The lead content of water exceeds federal safety standards at half the elementary schools in Boston tested, according to a preliminary state report, and officials say some affected buildings will get bottled water.

Samples from 40 of the 81 public and private elementary schools show higher levels of lead than the U.S. Environmental Protection Agency's allowable level of 50 parts per billion, according to the Department of Public Health study released Tuesday.

Nineteen schools have levels in excess of 20 parts per billion. The EPA has been considering lowering the maximum level to 20 parts per billion.

Twenty had lead in their drinking water that was less than 20 parts per billion.

Further tests are scheduled to determine the source of the lead.

"This is not an issue specific to Boston," said Brad Prenney, director of the state Child Lead Poison Prevention Program. "It is an issue (that is) state and nationwide."