Every city has occasional water pipe breaks, but the weekend gusher in St. Paul’s Lowertown area made a bigger splash than most.

The break flooded streets with about 1.75 million gallons of water in about an eight-square block area near the Farmers Market. It caused a major drop in water pressure in other parts of the city, too. The pressure and water safety have been restored, but for a while Saturday, the city urged residents in many areas not to drink the water and then asked them to boil it for three minutes before drinking.

So why was this different than the 100 or so water main breaks that the city sees, and fixes, each year?

“[It was] different largely because of its magnitude. It was on a 20-inch main, while the vast majority of our breaks are on 6-inch mains,” Jim Graupmann of St. Paul Regional Water Services, explained Monday morning.

“The break was also a very large split that caused water to flow out at a great rate; great enough in fact to depressurize our low service system, a significant part of our distribution system.”

This depressurization was extremely rare, he said. The last times it happened were in the 1990s, when the rules for notifying the public were less stringent. So this is the first time that St. Paul Water Services has issued a “Do Not Drink” order because of a main break.

(There was another similar order last year, though, after a power outage caused a depressurization, he said.)

Last month’s big downtown Minneapolis water main break, which spewed 14 million gallons across downtown streets, involved a 3-foot main, and it’s cause was easily explained: a construction back hoe hit the pipe.

The St. Paul break, though, so far remains unexplained. There was  no construction or other apparent activity under way in the area. Other pipes in the system will be examined to see if they might have the potential for a similar rupture.

Graupmann called the downtown break a “double split (a longitudinal break) that was nearly the length of the pipe (16 feet).”

In most other cases, the break happens around the pipe, not along it. He calls that “cracking circumferentially.” he said. That often causes minimal leakage that most nearby residents don’t even notice.

Jodi Wallin, spokesperson for the Water Services, said that in most cases the smaller breaks affect only a one- or two-block area. “The workers are in and out in a few hours, and people in the immediate area are the only ones who are aware.”

And Graupmann emphasized that it was the depressurization of the larger system, and the need for the “Do Not Drink” notice under current Health Department rules, that made it such a major incident.