Emergency Well Disinfection Guidelines

A hurricane, like Floyd in 1999, can damage structures beyond your home. A hurricane that brings large amounts of rain can ultimately cause flooding. Once the floodwaters recede, the real work begins. While affected residents are cleaning up the damage from a flood, if they get their water from a well, they must also pay close attention to their wells and well water.

If your well was flooded, you need to properly disinfect it and have the water tested before drinking the water. Proper disinfection using granular chlorine or calcium hypochlorite tablets (commonly known as H.T.H or chlor-tabs) is strongly encouraged. However, due to the extreme emergency nature of a flooding event, if granular chorine is not available, nonscented household bleach (5.25 percent liquid chlorine) can temporarily be used to disinfect your well.

If you have any concerns about your water, whether it comes from a well or a public water system, it is recommended that you use boiled, bottled or stored water for normal activities like drinking, making ice, eating and washing hands.

Directions follow on how to properly disinfect your well following an emergency. The two methods of well disinfection – using calcium hypochlorite (preferred) and using non-scented, household bleach – are presented in easy-to-follow steps.

Well Disinfection Procedure

Complete all repairs before disinfecting system. Prevent surface water and near-surface ground water from entering the well in the future. Seal pipes and wires entering the well and seal well-casing joints near the ground surface in bored wells. High concentrations of chlorine in water are toxic. They can burn the skin on contact and cause illness if consumed. Warn all potential water users about these dangers and store the chemicals in a safe place. To safely chlorinate your well, you should use safety goggles, gloves and appropriate clothing. Always follow chlorine product manufacturer's instructions.

Calcium hypochlorite tablets (brand name: H.T.H or Chlor-Tabs) are recommended for the proper disinfection of your well. These tablets are sold at building supply centers, hardware stores, water treatment vendors and swimming pool stores.

1. First, pump your well for about 30 minutes at the wellhead or an outside faucet to remove the most contaminated water.
2. Using one of the charts below, pour the amount of chlorine, either 70 percent calcium hypochlorite (Chart A), or unscented household bleach (Chart B) into the well. The charts indicate the amount of chlorine needed based on the diameter of well casing and depth of water in the well.
3. Connect a hose to the spigot closest to the wellhead. Turn on the spigot and, using the hose, discharge and circulate water back into the well until you smell chlorine in the water.
4. Rinse the well casing and all other equipment in the well with the chlorine water flowing from the hose.
5. After completing steps 3 and 4, turn off the spigot you have used to circulate water in the well. Next, turn on each faucet and spigot in and on the house until you smell chlorine, then turn off and let chlorine stand in the well and plumbing systems for at least 24 hours.
6. After 24 hours, connect a garden hose to an outside faucet and run water through the hose away from the house foundation and any septic tank system until the chlorine smell is gone. Do not pump large quantities of highly chlorinated water into a septic system.
7. After the disinfection process is completed, contact your local health department to have the water sampled. Continue to use bottled water or water that has been brought to a rolling boil for one minute until sample results show no coliform bacteria contamination.

Calcium hypochlorite is preferred for disinfecting wells, but unscented household bleach containing sodium hypochlorite will work in an emergency. When calcium hypochlorite tablets are used, they should be carefully broken into smaller pieces using proper eye protection and rubber gloves.

Pour the broken tablets directly into a bored well. Remove the well air vent and insert the broken tablets through the vent opening in a drilled well.