Houston Health Department
Flood Response Questions and Answers
What are the risks from consumption of and/or prolonged contact with contaminated flood water?
Surface Water (Lakes, Rivers, and the Ocean)
Significant waterborne outbreaks of disease have
not been seen following floods in the United States. However, large
quantities of sewage, chemicals, and other hazardous materials can be
released into surrounding oceans, lakes, rivers, canals, and storm
water retention ponds following floods and power outages. These same
contaminants may also be present in flooded areas that are not normally
covered with water such as streets, residential structures (e.g.
basements), or drainage ditches. Potential health impacts for some of
these contaminants are outlined below. Prevention is the most effective
method for avoiding health consequences from contaminated water
following floods. If possible, you should avoid contact (e.g. drinking,
inhaling, swimming, walking/wading, etc.) with potentially
contaminated water following a flood. If you cannot avoid the water,
wear personal protective equipment such as boots and gloves. Wash
thoroughly with soap and water after contact with flood waters.
Wells and Potential Contamination
How do I know if my well water has been contaminated after flooding?
It is best to assume that your water has been contaminated until proven otherwise. If the top of your well casing has been covered over by flood water, there is a possibility that contaminated water may have seeped into the well. If you have a well where the top of the well casing does not project above the ground and the area has been covered with flood water, you should assume that the well is contaminated.
How can I clean up my well?
You should follow the normal procedures to disinfect your well, following the well instructions. However, remember that chlorine disinfection does not remove chemical contamination from your water. Disinfection only kills bacteria and viruses. For instructions, see the CDC page on disinfecting wells at https://emergency.cdc.gov/disasters/wellsdisinfect.asp.
Treating water for drinking
How can I treat my water?
Use commercially bottled water if available . If commercially bottled water is unavailable, and if you have electricity or gas or even a campfire to heat water, boiling is the best way to kill bacteria, viruses, and parasites in water. Bring the water to a rolling boil for one minute. Remember that boiling will NOT remove chemical contaminants. If you suspect or are informed that your water is contaminated with chemicals, you should seek another source of water such as bottled water that has not been exposed to flood water.
If you cannot boil your water, you should filter
and then treat the water. For best results, let cloudy, murky,
or colored water settle before filtering. To filter the water, pour it
through a clean towel or t-shirt. This helps to remove particles
and debris, such as soil (mud). You then should treat the filtered
water with chlorine tablets, iodine tablets, or unscented household
chlorine bleach (5.25% sodium hypochlorite). If you are using
bleach, add 1/8 teaspoon or 8 drops per gallon if the water is clear or
¼ teaspoon or 16 drops per gallon if the water is cloudy, murky,
colored, or extremely cold. Mix the bleach in the water and let it
stand for about 30 minutes before using it.
Water that smells “off” may be contaminated with
chemicals. If you are concerned about whether your water is
contaminated, you should look for another source of water such as
bottled water that has not been exposed to flood water. Filtering
and treatment with chlorine or iodine will not remove chemical
contamination from the water.
More specific information on potential risks from flood waters is discussed below.
Diarrheal Illness – viral, parasitic, and bacterial
Why should I be concerned about diarrheal illness in a flood situation?
Significant waterborne outbreaks of disease have not been seen following floods in the United States. However, some diarrheal illnesses can be spread easily when people are living or working in crowded conditions, especially if they are exposed to contaminated flood water that may contain human or animal waste.
What are the diarrheal disease-causing organisms that are most likely to contaminate floodwaters in the United States?
The most common waterborne diarrheal disease-causing organisms in the United States are Shigella, norovirus, Escherichia coli O157:H7, Cryptosporidium, and Giardia. These are all pathogens (germs) that may already be present in untreated groundwater in many states. During normal, non flood situation, the water treatment process removes them from the water you use for drinking, cooking, and washing. In an emergency response situation when water treatment facilities may not be functioning at full capacity, there is a substantial risk that these pathogens (germs) will spread among populations in shelters, camps or temporary housing unless the sanitary facilities are adequate and soiling with feces or vomit is rapidly cleaned and disinfected. These pathogens (germs) may cause waterborne outbreaks or epidemics if many people drink contaminated water. Food prepared by infected persons, or food prepared with sewage-contaminated water, can also spread infection.
How can I protect myself from diarrheal-disease causing germs that may be in the flood waters?
