氡是一种天然放射性气体。1986年《安全饮用水法》修正案要求美国环境保护局（USEPA）监管饮用水中的氡。1991年7月18日公布了300 pCi/L水的拟议最高污染物水平（MCL）。自从美国环保局最近提议对水进行监管以来，有关水的监管一直在继续。本文探讨了美国环境保护局拟议规则中的关键问题。包括35个参考文献、表格和图表。

Radon is a naturally occurring radioactive gas. The US Environmental Protection Agency (USEPA) was required by the 1986 Safe Drinking Water Act amendments to regulate radon in drinking water. A proposed maximum contaminant level (MCL) of 300 pCi/Lwater was published July 18, 1991. Since then, regulation of radon in drinking water has been the subject of continuing debate, congressional action, and, more recently, USEPA efforts to craft a proposed regulation. This article examines key issues in anticipation of USEPA's proposed rule. Includes 35 references, tables, figure.