Public water systems in Connecticut, Maine, Maryland, New Hampshire, New Jersey, and Rhode Island sampled treated drinking water from 1993-2006 and analyzed the samples for methyl tert-butyl ether (MTBE).  The U.S. Geological Survey examined trends in the occurrence of MTBE in drinking water derived from ground water in these States for two near-decadal time steps; 1993-1999 and 2000-2006.

MTBE was detected in 14% of drinking water samples collected in all States from 1993-1999 and in 19% of drinking water samples collected from the same systems from 2000-2006 and this difference is statistically significant.  However, a significant increase in the occurrence of MTBE for these two time steps was observed in only three individual States: Maryland, New Jersey, and Rhode Island.  Trends in the occurrence of MTBE in each State by individual year indicated significant positive trends in Maryland and New Hampshire. 

The 95^th percentile of concentrations of MTBE in drinking water from each State was generally less than 3 micrograms per liter (mg/L) for each time step.  Less than 1 percent of drinking-water samples in all States for each time step had concentrations greater than 20 mg/L, the lower limit of the US Environmental Protection Agency drinking-water standard.  Significant, increasing trends in MTBE concentrations were observed in Maryland and Rhode Island by individual year.

Water that is contaminated by MTBE is increasingly being captured by public water supplies in the Northeast and transmitted to consumers, although most concentrations are considerably less than those that might cause taste and odor concerns.  Future trends in the occurrence of MTBE in public water systems are uncertain; however, decreased usage of MTBE in this area, as a result of the Energy Policy Act of 2005, will likely result in lower occurrence of MTBE.