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What is the problem?

Disruption of drinking water supplies or flooding that covers plumbing fixtures can lead to back-siphonage of dirty water into home plumbing and into the home or building. Contamination of buildings can occur when sewage or septic systems back up in homes and businesses. When flood waters rise and contact sewage in buildings, the flood waters become contaminated and can travel to other structures, spreading the contamination. This type of contaminated water is commonly referred to as brown or black water. It is assumed that all flood waters are brown or black water and are contaminated with disease-causing organisms. Materials contaminated with brown or black water present an acute health risk if not properly cleaned and remediated. Disease may be caused by viruses, bacteria, protozoans and worms, either in the flood water or deposited on materials that have been contacted by flood waters.

What are the hazards and what can they do?

  • Exposure & Health: Human waste contains many organisms that have the potential to cause disease. These organisms reside in the digestive tract and intestines of people, sometimes causing no adverse health effects to the person carrying the organism in their body. These people are referred to as “carriers” of the disease. Human carriers exist for all types of diseases. In any given population where certain diseases are prominent, a proportion of individuals will excrete the disease-causing organisms, or pathogens, in their feces.
  • Viruses: Viruses are parasites that reproduce only within the cells of another organism. Hepatitis A is an example of a virus which is commonly found in wastewater. Hepatitis A causes liver disease. Signs and symptoms of hepatitis include loss of appetite, fatigue, nausea, pain and yellow jaundice. Other viruses present in wastewater may attack the central nervous system, skin or the heart.
  • Bacteria: Bacteria are a normal part of the digestive system and assist in the digestion of food. Escherichia coli is a common organism used to monitor for fecal contamination of water supplies. Other bacteria have the potential to cause intestinal infections such as gastroenteritis (stomach upset) and dysentery (diarrhea). The most common symptom of a bacterial infection of the intestines is diarrhea.
  • Protozoans: Intestinal parasites that are protozoans exist as one-celled organisms or as a cyst, a hard, protective covering. There are two common protozoan intestinal parasites of particular concern, both of which are transmitted in cyst form through food, water or other items that are contaminated with feces and ingested or placed into the mouth. Both forms cause symptoms including diarrhea lasting one week or more accompanied by abdominal cramps, bloating, flatulence, fatigue and weight loss. There is a one- to two-week incubation prior to the onset of symptoms. Immunosupressed people may be at risk of life-threatening dehydration from serious diarrhea. Children are also at increased risk of dehydration from severe diarrhea. These organisms are commonly found in day care centers where mouthing of objects occurs by diapered children.
  • Worms: Helminths are parasitic worms that generally do not reproduce in the human body. The number of worms infecting a person is usually restricted to the actual number of eggs ingested. The severity of symptoms is also related to the number of worms, with heavy infection having symptoms of anemia, digestive disorders, abdominal pain and debility. Worm eggs are passed in the feces and may enter the body through food, water or other items that are contaminated with feces and ingested or placed into the mouth.

Disease transmission factors:

Infection of wounds that break the skin is a more common problem associated with exposure to contaminated flood waters than the occurrence of the intestinal diseases outlined above. Follow good personal hygiene and seek prompt medical care for any wound on the skin that may be contaminated with flood waters, wastewater or fecal matter. The most common source of Clostridium tetani, the bacteria which causes tetanus, is human feces. Infectious strains of E. coli such as antibiotic-resistant E. coli may also be present in contaminated waters.


Any sewage backup or contact with contaminated waters must be properly cleaned to minimize the risk of disease. Floors should be cleaned with a 10% bleach solution (or other comparable commercially available disinfectant). Contaminated carpets should be replaced or cleaned by a professional cleaning contractor. Caution must be exercised not to mix bleach with any other household cleaners. Contaminated skin should be washed thoroughly with warm soapy water for a minimum of ten (10) minutes. It is recommended that contaminated laundry should be bagged and disposed of properly. If cleaning is attempted, these items should be washed separately in hot water with a 10% bleach solution. Some professional cleaners may be able to clean contaminated clothing. Persons with weakened immune systems are at increased risk from exposure to brown or black water.

If you are served by a public water system, you should flush all water lines, including hot water lines, thoroughly. Check with your water company to see if they are disinfecting the water lines. You may notice a strong odor of chlorine while this is occurring. If you have a private well, call an electrician to ensure it is safe to turn the well pump back on. Have a licensed plumber or well driller disinfect your well, and have it tested before using the water for cooking, drinking or washing.

Storm water:

Children should not be allowed to play in or around storm water collection drains or outfalls, nor should they be allowed to swim or play in water of questionable origin. In some locations, during periods of heavy rain, storm water systems may become contaminated with raw sewage overflows. Additionally, storm water runoff may be contaminated with fecal matter from pets or agricultural animals which is capable of transmitting many of the diseases outlined above.


  • Hammer, M.J. and M.J. Hammer, Jr. Water and Wastewater Technology. Prentice Hall, Inc. Englewood, Cliffs 1996.
  • Benson, A.S. (ed.). Control of Communicable Diseases Manual. American Public Health Association, 1995.

Last Reviewed: July 12, 2004