MEDFORD (AP) — Too much lead is in the water of a Medford elementary school.

School officials say they don’t know why the lead levels spiked, but the federal government requires schools to cut the levels when they rise above a certain amount.

The measurements at Jefferson Elementary in March rose slightly above the limit.

A new plumbing system and drinking fountains were installed in September 2006.

Until recently, school officials say, tests showed lead at acceptable levels.

But as of Monday about 500 pupils and staff members were drinking bottled water until the lead level can be brought down.