The best ways to prevent yourself from getting sick are to wash your hands frequently and thoroughly, with soap and clean water, and to not drink, cook, or prepare food with contaminated water. The management and specific prevention of each of these diseases is beyond the scope of this document. However, the risk of most diarrheal infections is reduced if people have access to 1) clean treated water that is stored safely so hands cannot dip into it, 2) safe food that is thoroughly cooked, is distributed and served in a sanitary way, and the leftovers promptly refrigerated in shallow containers or discarded, and, critically, 3) clean and functioning toilet facilities and handwashing facilities that include running water, soap, and single-use/disposable towels to dry hands. People should minimize contact with or ingestion or inhalation of potentially contaminated flood waters.
More information on safe water in an emergency situation can be found on the CDC website:
For more information about the specific organisms mentioned above, see the home page for each one on the CDC website:
The CDC website also has an informational page for other germs you might have concerns about.
How likely is it that I will get Hepatitis A?
The risk of hepatitis A virus transmission is very low. Hepatitis A outbreaks have not occurred following other floods in other parts of the country, including the massive Midwestern floods of the late 1990's. Thus, even though the water and sewage systems are damaged or out of operation, the risk of a hepatitis A epidemic generally is considered to be very low.
How do I get Hepatitis A?
An outbreak of hepatitis A will not occur unless someone infected with the virus is present, and the circumstances of exposure permit transmission. Hepatitis A virus is not found in pets, rodents or creatures that live in the ocean or freshwater. It cannot reproduce itself outside the human body. The virus is transmitted by the fecal-oral route. This means that the virus is excreted in feces, and can be transmitted if contaminated feces gets into the mouth of someone who has never been infected before.
How sick can I get with Hepatitis A?
The disease tends to be more serious for adults than children. Approximately one third of the U.S. population is already immune to hepatitis A virus infection. Many people had the infection as children, and many more have been vaccinated. Hepatitis A vaccination is required before you can attend school in many states. People cannot have a chronic hepatitis A infection, and persons who become infected are immune for the rest of their lives.
How do I keep myself from getting Hepatitis A?
Having access to safe food and water will prevent foodborne or waterborne Hepatitis A. Boiling water will inactivate Hepatitis A virus as well as many other disease-causing germs. Washing hands, cooking food thoroughly, and ensuring that persons with hepatitis A do not prepare or serve food for others will prevent foodborne hepatitis A.
For more information about hepatitis A: https://www.cdc.gov/ncidod/diseases/hepatitis/a/index.htm
Why should I be concerned about wound infections in a flood situation?
The skin serves as a protective shield for the body by preventing the entry of germs. The risk for injury and wound infections during and after a natural disaster is high. When skin wounds occur, they can allow entry into the body of germs like Staphylococcus, Vibrio, Aeromonas, Clostridium (tetanus) certain fungi, and Pseudomonas. These organisms can cause many symptoms, ranging from mild inflammation to severe, life-threatening infections. The risk of wound infections is increased when an open wound is immersed in flood water and other potentially contaminated sea- or fresh-waters.
How do I protect myself from a wound infection?
Thoroughly wash any new wound with clean water and soap. If you have a wound, keep it clean, dry, and covered with a clean bandage. Avoid immersing the wound in potentially-contaminated water. Monitor the wound and seek medical care if the wound becomes painful, red, warm, swollen, or if red streaks appear or you develop a fever.
Will a tetanus shot protect me from wound contamination?
A tetanus shot will only protect you from tetanus. There are many other infectious organisms that can enter broken skin or wounds and cause inflammation and infection. If you have an injury, consult a health care provider to determine if you need a tetanus booster and what other treatment may be appropriate.
What is a fungal infection?
A fungal infection is a mold or fungus that grows on your skin. Fungal infections are more common in damp, moist climates and living conditions, and are spread easily when many people are sharing living situations. The most common fungal infections are often known as tinea, athelete’s foot, or jock itch.
How do I prevent a fungal infection?
If possible, you should wear plastic shoes that you do not share with anyone else when you are showering or walking around your living space. Dry your body completely after washing and wear loose clothing that allows the air to move freely around your skin.
How do I get treated for a fungal infection?
Fungal infections can be treated easily with over-the-counter and prescription medications.
For more information on fungal infections, see the CDC website:
Should I worry about chemical contamination of my drinking water or of the flood water?
It is possible that your drinking water, or the flood waters, have been contaminated by chemicals. These could include fertilizers, pesticides, or industrial and manufacturing chemicals.
What are the symptoms of chemical exposure?
