Is it Safe To Drink Tap Water After A Flood

With water rising as high as 30 feet or more, floods can be incredibly destructive. For those living in flood-prone areas, the aftermath is all too familiar: a bleak landscape filled with debris and trash, streets covered in dirty, stagnant water, unpleasant sewage-like odors, and many other distressing scenes. Regrettably, the impact of floods extends far beyond the immediate damage, possibly having short- and long-term consequences for drinking water. In this article, we’ll look at how floods affect drinking water quality and provide some simple tips to help keep your water safe.

What Causes Floods?

Floods occur when water overflows or soaks land that is usually dry. Generally, this takes hours or days to develop, giving residents time to prepare or evacuate. However, some floods can strike suddenly with little or no warning.

The most common cause of floods is heavy rainfall, often during hurricanes and tropical storms. As the rain pours, rivers may overflow their banks and spread water over nearby land. Similarly, rapid ice melts in the mountains, broken dams or levees, or even beaver dams in vulnerable spots can overwhelm rivers and other surface water sources, flooding surrounding areas.

Things like floating debris or ice can also accumulate at a natural or human-made obstruction and block the flow of the water. The water held back by the debris dam or ice block can cause flooding upstream. If the blockage suddenly breaks, it can trigger a flash flood downstream.

How Do Floods Affect Drinking Water Quality?

Whether your drinking water comes from a private well or municipal treatment plant, flooding can impact its quality—possibly leaving you without clean water for days or weeks. Let’s break down the possible outcomes for both scenarios:

Private Well Users

Private wells are particularly susceptible to contamination from flooding. As flood waters sweep over farmlands, infrastructure, and industrial areas, it can pick up all sorts of contaminants, including:

• Physical Contaminants: Sediment, organic debris (leaves, branches, etc.), petroleum products (oil, gasoline)
• Biological Contaminants: Bacteria (E. coli, coliform bacteria), viruses (hepatitis A, norovirus), microorganisms (Giardia, Cryptosporidium), sewage and wastewater pathogens, radioactive materials (in rare cases)
• Chemical Contaminants: Chemicals from industrial sites, pesticides and herbicides, heavy metals (lead, arsenic, mercury), solvents and hazardous materials, PCBs (polychlorinated biphenyls), dioxins

Water containing these elements can reach well systems not equipped to manage floods, like those that are shallow, damaged, or compromised. The contaminated water can infiltrate the well and jeopardize the safety and quality of the well water. Dug wells, bored wells, and others less than 50 feet deep are more likely to be contaminated, even if damage is not apparent.

Contaminant-laden flood water can also penetrate groundwater resources that supply water to wells. Once the well becomes polluted with raw sewage, there may be a massive spike in biological contaminants like E. coli and coliform bacteria. Consuming water with these and other pathogens can lead to gastrointestinal illnesses and outbreaks of deadly waterborne diseases like typhoid, malaria, hepatitis A, and cholera. Infants, children, older people, and people with low immunity are particularly vulnerable to these illnesses.

Flood waters may also introduce toxic chemicals into your water supply, such as PFAS, pesticides, fertilizers, and industrial pollutants. Furthermore, silt and sediment dissolved or suspended in the water can accumulate in well screens and pipes, obstructing water flow and potentially damaging the well’s infrastructure. And, of course, you’ll likely see a drop in water quality and availability.

People on City Water

While not as vulnerable as well water, there’s also an increased risk of city water contamination during a flood. Floodwaters can quickly overwhelm water treatment facilities and infrastructure, leading to power outages, equipment damage, and significant disruptions to the water treatment process.

Flooding can also damage water distribution systems, potentially causing leaks and breaks in the water main. If broken, these pipeline issues can disrupt the flow of clean water to homes and businesses, allowing pathogens, dirt, chemicals, sewage, or other pollutants to mix with the treated water. Once ingested, these contaminants can cause you to develop waterborne illnesses and other severe health problems.

How Can You Ensure Your Water Is Safe to Drink After a Flood?

As water quality worsens during a flood, so does access to clean drinking water. So, we must safeguard our drinking water quality during these emergencies.

Advice to Private Well Users

People relying on private wells for their water supply should always assume the water is polluted. Even if the well isn’t severely flooded, the water may still be unsafe to drink and use. During floods, contaminated water may enter directly into your underground water source through various pathways like shallow gravel aquifers, nearby wells, abandoned old wells, or other nearby excavations, bypassing the natural filtration process.

Once the floodwaters have subsided, inspect your well for any of the following conditions:

1. Was your well flooded?
2. Is your well situated near flooded areas?
3. Have you noticed any changes in water quality, such as unusual odors, discoloration, or changes in taste?

If any of the conditions mentioned above apply to you, stop using well water for drinking, cooking, and washing and get it tested for coliform bacteria and other disease-causing microbes. While waiting for the test results, you can use bottled water or boil the water from the tap.

Option 1: Boiling. Bring the water to a rolling boil in a pot or use an electric kettle jug (until it automatically shuts off) to kill harmful bacteria, parasites, and other disease-causing microorganisms in the water. Once the water has cooled, it is usually safe to drink. However, drinking boiled well water with high nitrate concentrations (> 10 mg/L) can be dangerous for young children and pregnant women. So, if you suspect nitrate is present or a test confirms it, use alternative water sources, such as bottled water, for cooking, drinking, and preparing infant formula for children six months of age and younger.

