Caffeine has created quite a quandary in the land of Starbucks. The drug has become so prevalent in the Seattle-area water supply that officials have had to change the way they track pollution.

Four years ago, King County water-quality experts began identifying sewer overflows and leaks in underground pipes based on traces of caffeine found in the water supply. The substance was ideal because the compound is not found in natural waters, according to chief county microbiologist Scott Mickelson. Caffeine remains intact through grinding, percolating, frothing--and human consumption and elimination.

But of the 216 water samples--some at depths of 640 feet--taken from Puget Sound last year, caffeine was detected in every one.

Mickelson attributes those findings to the area's booming population growth, noting that coffee typically enters the storm-sewer system when motorists, pedestrians and sidewalk vendors dump the last of their coffee into the street.

Researchers also discovered higher caffeine concentrations at certain times of the day. Caffeine readings jumped to eight times the normal level between 8:00 and 8:30 in the morning. "The joke was that everybody was getting rid of that first cup of coffee," says Mickelson.

Since the levels now preclude the use of caffeine as a tracer compound, researchers will instead use a nontoxic fluorescent dye to track pollution.