The symptoms of exposure to different chemicals can vary, depending on the chemical. In general, symptoms of chemical exposure progress can vary from objectionable odors and taste to irritation of the skin, eyes, nose throat, or respiratory tract. Dizziness and headaches are also fairly common with many chemicals. It may be several days or weeks before some symptoms show up.
How do I prevent health effects due to chemical exposure?
The best way to avoid health effects due to chemicals is to avoid the exposure. Avoid walking barefoot or in sandals, especially if you must walk through flood water. If your drinking water has an odd taste or smell, you should seek another safe water source.
How is chemical exposure treated?
If you think you have been exposed to toxic chemicals, the first step is to avoid future exposure if possible. Some chemicals are poisons that have specific antidotes. In cases of severe exposure, delivery of these antidotes may be time critical. For other chemicals, it is best to get away from the source of exposure and let the body clean the chemical out of your system naturally.
What is Leptospirosis?
Leptospirosis is an infection of both humans and animals. It is caused by bacteria called Leptospira. In humans it causes a wide range of symptoms. Some infected persons may have no symptoms. Others may have high fever, severe headache, and muscle aches. In severe cases, people may have jaundice (yellow skin and eyes) from liver failure. Severe disease may also cause kidney damage and respiratory distress. In rare cases death occurs. Many of these symptoms can be mistaken for other diseases. Leptospirosis is confirmed by testing of a blood or urine sample.
How do I get Leptospirosis?
People get leptospirosis from exposure to infected animal tissues or to soil or water contaminated by infected animal urine or tissues. The disease is not spread from person to person. Many different kinds of animals carry Leptospira. Animals may carry the bacterium but have no symptoms. Leptospira have been found in cattle, pigs, horses, dogs, rodents, and wild animals. Urban leptospirosis caused by exposure to rats occurs in the United States. Outbreaks of leptospirosis have occurred following flood events.
How do I prevent Leptospirosis?
The risk of getting leptospirosis can be reduced by avoiding contact with urine-contaminated water. Protective clothing and footwear should be worn if exposure to urine-contaminated water is unavoidable.
For more information about leptospirosis: https://www.cdc.gov/ncidod/dbmd/diseaseinfo/leptospirosis_g.htm
Other Diseases Unlikely to Occur in the United States
Can I get cholera from the flood waters?
The risk of cholera is extremely small in the United States. For cholera cases to occur, the organism that causes cholera (toxigenic Vibrio cholerae O1 or O139) must be present, and people would have to consume water or food contaminated with it. The organism is currently extremely rare in the Western Hemisphere. From 1998 through 2006, only 20 persons have acquired cholera in the continental United States, and almost all of them had a history of eating shellfish or other seafood that may have been raw or undercooked.
How can I protect myself from cholera?
Without someone who has cholera to introduce the organism into the water supply, you cannot get cholera. Boiling or chlorinating water will inactivate Vibrio cholerae and many other disease causing germs that may be present. Cooking fish or shellfish thoroughly and discarding leftovers that cannot be promptly refrigerated will prevent foodborne cholera.
I’ve heard that I can get cholera from the bodies
of people or animals who died in the flood, or when graveyards are
flooded. Is that true?
While the presence of cadavers is distressing and problematic for many reasons, they cannot be a source of cholera unless they themselves were infected with it. The organism will not be present in the bodies of cholera victims who died long ago.
Other prudent general precautions are outlined on the CDC website: https://www.bt.cdc.gov/disasters/hurricanes/index.asp
Can I get typhoid fever from the flood waters?
The risk of typhoid is extremely small following floods in the United States. An outbreak of typhoid fever will not occur unless someone infected with the organism is present, and the circumstances permit transmission. The organism that causes typhoid fever, Salmonella Typhi, has the human as its only host, and it does not persist in the environment. The risk of typhoid fever transmission is higher than that for cholera, but still is very unlikely. Typhoid outbreaks have not occurred following hurricanes or floods in the United States, including the massive Midwestern floods of the late 1990's. Thus, even though the water and sewage systems are damaged or out of operation in many areas, the risk of a typhoid epidemic is extremely low.
How do I protect myself from Typhoid fever?
Providing safe food and water will prevent typhoid fever. Boiling or chlorinating water will inactivate Salmonella Typhi germs and many other disease causing germs. Cooking food thoroughly and discarding leftovers that cannot be promptly refrigerated will prevent foodborne typhoid fever.
Other prudent general precautions are outlined on the CDC website: