On July 21, Multnomah County and city officials warned Portlanders that their drinking water had tested positive for E. coli and they should boil water from westside taps before drinking it. Panic ensued. 

People swamped stores to buy bottled water, and some restaurants shut down until the warning was lifted the next day.

Those fears were stoked further by news reports. When the boil order was lifted, KPTV reported that the tap water was "safe to drink again." The Oregonian questioned why the Portland Water Bureau waited more than a day after finding the first tainted sample before alerting the public.

In fact, Portlanders were never in any danger. 

The boil-water notice was not a crisis but—if anything—an overcautious cry of "Wolf!"

Here's what really happened.

On July 19, workers for the Portland Water Bureau took routine samples from the 16.4 million-gallon open-air Reservoir No. 3 at Washington Park in Southwest Portland; the Water Bureau generally takes between 10 and 20 samples each day.

Two different samples tested positive for coliform bacteria, a type of bacteria common in animal feces. The first tested positive for E. coli. A second sample, taken the next day, tested positive for coliform bacteria of a less dangerous type. The day after that, July 21, officials issued their warning. 

Dr. Gary Oxman, health officer for Multnomah County, says no one was in any serious danger and that the warning was a prudent, preventative measure. 

"I would classify it as a low, low risk," Oxman says.

WW wondered what exactly the risk was—and what it would actually take to poison the city's water supply.

So we asked the experts—doctors, epidemiologists and engineers. Here's what we learned:

  1. Probable number of live coliform bacteria in the July 20 water sample that triggered the boil-water alert, according to the Water Bureau’s water quality manager, Rich Giani: 1.
  1. Number of that same bacteria U.S. Department of Agriculture regulations allow in a 4-ounce stick of butter: 1,100.
  1. What that lone coliform bacterium probably was, according to city and county officials: Harmless.
  1. Number of the other six samples the Portland Water Bureau took July 20 upstream, downstream and at the original sample site that also contained coliform bacteria: 0.
  1. Why this lonely bacterium caused the Portland Water Bureau to issue the boil-water notice, according to Water Bureau administrator David Shaff: Federal regulations require it.
  1. Why the Water Bureau went ahead and drained Reservoir No. 3: As an added precaution.
  1. Number of previous boil-water notices issued since the current warning system was instituted in 1990, according to county health officer Oxman: 1, in 2009.
  1. According to Giani, the number of positive E. coli samples found since 2009, after the Water Bureau switched to a more sensitive “presence-absence” testing system: 4.
  1. Number of illnesses known to have been caused by E. coli in the water supply after those instances, according to Oxman: 0.
  1. Last year in which Portland had a water-associated disease outbreak: 1954.
  1. Distance a small amount of E. coli would generally travel within a chloramine-treated water system (such as Portland’s) before being killed, according to Giani: “A couple blocks.”
  1. Amount of toxin it would take to poison the water supply, according to William Lambert, epidemiologist at Oregon Health & Science University: “Truckloads and truckloads.”
  1. Date by which all open-air reservoirs must be capped or replaced by closed reservoirs, by federal mandate: 2020.
  1. Cause of most recent contamination: Unknown.
  1. Number of bears it would take defecating in the reservoir to cause a disease outbreak, according to Oxman: Many, many bears defecating continually, or “one bear that had just the right organism, defecating repeatedly.”