The success of water conservation restrictions depends in part on governments' capacity to monitor water use. Inviting the general public to report instances of water waste is a potential means of expanding capacity to monitor and enforce water use. Does the general public engage in such "participatory surveillance?" How does participation in public monitoring vary across communities? Is participatory surveillance associated with the achievement of water conservation goals?This study explores the contextual correlates and implications of public responses to participatory surveillance as part of a regime of water restrictions adopted in response to a drought emergency. Our empirical subject is water conservation in California communities during that state's 2014-2017 drought. In response to a severe water shortage, California's governor ordered utilities to reduce potable water consumption and introduced a series of statewide measures to promote conservation. For instance, California authorities prohibited washing down driveways and sidewalks, outdoor irrigation that causes excess runoff, using a hose to wash a motor vehicle (unless the hose is fitted with a shut-off nozzle), and using potable water in a fountain or decorative water feature, unless the water is recirculated. As part of these efforts, state and local agencies established telephone hotlines and websites for the public to report water waste and violations of drought restrictions anonymously. After a complaint was made, utilities proceeded with a series of escalating enforcement steps, including informal education, formal warning, and monetary penalties. That is, the governments actively invited the public to participate in surveillance of their neighbors as a means of promoting water conservation. The people responded with gusto: over the course of the drought emergency (August 2014 to April 2017), Californians reported more than 485,000 water waste complaints. The California communities provide an extraordinary opportunity to explore participatory surveillance as a means of managing a drought emergency.To that end, we analyze monthly water waste reporting and conservation across 408 water utilities in California during the drought emergency. To preview our results, we find that besides characteristics of water