Flooding is the most frequent natural disaster and the chances are high that you will likely experience at least one major flood in your lifetime.
Because floods can cause contaminated water to get into wells, it is not safe to drink well water after a flood: the well must be disinfected before you can use water from it.
Ideally, you would have a professional disinfect the well. However, this isn’t always possible – especially if you live somewhere remote or the flooding was so widespread that professionals are overbooked.
For this reason, it’s very important that you know how to disinfect a well yourself.
Note: You should still test it before drinking. Until the well water has been tested, it’s advised that you boil the water to disinfect it before drinking.
You can also use bleach to disinfect water.
How to Disinfect a Well
1. Wait until the floodwater recedes and power is restored.
2. Mix bleach (5.25% to 6%) with water. Use these amounts:
- 1 cup bleach in 5 gallons of clear water.
- 2 cups to 1 quart of bleach in 10 gallons of clear water.
- 2 quarts of bleach in 20 gallons of clear water.
- Most wells require 2 quarts of bleach mixed with 10 gallons of water.
- See the table below for how much bleach your well requires.
3. Pour the bleach mixture into the well. If possible, use a hose to run the mixture down the inside of the well casing. Aim to get the entire inside of the well casing wet with the mixture for at least 15 minutes. Replace the well cover when finished.
4. Turn on all water taps and spigots in your home, sheds, garage, yard, etc. Start with the taps which are furthest away from the well. Keep the taps open until you can smell chlorine.
5. Turn the taps off. Do not use the water for 8 hours.
6. Open all taps and spigots again. Keep the taps open until you cannot smell chlorine anymore.
*You should never flush chlorine water into streams, lakes or other natural bodies of water. Ideally, you should also not flush chlorine water into your septic system. However, if you must, make sure you flush the water at a very low flow rate so the septic system doesn’t get overloaded.
How Much Bleach to Use for Disinfecting a Well
| Depth of Well (ft) | 4” Casing | 6” Casing | 8” Casing | 24” Dug Well | 36” Dug Well | 48” Dug Well |
|---|---|---|---|---|---|---|
| 5 | 1 cup | 1 cup | 1.5 cups | 4 cups | 3 quarts | 5 quarts |
| 10 | 1 cup | 1 cup | 1.5 cups | 3 quarts | 6 quarts | 2.5 gallons |
| 15 | 1 cup | 1 cup | 1.5 cups | 4 quarts | 2 gallons | 4 gallons |
| 20 | 1 cup | 1 cup | 2 cups | 5 quarts | – | – |
| 30 | 1 cup | 2 cups | 4 cups | – | – | – |
| 40 | 1.5 cups | 2 cups | 1 quart | – | – | – |
| 60 | 2 cups | 4 cups | 2 quarts | – | – | – |
| 80 | 2 cups | 1 quart | 2 quarts | – | – | – |
| 100 | 3 cups | 1.5 quarts | 2.5 quarts | – | – | – |
| 150 | 4 cups | 2.5 quarts | 4 quarts | – | – | – |
https://www.health.state.mn.us/communities/environment/water/wells/natural/disinfectflood.html
https://www.cdc.gov/disasters/wellsdisinfect.html
https://www.cdc.gov/healthywater/emergency/drinking/private-drinking-wells.html
https://www.in.gov/localhealth/portercounty/files/welldisinfection_201305311715036621.pdf
