Water Supplies: Make Safeguards Go with the Flow
In the Spring of 1993, Milwaukee was staggered by the nation's largest outbreak of waterborne disease. Cryptosporidium, a protozoan, passed undetected through two water-treatment plants and, once it reached customers' taps, caused more than 400,000 illnesses (mostly diarrhea) and between 50 and 100 deaths out of some 800,000 customers who drank the water. Crypto is often present in mammal feces, and so might have come from a nearby sewage plant; authorities never figured out what happened. But a principle was established: pathogens in water supplies can kill.
There are about 168,000 public-water systems in the United States, some serving 8 million people and some serving 25. To thwart a repeat of the Milwaukee poisoning, security has been stepped up around the country's water supplies. Since Sept. 11, the local Coast Guard has been patrolling the area of Lake Michigan where Chicago's water intake is located. New York City has increased the number of daily samples it takes at 900 sites from 2,060 to nearly 2,500, blocked off some roads that traverse reservoirs and stationed armed guards at "critical sites" (authorities prefer not to be specific). Helicopter surveillance, including the use of night-vision goggles, has been stepped up in New York's 2,000-square-mile watershed, where hunting, fishing and hiking permits have been suspended, says Charles Sturcken of the city's Department of Environmental Protection.
If security at the water supply fails to deter terrorists, the next line of defense involves not technology or security, but simple dilution. "Approximately four dump-truck-loads of sodium cyanide mixed into a 1 million-gallon reservoir are required to yield a lethal dose to users," says Jeffrey Danneels of Sandia National Laboratories. Large systems typically draw on stores of 3 million to 30 million gallons, making a high-casualty chemical attack very unlikely. Although giardia, cholera and crypto all survive in open water, exposure to the ultraviolet radiation in sunlight kills salmonella and some other pathogens.
If contaminated water reaches the treatment plant, disinfection is the next line of defense. Chlorination, used in most every municipal system, kills or inactivates viruses as well as bacteria like E. …