Tiny amounts of pharmaceuticals and personal care products detected in the drinking water of the nation's biggest city continue to pose no public health risks to residents, environmental officials said Friday.

The city's Department of Environmental Protection drew samples from three upstate watersheds between March and December last year and analyzed them for 72 compounds, including antibiotics and prescription medications.

The DEP said that the tests detected 14 pharmaceutical and personal care products at least once but that none was found at levels that would pose a risk to the city's nearly 9 million residents. It said caffeine, the pain relievers acetaminophen and ibuprofen and the seizure-controlling medication carbamazepine were among the compounds that were detected.

"For most of these detected compounds, a person would have to drink at least tens of thousands of glasses of water a day to get one effective dose of the substance or to meet a toxicity threshold," the DEP said in a statement.

The study follows one done in 2009 that also detected tiny amounts of pharmaceuticals and personal care products, including penicillin and the insect repellent DEET, in the city's drinking water.

The initial study was prompted in part by an Associated Press investigation that found pharmaceuticals in drinking water of dozens of the country's major water providers, serving 41 million people.

Human health risks from trace pharmaceuticals are unclear, and the federal government does not regulate their levels in drinking water.

The DEP said it monitors about 250 contaminants in the city's water.