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The Hidden Danger of Floods

The Hidden Danger of Floods


Beyond the immediate chaos and destruction of mass inundation, the dangers of flood water carry a host of other hazards in their wake. The greatest impact to water supplies are the disruption of water purification and sewage disposal systems, overflowing of toxic waste sites, and the dislodgment of chemicals previously stored above ground. This can quickly contaminate drinking water supplies with a toxic stew of chemicals and bacteria. 

Let's take you through the hidden dangers of floods to help you understand the risks to your drinking water supply after the high waters recede. 

    Table of Contents:

    How Do I Know if My Water Is Contaminated After a Flood?

    While suspended sewage and oil slicks are clear indications of contamination, it is important to consider all water after a flood unsafe until it is explicitly deemed otherwise by local authorities. 

    Floodwater is contaminated no matter what it looks like. Because of this, drinking water wells can become contaminated from inundation of floodwater laced with toxins, chemicals, septic seepage, and municipal sewage.

    What Are the Risks of Contaminated Floodwater?

    A major risk with floodwater is its potential to harbor bacteria from damaged sewage infrastructure (including septic tanks) that might infect people with potentially life-threatening infectious diseases.

    Common pathogens and viruses include:

    • E. coli
    • Salmonella
    • Hepatitis A
    • Typhoid
    • Tetanus

    Coastal flooding with an influx of ocean water may also bring diseases like Vibrio—a highly dangerous “flesh-eating” disease sometimes contracted by people following hurricanes. 

    The Center for Disease Control (CDC) advises that if you are in a flooded area, you should avoid or limit direct contact with contaminated water. Exposure to contaminated floodwater can cause:

    • Wound infections
    • Skin rashes
    • GI illness
    • Tetanus
    • Melioidosis (along the Gulf Coast)

      In addition to pathogens and viruses, agricultural and industrial chemicals can be swept up into the floodwater mix by traveling over fields and streets.

      How Do Floodwaters Impact Water Supplies?

      While direct contact with floodwater will put you at the highest health risk, floodwater's toxic mix threatens drinking water sources (both surface water and groundwater).

      Public Water Systems

      Impacted public water systems will issue advisories to its customers and remain in constant communication as things develop. But, as we mentioned earlier, it's a good idea to consider your water unsafe to drink until informed otherwise. Floods can impact small water systems the hardest. The CDC recommends that you bring water to a rolling boil for at least one minute in order to kill major waterborne pathogens before using potentially-contaminated municipal tap water.

      Private Well Owners

      Concern is particularly high for those with private wells, where drinking water is at risk of mixing with contaminated floodwater. Swiftly moving floods carry debris that can dislodge well hardware, allowing contaminated water and sediment to enter into your well system. This can even lead to a total collapse of your well. As private well contamination is not monitored by the government, residents are usually left to fend for themselves.

      The EPA has prepared a handy guide on what well owners should do after a flood. Key points include:

        • Avoid turning on your pump after floodwaters have receded. Electric shock can occur. 
        • DO NOT drink or wash with your well water. 
        • Drilled, driven, or bored wells are best disinfected by a well or pump contractor due to the difficulties of thoroughly disinfecting these types of wells  

      What to Do if You Encounter Floodwater

      While the risks of floodwater are significant, there are also simple precautions you can take to protect yourself.

      As we mentioned above, avoid direct contact with floodwater if you can help it. Additionally, it is critical that you see a doctor about cuts, open wounds, and all symptoms of illness

      Lastly, have your drinking water tested by a certified laboratory.

      Testing Your Water

      For private well owners, testing your water is a vital step before resuming normal use. 

      Tap Score's Total Microbiology Water Test is a comprehensive pathogen and microbiological screening service for advanced identification and enumeration of thousands of species of bacteria, protozoa, algae and more in tap water, well water, and other surface water.

      Additionally, persistently wet environments are ideal for toxic mold growth, which can develop in just a matter of days. It is crucial to test your home for mold if you’ve experienced flooding at home.

      What's the Takeaway?

      • Floodwaters can disrupt water purification and sewage disposal systems, overflow toxic waste sites, and then dislodge chemicals previously stored above ground. This can quickly contaminate drinking water supplies with a toxic stew of chemicals and bacteria.
      • Both the EPA and CDC advise those in an area affected by flooding to consider all water after a flood unsafe until it is explicitly deemed otherwise by local authorities. Contact and/or ingestion of contaminated floodwater can cause an array of life-threatening illnesses.
      • Well owners are particularly at risk and should have their water tested by a certified laboratory prior to resuming use. Additionally, toxic mold growth on affected surfaces is a significant issue to test and address.
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        About The Author


        Johnny Pujol, CEO of SimpleLab, is devoted to advancing environmental laboratory logistics, ensuring each stage—from sample collection to results—is clear, easy, and insightful. Holding a Master's in Engineering from UC Berkeley and a Bachelor's in Economics from Boston University, Johnny brings a unique blend of technical expertise and business insight to his role. Outside of SimpleLab, you can find him training for Pentathlons or writing spy fiction.
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