Option 2: Using liquid bleach. If boiling water isn’t an option, use unscented bleach to treat your water. Ideally, use liquid bleach that contains 5-6% sodium hypochlorite and avoid those that have detergents/surfactants (i.e., foam up when shaken), fragrances (e.g., lemon-scented), or gel.

To disinfect the water with bleach:

• Add eight drops (approximately 1/8 teaspoon) of plain unscented liquid bleach per gallon (equivalent to 16 cups) of water.
• Stir the mixture well and let it sit for about 30 minutes to allow it to deal with any microorganisms in the water. You should notice a slight chlorine smell in the disinfected water. If you don’t, repeat the dosage and let it stand for another 15 minutes before using. Make sure to use sanitized food-grade containers to store the treated water.
• If the water is cloudy before adding the bleach, add 16 drops (approximately 1/4 teaspoon) per gallon. Follow the same steps as above to disinfect the water. Again, use clean, food-grade containers for storing the treated water.

Please note: This method may not be effective against certain parasites, such as cryptosporidium.

Option 3: Shock chlorination. This involves disinfecting a water system with a concentrated chlorine solution. The chlorine kills harmful microorganisms, breaks down organic matter, and cleanses the entire system to make the water safe for consumption after flooding or when contamination is suspected.

Of course, you can disinfect a well yourself. However, it can be challenging for some wells to get the disinfectant into the well or other parts of the system that need disinfecting. In this case, we recommend hiring a professional to disinfect your well, such as a licensed plumber, pump installer, licensed water system operator, or well driller.

If you decide to take the DIY approach, follow these steps to shock-chlorinate your well:

1. Determine the correct amount of chlorine. A standard guideline is to use 1/2 to 1 fluid ounce of household chlorine bleach for every 100 gallons of water in the well. You can get a more precise recommendation by consulting a water treatment professional or conducting water testing.
2. Prepare the chlorine solution. Mix the calculated amount of chlorine with a few gallons of clean water to create a chlorine solution. Use a clean container and stir until the chlorine dissolves thoroughly.
3. Add the chlorine solution. Pour the chlorine solution directly into the well, ensuring it reaches all parts of the well, including the casing and the water column. You can pour it down the wellhead or through an access port.
4. Distribute chlorine throughout the system. Turn on all faucets, hoses, and outlets connected to the well. Run water from each outlet until you can detect a strong chlorine odor. This step ensures that chlorinated water has reached all parts of your plumbing system.
5. Allow adequate contact time. Let the chlorinated water sit in the well and plumbing system for a specified contact time, usually between 12 to 24 hours. During this time, the chlorine will disinfect the water and well infrastructure.
6. Flush the system. After enough time has passed, flush the entire system by running water from all outlets until the chlorine odor is no longer detectable. This step ensures that you remove excess chlorine from your plumbing and prevent it from reaching your taps.
7. Test the water for safety. Test the well water to ensure the chlorine concentration has returned to safe levels for drinking. A chlorine test kit or a water testing service can help you confirm that the water is free of harmful microorganisms and safe to use.

Option 4: Use a whole-house well water filter with a UV water purification system

While the above measures will kill most microbes, they won’t remove other contaminants that may have entered your well system during or after a flood. For this reason, we suggest installing a whole-house well water filter and a UV water purifier.

Floodwaters can introduce a wide range of contaminants into your well water—not just bacteria and viruses but also sediment, debris, heavy metals, chemical pollutants, etc. This is where a whole-house well water filter comes in! It uses different technologies and filtration stages to provide whole-home protection against non-microbial contaminants that shock chlorination or boiling wouldn’t remove. This improves your water’s taste, smell, and clarity and prevents clogs in your plumbing and appliances.

Add a UV water purification system to the mix, and you’ll have a powerful hybrid system capable of eliminating a much broader range of contaminants. While shock chlorination can address microbial contamination initially, its effectiveness may diminish as new contaminants enter your well. A UV purification system, on the other hand, provides continuous microbial disinfection. It uses ultraviolet light to deactivate and destroy harmful microorganisms like bacteria, viruses, and parasites, ensuring your water remains safe to drink without chemical additives.

Advice to Persons on City Water

If your water comes from a public system, your water utility, local Department of Environmental Quality (DEQ) office, or health department should inform you about any water problems and how to keep your water safe. Sometimes, they might issue a boil water advisory if there’s a chance it has harmful germs. This alert or advisory can be issued via radio, TV, social media, newspapers, or, in some cases, by using door hangers, door-to-door contacts, or signs posted in affected areas.

If you ever need to boil your water, the owner or operator of the public water system should provide clear instructions, including how long to boil it and any other precautions you should take. If you don’t hear anything from your water utility and are concerned about your water quality, call them to find out what’s happening and what actions you may need to take.

Usually, customers of public water systems do not need to test their water, as the public water system operator will conduct these tests. Still, it’s crucial to have a line of defense against harmful contaminants trying to enter your water supply.

Installing a whole-house water filter system is an excellent starting point, eliminating sediment, chemicals, heavy metals, and other pollutants and impurities. But like homes on well water, a UV purification system will destroy any disease-causing bacteria, viruses, parasites, and other pathogens in the water.

Learn more: Difference between nominal and absolute filter

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Translator: Duong Nguyen Hoang Khang