The co-production of public services by users and professionals has been the subject of much discussion. By contrast, we know little about how users engage in the regulation of co-produced services, a process we call co-regulation. Relying on the concept of civil regulation, our qualitative case study analysis of the Grenoble water services reveals three activities at play in co-regulation: information processing, standard-setting and modifying behaviours. Moreover, we highlight boundary conditions for co-regulation to be effective and contribute to value co-creation, namely an active civil society and strong relationships with local decision-makers.