DURHAM - Students returning to class at Durham's Northern High School next week may be provided bottled water after testing on a drinking fountain found lead levels above those considered safe by federal guidelines.

Lead also was detected in the water from kitchen taps at Burton Geo-World Magnet Elementary School and Merrick-Moore Elementary School, though at concentrations below the danger level.

High levels also were confirmed at Y.E. Smith Elementary School, where previous testing found lead in 2004 and students have been drinking bottled water for more than two years.

Durham Public Schools decided to test selected taps at 27 of the system's older facilities after previous rounds of testing by state and local health officials found elevated lead levels in water samples collected from private homes across the city.

It is suspected a chemical until recently used to treat much of Durham's water might have contributed to an increase in the amounts of lead leaching from old plumbing fixtures. The city ceased using the chemical in question, ferric chloride, July 6.

Lead was banned from use in the solder joining pipes in 1985, and buildings constructed after then don't appear to be affected. The oldest sections of Northern High were built in 1953. Burton and Merrick-Moore also date to the early 1950s.

In light of the latest test results, the school system has contracted a private lab to test every tap used for drinking or cooking at every Durham school built before 1990, as well as the downtown administration building. Samples were collected Friday, and school officials said results should be known by the middle of next week. Students return from summer break Friday.

"We don't want to take any chances," said Durham County Public Health Director Brian Letourneau, who is advising the school system. "The best thing to do is test them all."

Based on the results of the expanded round of testing, the school system could mandate the use of bottled water or disconnect selected drinking fountains. Cafeteria staff are being instructed to run the taps at least five minutes before using the water for drinking or cooking, a precaution shown usually effective in flushing out the contaminated water.

The water from the fountain at Northern High had lead levels at 20 parts per billion. The U.S. Environmental Protection Agency classifies readings at or above 15 parts per billion to be unsafe. A second sample collected from the fountain after it was allowed to run for several minutes found no lead.

Durham's water supply has been under scrutiny since April, when a young child was found to have been poisoned by lead after drinking from a faucet in a South Durham apartment. The case is only the second time in state history an incidence of lead poisoning has been linked to tap water.

In a statement issued Aug. 11, the N.C. Division of Public Health advised Durham residents who live in older homes and who have children under age 6 to get their tap water tested for potentially harmful levels of lead. The recommendation for testing also extends to older homes with pregnant women or mothers who are breast-feeding. Exposure to lead has been linked to birth defects, brain damage and developmental problems.

County health officials have also suggested that young children, pregnant women and those nursing should have their blood tested for lead if they live in homes built before 1986, the year after the lead ban took effect.