By Kelly A. Reynolds, MSPH, Ph.D.

In a previous On Tap column (March 1999), biological warfare was described as a fictional scenario where public water supplies were tainted. Recent events confirm that bioterrorism is no longer a threat but a reality. While we put trust in the government to protect the mass population and secure the safety of food and water as well as the airways, there are further defenses that individuals can arm themselves with to avoid becoming a victim of biological contaminants. Should municipal water supplies become contaminated, are you prepared? Do you know what to do?

Biological weapons are defined as any infectious agent used intentionally to cause harm to others, including groups of viruses, bacteria, protozoa or fungi and also chemical toxins produced by microbes, animals or plants. There appears to be no shortage of sources for bioterrorism agents with 453 known repositories in 67 nations—many having little security against dissemination. Examples of potential biological warfare agents are listed in Table 1. The most commonly feared organisms today are the same as those listed decades ago, i.e. Clostridium botulinum (botulism toxin), Bacillus anthracis (anthrax), Yersinia pestis (plague) and Variola virus (smallpox). Left untreated, the mortality rate of these organisms is quite high, averaging better than 60 percent each. Aerosolization is typically the preferred route of exposure for biological warfare organisms but contamination of the food and water supply is also a potential transmission route.

Feared agents
Anthrax was first detected in 1850 with a vaccine developed in 1877. The Bacillus anthracis organism will attack any mammalian host, making it a choice pathogen for livestock and human destruction. As a pore, it’s capable of survival in the environment for many years and may cause disease by ingestion, inhalation or cutaneous exposure. Anthrax spores are relatively resistant to heat and chemical disinfectants, with a disinfection time of 200 minutes in chlorinated water (1 part per million chlorine). They are large rod-shaped organisms from 1-1.5 microns (mm) in width and 4-10 mm in length.

Bacterial toxins are a more likely choice for a saboteur of water. C. botulinum organisms are widely distributed in soil and often found in intestines of mammals, birds and fish. Adverse exposure effects are usually due to an intoxication of the preformed botulism toxin that’s also susceptible to heat. Botulism toxin is three million times more potent than the chemical nerve agent sarin, which was used in terrorist attacks in Japanese subways in 1995. To put this in perspective, the U.S. Congressional Office of Technology Assessment claims that a person drinking less than a half cup of untreated water from a five million liter reservoir would become severely ill, and possibly die, if the water had been contaminated with just ½ kilogram (kg) of Salmonella typhi, 5 kg of botulism toxin or 7 kg of staphylococcal toxin, whereas 10 tons of potassium cyanide would be required to produce the same level of toxicity.1 Biological organisms may linger or actually multiply in the environment, thereby enhancing their effects. Stock cultures are relatively easy to obtain and many are even naturally present in the environment. Furthermore, propagation requires only basic skills in microbiology. In addition, transport of small quantities of the infectious agent is simple, since no airport metal detectors can detect a “biological bomb.”

For a skilled scientist, current technology enables the production of genetically engineered organisms capable of specific control and use. Genetic engineering could open a large number of possibilities, modifying normally harmless, non-disease- producing organisms to become highly toxic and/or untreatable. Although genetic engineering requires some scientific background, this type of weapons development could easily take place under the guise of medical or microbiological research.

Water—an unlikely route
Water isn’t an efficient means of delivering a biological weapon. Unlike other nations, U.S. water supplies are numerous (approximately 168,000 public water systems) and generally self-contained. The dilution effect of water would require large volumes of pathogens to be introduced. Furthermore, conventional treatment practices in the United States are highly effective at removal of pathogens and their toxins from water. Water treatment systems are able to kill or inactivate many biological pathogens through a multiple-barrier approach. Bacteria, protozoa and spores are largely removed by conventional water treatment practices such as flocculation, coagulation and filtration. In addition, use of disinfectants is effective at removing bacterial and viral pathogens. Granulated activated carbon (GAC) filtration is also effective at removing chemical contaminants.

Due to contamination in the distribution system and treatment failures, however, pathogens are frequently found in finished (treated) drinking water, suggesting a vulnerability of the water supply to a deliberate biological attack. While a large scale water contamination event affecting large populations borders on the impossible, individual neighborhoods or small populations are still at risk. In addition, the same practices aimed at protecting consumers from such attacks don’t always protect against everyday contaminants found in finished water (recall the Milwaukee Cryptosporidium outbreak in 1993—104 dead, 400,000 ill).

