This morning the Associated Press released the first of its three-part investigation into U.S. water quality. Among the national findings: Minneapolis drinking water contains caffeine.

This is no doubt pleasurable to Minneapolis' legion of coffeeholics and Red Bull fans, who might hope to sate their addictions from the tap for free. However, AP's report is a potential gut punch not only to lovers of unadulterated agua but to Minneapolis Mayor R.T. Rybak.

Rybak has rather loudly campaigned against bottled water, arguing that municipal supplies are at least as safe and don't add plastic to the waste stream. Minneapolis citizens have more than their lips on the line: Taxpayers spent $56 million on an upgraded "ultrafiltration" plant in Columbia Heights that opened in 2005.

So how caffeinated is water in the Mill City? The AP report doesn't say. A call to the story's investigators circled back to the U.S. Geological Survey (USGS), which studied Minneapolis' drinking water in this 2000-2002 report (PDF). (The AP didn't do its own testing, but relied on existing research.) Pam Shubat, the Minnesota Department of Health's risk assessment supervisor, said she was also told the story relied on the USGS publication.

If so, let's throw in a rather large caveat: Local USGS Supervisory Hydrologist Jim Stark says his agency's data came entirely from the old treatment plant, years before the modernized ultrafiltration plant came online.

But still — how much caffeine was in the water then? Health Department spokesperson Stew Thornley said Minneapolis officials told him that the caffeine concentrations were .02 to .04 parts per billion. That's approximately 100 million times less than the caffeine in a cup of coffee, Shubat says. "It's nothing in comparison," she adds. "It's not even worth discussing. This isn't the point."

The point is this: Advanced technology lets analysts detect incredibly small amounts of a substance, so they use caffeine as a marker of wastewater's contamination of drinking water. In this case, it's simply not a case of human health risk.

To be sure, on the other side of the intake pipes — in the watershed — human byproducts can and do pose environmental risks. In water sources feeding Minneapolis, the AP and USGS cite the presence of acetaminophen (Tylenol), caffeine and cotinine (a nicotine byproduct), among other chemicals. The bottom line: If you want to feel all jittery about something, focus on the water outside your house.