Aqua-Terror: Don't drink the water.

MANY LIBRARIANS were appalled when the call came from the federal government: Destroy all copies of a CD containing a U.S. Geological Survey document with information on public water supplies. Officials assured the librarians that the step was vital to protecting Americans against looming terrorist threats.

The notion that we'll suddenly find our drinking water delivering death instead of refreshment is among the more baroquely unsettling of post-9/11 fears. But is the threat to our water supply serious enough to wipe the historical record? The House of Representatives appears to think the problem is at least worth throwing some money at. In December, it passed a bill that would dedicate $120 million to assess our water systems' vulnerability to terrorist assaults.

The water treatment and delivery industries themselves have long been abuzz about bioterrorism. The Water Quality Association (WQA), a trade group for the water treatment industry, has admitted that it has never bothered to test whether typical treatment procedures could handle the sort of exotic toxins or bioweapons that terrorists might wield (although the WQA suspects current systems probably would do the job in most cases).

Yet the consensus among industry insiders seems to be that terrorists would most likely get far more bang for their buck by aiming their villainy elsewhere--at least when it comes to contaminating our water supply. On the other hand, assaults aimed at destroying water mains or treatment plants to disrupt the flow of water could be singularly devastating, especially when combined with arson. But the threat raises no water-specific security issues. As with any structure, only vigilance, guards, and barricades could prevent such attacks.

By contrast, the deadliness of contaminants added to reservoirs or water sources would most likely be neutralized by dilution and standard water treatment. Downstream contamination generally would require sophisticated pumping devices to inject mass quantities of a poison against the water pressure, and it would only hit limited numbers of consumers, not entire cities.

Tampering outside the treatment plant with chemical additives like fluoride and chlorine would be the best bet for wouldbe killers. But standard monitoring devices that measure the proper levels of those additives probably would quickly alert the plant to such adulteration.