The A.P. analyzed a federal database of water violations over the past ten years and found California had the most violations in the U.S.
Most of the cases involved schools with wells and near farm communities.
The most common toxins are coliform bacteria, lead, copper and arsenic.
The A.P. says the problem has gone largely unmonitored by the federal government.
The A.P. analyzed a database from 1998 to 2008.
The report says California recorded the most violations with 612, followed by Ohio (451), Maine (417), Connecticut (318) and Indiana (289).
In the farming town of Cutler, school officials complain they can't do anything about it because of the recession and the state budget crisis.
AP contributed to this report.