New York City’s drinking water system erupted into the streets yesterday, disrupting the morning rush by flooding subway lines and a swath of the Upper West Side around Lincoln Center.

The flood snarled traffic and caused bus detours.

But the water main break also spotlighted the chronic problem lurking below the city’s streets: the labyrinth of water mains — some of which are more than a century old and prone to leaks and cracks — train tunnels and other old equipment that make up one of the world’s largest networks of subterranean infrastructure.

[Subway service was disrupted after a water main break on the Upper West Side.]

When the flood came

The break occurred around 62nd Street and Broadway just before 5 a.m., halting subway service along a stretch of the No. 1, 2 and 3 lines in Manhattan. It also created floodwaters up to a foot deep along parts of Broadway and Columbus Avenue, from West 61st Street into West 65th Street.

A lake of brown water lapped at the steps of Lincoln Center, and more than a half-million gallons flooded nearby subway tracks up to the rails.

Flooded streets mean problems underneath them

To understand how the break could affect the subway, one must realize that water mains and train tunnels share space underground with a sprawling tangle of sewer mains, power cables, gas and steam lines and telecom wires.