Water resource managers often tout the potential of potable water reuse to provide a reliable, local source of drinking water in water-scarce regions. Despite data documenting the ability of advanced treatment technologies to treat municipal wastewater effluent to meet existing drinking water quality standards, many utilities face skepticism from the public about potable water reuse. Prior research on this topic has mainly focused on marketing strategies for garnering public acceptance of the process. This study takes a broader perspective on the adoption of potable water reuse based on concepts of societal legitimacy, which is the generalized perception or assumption that a technology is desirable or appropriate within its social context. To assess why some potable reuse projects were successfully implemented while others faced fierce public opposition, we performed a series of 20 expert interviews and reviewed in-depth case studies from potable reuse projects in California. Results show that proponents of a legitimated potable water reuse project in Orange County, California engaged in a portfolio of strategies that addressed three main dimensions of legitimacy. In contrast, other proposed projects that faced extensive public opposition relied on a smaller set of legitimation strategies that focused near-exclusively on the development of robust water treatment technology. Widespread legitimation of potable water reuse projects, including direct potable water reuse, may require the establishment of a portfolio of standards, procedures, and possibly new institutions.