The Independence Branch of the Free Library usually is flooded with students who flow in after school to use its books and computers.

But last week, amid biting cold, the popular branch on Seventh, between Market and Chestnut Streets, was flooded instead with icy water from a burst sprinkler pipe, soaking the carpeting in the main reading room. The library was forced to close, most likely for a month.

Joe Baker, president of the Friends of the Independence Branch, a private group that raised $200,000 to stock the branch's shelves when it opened in 2001, said the Feb. 11 incident was the third flooding of the library since last summer.

"Aggravated, stressed, disappointed - the whole gamut" was how he described his reaction to the latest dousing, which, unlike the previous two, did not damage books.

He said the first two floods were related to construction in the historic building, the former home of the Balch Institute for Ethnic Studies. The building opened as a satellite of the Philadelphia Free Library in 2001 and quickly became the branch with the highest circulation of the 54 branches in the system, Baker said.

It was renovated last summer to make room for the Constitution High School, a city magnet school affiliated with the National Constitution Center.

Twice during those renovations, Baker said, burst pipes caused extensive damage to books, books on tape, photographs and other items, including a unique collection of books about gay and lesbian civil rights donated by local activist Barbara Gittings. He estimated the damage from the first two incidents at about $40,000.

Much of the Gittings collection was reconstituted from holdings in private collections. The carpeting was professionally dry-cleaned, tested for mold, and pronounced safe, Baker said.

Named for its proximity to Independence National Park, the branch primarily serves Society Hill, Old City, Queen Village, Washington Square West and Chinatown. It is also popular with commuters who work in Center City, which contributes to its high circulation.

Baker did not have a damage estimate on the most recent flooding, which remains under investigation.

But even a temporary closure of the building is devastating beyond its cost in dollars and cents, he said, because the library also serves as a center for community meetings and programs, particularly for the residents of Chinatown.

"That's a loss that cannot be recouped," Baker said. "During the time the library is closed, those programs are just gone."

Contact staff writer Michael Matza at 215-854-2541 or mmatza@phillynews.com.