ARLINGTON – Traces of the anti-anxiety drug meprobamate were found in Arlington's tap water, according to a report released Monday.

Tests on the city's water were conducted in October 2006, but the city did not release results or reveal that it commissioned the tests until recently.

The report's existence was made public in March when The Associated Press released a series of investigative stories that found pharmaceuticals in the drinking water of at least 41 million people in the U.S. .

Julie Hunt, director of Arlington Water Utilities, said the U.S. Environmental Protection Agency hasn't determined what would be a safe or dangerous level of meprobamate in tap water.

However, she said the traces found in Arlington were measured in parts per trillion and would be far below any dangerous level.

Ms. Hunt put the dose of one part per trillion into perspective. "For you to even get an 80-milligram baby-aspirin dosage of that, you'd have to drink a gallon of this water every day for 44,000 years," she said.

Arlington city officials initially declined to reveal the name of the drug found in the tap water or the four others found only in the untreated water supply, citing Homeland Security concerns.

But the Texas attorney general's office ruled this month that Arlington officials did not present sufficient evidence that these results needed to be kept secret.

"You do not argue, nor does it appear, that the test was conducted for the purpose of preventing, detecting, or investigating an act of terrorism or related criminal activity," Assistant Attorney General Jordan Hale wrote to the city.

The city had until Monday to release the documents or sue the attorney general's office. Arlington officials decided not to appeal the ruling.

Mayor Robert Cluck, however, said he's still concerned that someone could use this information to harm the water supply.

Water from the John F. Kubala Water Treatment Plant was found to have meprobamate in a concentration of 1.4 parts per trillion, according to tests conducted by the Southern Nevada Water Authority. The concentration was 1 part per trillion at the Pierce-Burch Water Treatment Plant.

In the untreated water, the level was 3.5 parts per trillion at John Kubala and 2.6 parts per trillion at Pierce-Burch.

That same drug was found in the water supplies of San Diego, Las Vegas and Los Angeles. Ms. Hunt said a report from the Awwa Research Foundation found that meprobamate was particularly difficult to remove during the water-treatment process.

The other drugs found in the city's raw water supply were: carbamazepine, the anticonvulsant found in Tegretol; Dilantin, an antiepileptic drug; naproxen, the over-the-counter anti-inflammatory drug found in Aleve; and sulfamethoxazole, an antibiotic found along with another drug in Bactrim.

Those drugs were found in concentrations ranging from .62 parts per trillion to 1.9 parts per trillion, but none were found in the treated water.

Ms. Hunt said that Arlington submitted a request for a grant from the Awwa Research Foundation to study the removal of meprobamate from the water supply. She said it would probably focus on improving the plants' biofilters.

"Three years or four years ago, we couldn't have even measured this small of a quantity," Dr. Cluck said. "It's probably been there for a while, but nobody could measure in trillionths."