The drinking water in more than 1,000 public school buildings in New York City went at least a decade without getting tested for lead, according to a WNYC analysis of city data. Only in the last month, according to officials, has the school system begun a comprehensive program to test those buildings, and those results are just beginning to trickle in.

The analysis found that overall, more than two-thirds of the public school buildings have not been tested since 2005. Many of the other buildings have never been tested, according to the data, because they were constructed after a nationwide ban on lead plumbing went into effect and weren't considered at risk for lead contamination. Some others house pre-kindergarten programs that began operating just in the past two years. 

New York City's testing history does not violate any federal rules — the Environmental Protection Agency imposes no lead testing requirements on most public schools — and many other districts around the country may have tested just as infrequently, if not more so. But Marc Edwards, a professor of civil and environmental engineering at Virginia Tech who has been studying the Flint water crisis, said contamination from lead pipes is likely to grow worse over time, not better.

“The conventional wisdom used to be that the plumbing lead release would only get better with time," Edwards said. “And so, back in the day, when schools sampled once and they went in and fixed all the problematic fixtures, they thought was this problem was done forever. We now know that this conventional wisdom is completely wrong."

Edwards said schools that seemed fine 10 years ago could have developed problems since then and recommended that schools test their water annually. 

In most cases, the municipal water, whether in Newark or New York City, is not contaminated. But old school buildings contain lead pipes and fixtures that can corrode, polluting the water with small pieces of poisonous metal. Lead, whether from paint, soil or drinking water, has been linked to brain damage, learning disabilities and other conditions if consumed over a period of time, particularly by children. 

City Hall spokeswoman Amy Spitalnick said the city did not find any cases where school drinking water caused elevated blood lead levels in public school students last year. 

WNYC's analysis was compiled from data behind a lookup tool the city launched last week where concerned parents could learn about when their children's school was last tested. A City Hall official confirmed the numbers, although in some cases offered slightly different figures. In those cases, WNYC used the more conservative numbers. 

A total of 739 public school buildings still operating today tested negative for lead when New York City began testing in 2002, according to the analysis. They were not tested again. Another 338 buildings had at least one sample with an elevated lead level. City officials said they removed the problematic plumbing and, according to the data, most of those buildings tested negative in 2004 or 2005. But they had not been tested again until this spring.

Officials also said the water in many schools has been flushed weekly throughout the past decade to remove lead. 

Roseann Ciarlante, co-president of the parent association at P.S. 10 in Brooklyn, said the city shouldn't have waited so long. Her school's water was tested in 2004, when three of the 16 samples had elevated lead levels.

"Obviously there should be ongoing lead testing in all of our schools, because the health and safety of our children is of the utmost importance," she said. 

Joseph Graziano, a professor of environmental health sciences at Columbia University, said he had a high confidence in the quality of the city's drinking water, but agreed that the Department of Education should have re-tested sooner.

"It does seem like quite a long time," he said in an email. "We are due." 

City Hall spokeswoman Spitalnick said the city's protocols have long met or exceeded EPA guidance, but "We're going even further out of an abundance of caution."

The re-testing that began this month will include public school buildings constructed after the lead plumbing ban went into effect. 

Questions about the quality of the drinking water in public schools across the country were raised earlier this month after test results showed that about half of all of Newark's schools had at least one elevated lead sample. The Newark public school system tests the water in each school building every year. When one is shown to be contaminated, it institutes a protocol that requires repairs, filtering and flushing.

New York City school officials decided recently to re-test every five years. Schools with elevated lead levels will have more frequent sampling.  Dr. Philip Landrigan, a professor of pediatrics at Mt. Sinai Hospital, said he thought that was sufficient.

"I think it's a very good thing that going forward, it's going to be every five years," he said. "I think that will maximize protection now that the issue of lead in drinking water has come to the fore."

Spitalnick said one-third of the buildings had already been re-tested and that the online lookup tool would be updated as new results became available.

Beth Fertig and Matthew Schuerman contributed reporting to this story.

CLARIFICATION: An earlier version of this article said that in the round of water testing that began in 2002, "338 buildings showed elevated levels of lead." This text was updated at 11:45 a.m., March 30, 2016 to say "338 buildings had at least one sample with an elevated lead level."