NC State Extension Publications

Introduction

Floodwaters can contain debris that can damage drinking water wells and cause them to become contaminated with chemicals and bacteria. If your well was submerged or you suspect that the well may be contaminated, DO NOT drink the water. After the flood waters recede, drinking water wells should be 1) inspected for damage, 2) purged of contaminated water, and 3) disinfected.

Drinking water wells are best repaired and disinfected by a well or pump contractor. If the well is not damaged, many homeowners can purge and disinfect their water systems themselves. The Centers for Disease Control and Prevention (CDC), the US Environmental Protection Agency (US EPA), and the Water Systems Council provide important and useful guidance for this process. This guidance is intended to supplement information issued by state and local health authorities. Below are a few highlights.

Please note: If you suspect that your well might be contaminated with chemicals or do not feel confident inspecting, purging, or disinfecting your well, do not hesitate to contact your local or state health department or local extension agent for specific advice on your well.

Inspect the Well

First, think safety. A risk of electrocution, falls, and injury exists near wells as floodwaters recede.

  • Turn off all electricity to the well area before clearing debris, preferably shutting it off at the circuit breaker box. Do not attempt to repair the water system unless you are experienced with this type of work; electrical shock can occur. It is best to have the pump and other electrical components checked by an electrician since damage may have occurred. There will need to be power at the site when the electrician checks the system; they can turn the circuit back on as needed.
  • Carefully inspect the area around the well for hazards such as power lines on the ground or in the water, open holes, slippery conditions, and other debris (sharp metal, glass, or wood). Also look for snakes, black widow spiders, fire ants, and other wildlife that may be sheltering near the pump.
  • For dug wells, do not enter the well pit. Gases and vapors create a hazardous environment. For severe cases involving any type of well – for example if the top cap came off the well and debris entered – it is recommended that a well contractor be contacted to pull the pump and clear the well pipe. Many well contractors also have the ability to put a camera down the well to check for internal damage.

Purge the Well

Once the well is safe and operational, it should be purged. This is a simple step, where the nearest outside faucet is used to flush the water from the well until it runs clear. Be sure that the purged water is discharged such that the contaminated water will not flow back into the well.

Disinfect the Well

Multiple steps are involved when disinfecting a well and household water lines using chloride bleach (sodium hypochloride). It is very important that you read all instructions and cautions for disinfecting wells, which are detailed in these documents from the US EPA, CDC (for bored/dug wells or for drilled/driven wells) and by the Water Systems Council.

It is important to use only unscented household liquid chlorine bleach, most of which are in the 5-8.25% concentration range. The CDC documents give more precise measurements of how much chlorine bleach should be used based on well diameter and depth. If this is unknown, follow the US EPA recommendation of 1 gallon. Always use protective goggles or a face shield when working with chlorine solutions, work in well-ventilated areas, and avoid breathing vapors. Note that chlorine solutions may irritate skin and damage clothing.

Once the chloride bleach is added and the well casing adequately rinsed, you will turn on the indoor faucets until you smell the scent of bleach, then shut off all of the faucets. It is very important to wait 12-24 hours before turning the faucets back on. This will allow enough time for disinfection of the entire system to occur. Do not drink, cook, bathe, or wash with this water during the disinfection period, as it will contain unsafe levels of chlorine.

After 12-24 hours, turn on all faucets to flush the residual chlorine from the lines; then, your water should be safe to use.

IMPORTANT: If your water smells like fuel or has a chemical (non-chlorine) odor, then disinfection has not made your water safe for drinking. Contact your local health department for specific advice.

Wait 7-10 days following disinfection to have the water in your well sampled for bacteria. Testing will not yield accurate results until all traces of chlorine have been flushed from the system. Contact your local health department about getting the test, or see this article for information about having your drinking water well tested.

Because groundwater moves, it is possible that the well can become re-contaminated several months after the flood. It is a standard recommendation that wells be tested annually. With the flood, the recommended testing frequency is increased. This is especially true if any strange odors or tastes develop.

Authors

Area Specialized Agent, Water Quality/Waste Management
Onslow County
Associate Professor and Dept. Extension Leader
Biological & Agricultural Engineering

Publication date: Oct. 1, 2016

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