A California school district said it failed to inform families about the presence of lead in drinking water, which could impact more than 45,000 students.

The Oakland Unified School District in northern California sent a letter to families saying they were not informed earlier about the lead found in nearly 200 drinking fountains and faucets.

“Despite our attention to detail and diligence in managing our campuses, we did not communicate effectively with members of each school community as testing began, as we received results, and as corrections were implemented,” said the letter, distributed by NBC News.

“We are putting systems in place to ensure that a lack of effective communication does not recur and that school communities are notified in a timely manner when such testing occurs on their campuses,” the letter said, according to NBC News.

According to the source, fixtures in the school district – the 11th largest in the state with more than 45,000 students – were tested for lead levels above five parts per billion (ppb).

This baseline is below the state and federal guidelines of 15 ppb.

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The investigation found that 116 faucets had levels above 5 ppb and below 15 ppb, and 70 faucets had levels above the state and federal standard of 15 ppb.

According to the U.S. Environmental Protection Agency, lead exposure is dangerous for children.

“Even low levels of lead in children’s blood can lead to behavioral and learning problems,” the agency explains, adding that lead can cause lower IQ and hyperactivity, slowed growth, hearing problems and anemia.

The agency also points out: “Lead can enter drinking water when lead-containing piping materials corrode, especially when the water has high acidity or low mineral content that causes pipes and fittings to corrode.”

The school district’s statement said, according to NBC News, that “61 fixtures have been repaired so far” and that the process is ongoing.

“Nearly half of schools have been found to have lead in their drinking water,” the National Association of State Boards of Education said, noting that not all states test their water.

According to NASBE, only 13 states have policies for testing drinking water in schools for lead—and no states have policies for testing for lead paint.