Yes, for each contaminant, when EPA sets the MCLG, it is based on the assumption that a person could consume two liters of drinking water containing the maximum level of the contaminant daily for 70 years without experiencing any known health effects. The MCLG is a non-enforceable health-based goal. For known carcinogens, or cancer-causing agents, the goal is set at zero, assuming that any level of consumption could present a cancer risk.
MCLs, which are the legal limit, are set as close to the goal as possible, while taking into account technical and financial barriers that may exist. Additional information can be found at http://water.epa.gov/lawsregs/rulesregs/sdwa/currentregulations.cfm.