer to (or longer than) 24 hours, open all taps/faucets in the house and allow the well to pump all of the chlorinated water out.  This step is called flushing the system.  Once the smell of chlorine has gone away, close the taps and your well should be ready for use.
  7. To confirm that the disinfection process has worked, you will want to test water from the well in about a week to see if the source of bacteria still exists down in the well.

Important Note:  The instructions above serve as a rough guide for how to disinfect a drinking water well.  Obviously all wells have idiosyncrasies that make them unique so if the above instructions fail to take your well water situation’s specifics into account, definitely err on the side of caution and seek the assistance of a trained water well professional!

Testing for higher levels of chlorine

We believe the WaterWorks High Range Free Chlorine product works well for this application.  It requires no special testing supplies, reagents or complicated test procedures and detects up to 120 parts per million free chlorine.

Free chlorine versus total chlorine?

When disinfecting a water well, you will normally want to test for free chlorine since a ‘stable’ free chlorine residual typically means a water sample no longer contains a significant number of biological contaminants.

High Range Free Chlorine Test Strips