They erred on the side of duh

Over-abundance of duh.

State water safety standards require the S&WB to issue boil-water warnings if the pressure in the system, which normally is about 60 pounds per square inch, drops to 15 psi. St. Martin said pressure readings -- which are taken at 30 fire stations throughout the city -- never dropped below 16 psi, leaving officials in a quandary.

"We could not determine that, from the time of the initial break until those readings were taken ... if anyone in the immediate vicinity of the transmission main would have possibly had a drop in water pressure below 15 psi," she said.

It's always that last little statistically insignificant increment of measure that ends up being the doozy.