Recent update
The House Subcommittee on Water Resources and the Environment held a hearing, nearly a month after the Sept. 11, 2001 attacks, on risk and prevention of terrorism against U.S. water resources. In addition, U.S. Environment Protection Agency Administrator Christine Whitman announced establishment of a water protection task force aimed at helping federal, state and local partners expand their tools to safeguard the nation’s drinking water supply from terrorist attack. Although many believe water isn’t an attractive target of terrorism, others choose to err on the side of safety and prepare for the possibility of an event. At the very least, an attempted attack could cause widespread terror, economic impacts and a loss of public confidence in water distribution facilities.

Water utilities across the nation have been on a state of high alert since Sept. 11. Added security ranges from patrol boats and armed guards monitoring watersheds to satellite imagery of reservoirs. Researchers at the Department of Energy’s Sandia National Laboratory developed a monitor used to detect the presence of contaminating chemicals in water. Originally designed for underground monitoring chemical waste spills, the system produces results in real time. Notification systems are already in place in the United States should an emergency response be necessary. This system was developed through a partnership with the Association of Metropolitan Water Agencies and the FBI to alert authorities and the public about vulnerabilities and incidents.

Methods of prevention
Today, an entire arsenal of biological organisms exists that can be spread by food, water or air to unsuspecting victims. Although boiling of water supplies is generally a reliable way to destroy pathogens in drinking water, there’s often no reliable warning method of a biological warfare attack. Therefore, personal defense readiness is advised. Remember that the first knowledge of an attack is likely to be a large number of victims. Since most biological organisms require an incubation period prior to the onset of symptoms, and initially produce very common symptomology, many more victims may be exposed by the time the first generation is identified. The need for earlier warning is among the factors for ongoing development of the National Drinking Water Contaminant Occurrence Database (NCOD), mandated by the 1996 Safe Water Drinking Act Reauthorization (see

Military personnel are routinely trained in defensive awareness to biological warfare. Elaborate respirators and fully contained suits have been standard issue in previous war situations. Personal detection and decontamination kits for certain chemical agents have also been developed. Treatments for biological agents include avoidance, barrier resistance, vaccines and antibiotics. Vaccines are available to protect against botulism, anthrax, smallpox and the plague, but aren’t given to the general public as a matter of course.

Although conventional municipal water is highly effective for most biological contaminant concerns, system failures are known to occur. In addition, many cities rely on water supplies that aren’t filtered or disinfected. Furthermore, a contaminant could in effect be introduced in the water distribution system post-treatment, leaving the end-point consumer vulnerable. Although you’re more likely to be struck by lightening than become a victim of a bioterrorist attack, you still don’t stand under a tree during a thunderstorm. In other words, there are some simple practices that can offer increased protection from microbial contaminants.

Point-of-use (POU) filtration systems provide the means to eliminate virtually all biological warfare agents. Many chemical contaminants are very easily removed by inexpensive and widely available carbon filters. POU systems, rated for removal of waterborne biological agents, are available in a range of sizes from individual use to those capable of delivering thousands of liters of water per hour. Common filtration media and treatment methods have proven effective including diatomaceous earth and carbon filtration, reverse osmosis (RO), boiling and others.

Activated carbons are probably the most widely applied adsorbents for removal of chemicals from water and air, or for the decontamination of surfaces by adsorption. The carbon particles can be mixed with chemical reactants or reaction catalysts to actually detoxify the offensive agent. Carbon can also be regenerated after use by heat treatment or chemical desorption. Ultraviolet light (UV) is an effective disinfectant of most of the waterborne pathogens discussed here, and functions without use of chemicals. Used in combination with filtration and disinfection technology, UV, RO and/or water softeners can help consumers avoid the vast majority of biological warfare agents in water.


  1. Office of Technology Assessment, 1991:

About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds also has been a member of the WC&P Technical Review Committee since 1997.

EXTRA—Fighting bioterrorism
Here are a few additional information resources on the effort to contain the threat of bioterrorism:


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