美国环境保护局（USEPA）正在考虑降低砷的最大污染水平（MCL），目前为0.05 mg/L（50 ug/L）至0.5-20 ug/L。拟议的国家初级饮用水砷法规预计将于1995年11月出台。鉴于这一拟议的新砷标准，南加州大都会水区（Metropolitan Water District of Southern California，大都会）进行了一项全国性调查，以帮助评估更严格的砷监管对供水社区的影响，并提供较低的砷排放标准- 用于监管输入的砷含量信息。这项调查针对的是美国10个美国环保局地区人口至少为5万的公用事业公司。该调查旨在确定未经处理和处理的地表水和地下水中的砷含量。调查结果表明，与中西部、西南部和西海岸地区高得多的砷暴露水平相比，东海岸的砷暴露水平高于2 ug/L的人群极低。砷含量在密西西比河以西增加，在加利福尼亚州、犹他州、新墨西哥州、内华达州和亚利桑那州等州变得更加突出。 处理后的水砷含量平均为1.3 ug/L（平均值为0.6 ug/L），范围为<0.5至38.6 ug/L，地下水供应中的砷含量较高。调查结果表明，约23%的调查人群暴露在高于2微克/升的砷水平下，且绝大多数较高浓度的砷在美国西部。

The United States Environmental Protection Agency (USEPA) is considering lowering the maximum contaminant level (MCL) for arsenic, which is currently 0.05 mg/L (50 ug/L) to 0.5-20 ug/L. The proposed National Primary Drinking Water Regulation for arsenic is expected in November 1995. In anticipation of this proposed new arsenic standard, the Metropolitan Water District of Southern California (Metropolitan) conducted a nationwide survey to help assess the impacts of a more stringent arsenic regulation on the water supply community and provide low-level arsenic occurrence information for regulatory input. The survey was aimed at utilities in the US with populations of at least 50,000, representing all 10 USEPA regions. The survey was conducted to establish both untreated- and treated-water arsenic levels in surface and groundwater. The survey results indicate that population exposure to arsenic levels of greater than 2 ug/L is extremely low on the East Coast, as compared to much higher exposures in the Midwest, Southwest, and West Coast areas. Arsenic levels increased west of the Mississippi River and became more prominent in states such as California, Utah, New Mexico, Nevada, and Arizona. Treated water arsenic levels averaged 1.3 ug/L (mean value--0.6 ug/L) and ranged from <0.5 to 38.6 ug/L, with higher levels in groundwater supplies. The survey results indicated that approximately 23 percent of the survey population is exposed to arsenic levels greater than 2 ug/L, and the vast majority of higher concentrations is in the western US.