The Associated Press on Monday released the results of a five-month investigation that is focusing new attention on issue of pharmaceuticals in the nation's water supplies. According to AP, trace amounts of medications have turned up in the drinking water supplies of at least 41 million Americans.

"It's almost hard to describe the concentrations we're talking about here," Davis said. "If the detection threshold was a part per billion, none of these pharmaceuticals that AP is talking about would have shown up at all."

He said the recent surge in research -- and media interest -- about pharmaceuticals in water can be traced to the development of new devices able to detect compounds at ever-smaller concentrations.

One part per billion is the equivalent of a single drop of water in an Olympic-sized swimming pool. Scientists can now measure certain compounds in concentrations 1 million times smaller than that, clear down to the level of parts per quadrillion.

In other words, there is no such thing as zero anymore, even if that is the number water customers would prefer to see, Davis said. "Unfortunately, the world works on a scale where present equals bad and absent equals good."

At present, most water utilities do not test for pharmaceuticals because it is expensive, difficult, and safe drinking water standards do not require it. To detect drug compounds at the vanishingly small concentrations found in the valley's water requires several hundred thousand dollars' worth of laboratory equipment, Davis said.

"This isn't like looking through a microscope. There aren't a dozen labs in this country that can do this work," he said. "The reason we're doing it is because we're leading the research for the water industry nationwide."

Davis acknowledged that considerably more research is needed before scientists can speak unequivocally about the potential effects of long-term exposure to extremely low amounts of pharmaceuticals.

The three drugs found in local drinking water are the anti-anxiety drug meprobamate, the anti-convulsant drug carbamazepine and the anti-epileptic drug phenytoin, commonly known as Dilantin.

Meprobamate shows up at 6.1 parts per trillion, carbamazepine at 0.5 parts per trillion and phenytoin at 1.6 parts per trillion. To get a concept of that amount, Davis said, compare that drop of water from before to about a thousand Olympic-sized swimming pools.

Recent tests have identified traces of six other medications in untreated water taken from Lake Mead: cholesterol drug gemfibrozil; antibiotics sulfamethoxazone and trimethoprim; beta blocker atenolol; anti-inflammatory diclofenac; and pain reliever naproxen.

Sulfamethoxazone was found in concentrations of 18 parts per trillion. The rest of the drugs showed up at less than 3 parts per trillion.

The Las Vegas Valley gets about 90 percent of its drinking water supply from Lake Mead. That's also where the valley dumps nearly all of its treated waste water, which flows down the Las Vegas Wash and into the reservoir upstream from the water authority's intake pipes.

All Lake Mead water undergoes ozonation, one of the most intensive treatment methods on the market, before being delivered to valley residents.

Davis said some further treatment method might not eliminate the lingering traces of pharmaceuticals but merely reduce them to levels too small to be detected by current technology.

It becomes a question of diminishing returns.

"If the bigger number isn't a health concern, why go to the trouble and expense to reduce it to the smaller number?" Davis said. "It's not a function of laziness. It's a function of limited resources."

Contact reporter Henry Brean at hbrean@reviewjournal.com or (702) 383-0350.