text: EPA first listed MTBE in 1998 as a candidate for development of a national Maximum Contaminant Level (MCL) standard in drinking water. As of 2020 the agency has not announced whether it will develop an MCL. EPA uses toxicity data in developing MCLs for public water systems.
  California established a state-level MCL for MTBE, 13 micrograms per liter, in 2000.