There are two major types of intentional threats to our water systems, reports this article in our special "Security" section.

Intentional threats against water supplies have been recorded since the earliest archeological and biblical reports of well poisonings. A recent report analyzed terrorist activities reported in the past not just against water systems, but all other targets. This analysis indicates that the numbers of threats and acts of sabotage against water supply systems are relatively small and that hoaxes are much more likely.

There are two major types of intentional threats: 1) destruction of parts of a system, either by physical destruction or by computer hacking, and 2) contamination of the system with various chemicals, microbes, toxins or radioactive compounds.

Destruction of a Water Supply System. Although no water treatment plant or major pumping station will survive direct hits by missiles, explosives on a more modest scale can interrupt the electric power supply, destroy one or more pumps, cause large leaks in reservoirs or dam failures, and generally disrupt parts of the water delivery system. Such attacks, although rare, have occurred. Cyber attack against various computerized components of water supply systems also is possible, including attacks against the supervisory control and data acquisition system. The President's Commission on Critical Infrastructure Security considered cyber threats against utilities to be a primary concern. The trend toward downsizing and automation of systems appears to be accelerating.

Intentional Contamination of Water Supplies. A water supply system may in theory be intentionally contaminated by chemical and radioactive compounds, infectious agents and toxins. Examples of chemical agents are nerve agents, cyanide, arsenic and nicotine. Of the three, nerve agents are obviously the most dangerous, whereas cyanide and arsenic are a lesser threat because of their relatively low toxicity. The most likely points of attack for intentional contamination include posttreatment storage reservoirs, distribution reservoirs and water mains.

At the recent National Symposium on Medical and Public Health Response to Bio Terrorism, there was general consensus that the list of bioweapons of greatest concern was relatively small and consisted of (in decreasing order of concern) anthrax, smallpox, plague, tularemia, botulinum toxin and viral hemorrhagic fevers such as Ebola. Most speakers stressed the probability of an air release via an aerosolized bioweapon and considered attacks on water supplies much less likely owing to the effects of dilution and treatment.

However, scientists for the U.S. Army who examined the potential threat of biological warfare agents to potable water concluded that on the basis of existing weaponization, stability in water, and known or potential resistance to chlorine, some of the bacterial agents (e.g., anthrax, Clostridium perfringens, plague) and all of the biotoxins (e.g. botulinum, aflatoxin, ricin) were potential waterborne threats. However, they also noted that the dose required to cause a health effect was so high that contamination would have to be targeted close to the consumer. For example, the infectious doses for cholera and typhoid are on the order of a million organisms that would have to be contained in a 200-milliliter glass of water. At this level they can be easily detected within minutes - if, of course, one is looking at them.

Contamination of a water supply by radioactivity is possible, with accidental releases considered to be the primary route. Monitoring for radioactivity in a water supply system often focuses on monitoring of the potential discharge sources by the industries themselves. However, the intakes also may be monitored. Natural sources of radioactivity also can threaten a supply. The U.S. Geological Survey, the U.S. Environmental Protection Agency and the American Water Works Association recently have been investigating the components of gross alpha radiation that may be due to short-lived alpha emitters such as radium-224.

The main lines of defense against physical and cyber acts of destruction and contamination include the design of a redundant water treatment and distribution system and denial of access. A single treatment plant, a single long supply line and a single source of electrical power are prone to disruption by vandalism, terrorism or acts of nature, such as lightning, earthquakes and floods. Although the destruction of major pipes will disrupt service, pipes usually can be repaired within days. The destruction of motors and pumps at major pumping stations is disastrous because repairs may take months. Therefore, a water supply should be highly redundant and flexible; i.e. many components might fail, but the system should still be able to function at some level. Larger systems should have multiple treatment plants, multiple storage reservoirs and a well-connected distribution system with many loops. For example, some plants in Europe, notably those situated downstream of rivers with high pollution risks, can interrupt their intake for extended periods (up to several weeks) because of the presence of intermediate storage facilities and/or multiple, independent intakes.

A key line of defense is to prevent physical access by unauthorized persons to a free water surface, as in a reservoir. Storage reservoirs in distribution systems may be particularly vulnerable. In underground reservoirs, the ventilation devices must be constructed in such a way as to not allow a person to pour anything into the reservoir. An above-ground reservoir with roof hatches should not have ladders on it that allow climbing. In addition, the hatches should be secured. The intakes, pumping stations, treatment plants and reservoirs should be fenced to secure them against casual vandalism. Beyond that, there should be intrusion alarms that notify the operator than an unauthorized person has entered a restricted area. An immediate response may be to shut down a part of the pumping system until the appropriate authorities determine that there is no threat to the system.

Assuming that a terrorist overcomes these physical barriers, the next line of defense, at least for microbial contaminants, is chemical. Most bacterial pathogens have been reported to be destroyed by common disinfectants such as free chlorine or chloramines. Thus, the second line of defense is to maintain a chlorine residual of about 0.5 mg per liter free chlorine in the distribution system and to increase it in times of perceived or real danger. Although it is possible to deactivate chlorine by adding sodium thiosulfate, this would require large amounts and a reliable injection system. In systems with a high/variable level of dissolved organics, maintaining a high chlorine residual is problematic and may even be counterproductive. Also, many nonbacterial pathogens are resistant to chlorine and the effectiveness of disinfectants on some biowarfare microbes is not known. The use of chlorine also must be balanced with concerns about the formation of chlorinated byproducts.

This article is provided through the courtesy of International Life Sciences Institute. It is excerpted from "Early Warning Monitoring to Detect Hazardous Event in Water Supplies," edited by Thomas Brosnan.