The cast iron water main that ruptured spectacularly in Northeast Portland on Saturday was more than 100 years old.

Despite that, Portland Water Bureau officials could not predict the failure. The 30-inch diameter pipe was buried under a quiet, narrow residential street with no obvious risk factors, like the weight of a TriMet bus line on the street. Nor were there any apparent leaks before millions of gallons of water suddenly burst through the pavement and flooded the neighborhood.