In August 1982, 500 New Englanders were evacuated [1] after residents' reports of bubbling and hissing sounds coming from their toilets and faucets were followed by two explosions. A propane and water mixture seeping from their pipes had contaminated the entire town. It wasn’t a terrorist attack, but the same process that prompted hundreds of New Englanders to evacuate could be used to launch a widespread terrorist attack, according to the Department of Homeland Security (DHS).

For months DHS has warned about possible attacks on utilities infrastructure. Earlier this month, DHS and the Interagency Threat Assessment and Coordination Group issued a bulletin [2] advising local agencies to be aware of a terrorist tactic aimed at contaminating drinking water. The bulletin was published online Monday by Public Intelligence. Through a relatively simple process, a chemical or biological agent could be deposited into the water supply and spread over long distances without immediate detection.

“Over the last decade, violent extremists have expressed aspirational interest in contaminating unspecified water supplies, and as recently as July 2011 specifically raised backpressure as a means of contamination," the bulletin states. But while experts agree that the potential for a backpressure attack exists, existing measures may already be enough to thwart a potential attack.

Backpressure contamination comes from the reversal of the normal flow of water systems, with the water picking up contaminants as it flows backward. Unintentional backpressure incidents can occur for a number of reasons.

“When you lose pressure in the public water system, like if a water main breaks, anything that is in that line will get siphoned back into the water line…so it’s not an uncommon thing,” said Roy Dillard, a director at the American Backflow Prevention Association [3]. “Backpressure happens when there is a pressure, higher than the city water pressure, exerted on the water systems and it causes the water to flow backward.” 

It’s exactly what happened to the town in New England that August. A narrative of the incident is featured in the most recent edition of Stop Backflow News: Case Histories and Solutions [1], a report published by Watts Water Technologies.

Repairmen had connected an industrial propane tank to a fire hydrant to purge the defective tank before starting repairs. Because of the tank’s higher pressure, propane vapor forced itself into the pipes and contaminated the whole town’s water supply.

Using backpressure, attackers could launch a relatively widespread attack with similar results, using minimal tools and expertise, according to DHS. The agency says terrorists could use backpressure to intentionally distribute contaminants throughout the public water system, causing an instant public health emergency in addition to leaving a lasting economic and psychological impact.

DHS says police and firefighters should be aware of indicators of a potential backpressure attack. These include vehicles other than fire trucks being hooked up to fire hydrants, signs of tampering with water pipes in commercial buildings, and discolored water, water odors, or decline in water quality. A medical indicator: a burning throat after drinking water.

Dillard says a backpressure attack wouldn't be impossible, but the threat may be overstated because of several redundancies built into the existing water systems to protect from both backpressure and contaminants.

“It’s possible. Virtually any kid taking a high school science class could figure it out, but it would have to be done in such volumes that it would be relatively hard to do because of the fact that we use backflow prevention assemblies in major areas and almost all of your industrial areas,” he said.

If terrorists tried to use a biological agent, Dillard, a tap water enthusiast, said the chlorine in water would most likely take care of it. “That’s what we keep the chlorine for, to keep the nasties out. It also keeps dysentery and cholera out of our water systems."

Dillard said he thinks DHS probably released the bulletin as a reminder to remain vigilant around water systems and utilities infrastructure.

Additionally, all 50 states require controlled cross-connections or backflow prevention [4] systems, and 32 states have active backflow prevention programs. “Our water systems are pretty well protected,” Dillard said.

If a person does notice something suspicious about their water, like strange smells or tastes, they should contact their local water purveyor and ask if there’s been any accident in the area or incidents reported, Dillard said.

Diagram via screenshot of Watts Water Technologies report
Photo by crawfish head/flickr [5]
 

Thumbnail: