There is no primary drinking water standard for methyl tertiary- butyl ether (MTBE). In 1997, EPA published an Advisory document on methyl tertiary-butyl ether (Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Methyl Tertiary-Butyl Ether, Environmental Protection Agency Office of Water, 1997). This non-regulatory document recommends keeping levels at a range of 20 to 40 parts per billion (ppb) or below. At this level, MTBE will probably not generate an odor or taste problem and there is little likelihood that in this range negative resulting health effects will occur.
Additional information on MTBE is available at http://www.epa.gov/dwucmr/first-unregulated-contaminant-monitoring-rule.