"The fact that a second contaminant in West Virginia's drinking water eluded detection for nearly two weeks — despite intense testing of the water — reveals an important truth about how companies test drinking water: In most cases, they only find the contaminants they're looking for." ...

Experts say it's not surprising that the drinking water company did not detect a second contaminant during its search for MCHM. Laboratories can hunt for unexpected chemicals, but generally they don't. ...

There are tens of thousands of chemicals in use.

"To expect a water company to monitor for thousands of chemicals, it just is not practical and it would be cost-prohibitive," added [Brent] Fewell, whose company works with more than 100 drinking water systems."

Elizabeth Shogren reports for NPR's Morning Edition January 24, 2014. [2]