Where there is weak state capacity to carry out regulatory, redistributional, and developmental functions characterizing much of the developing world, the role of governance and service delivery is also performed by a myriad of private actors. Institutional reform in the utility sector in developing countries has often failed to distinguish between social and economic regulation. I show how private actors like NGOs and local community groups undertake what I term “regulatory mobilization” to influence the new rules of the service delivery game, as well as to deliver much-needed basic services to urban poor communities. Based on extensive fieldwork carried out in the Philippines, this article reveals and explains the politics of the informal sector at the edge of the regulatory state. More than a decade since the privatization of the Metropolitan Waterworks and Sewerage System in Metro Manila in 1997, water access for the urban poor remained limited as privatized water utilities faced difficulties in extending service provision. In the context of an unpredictable regulatory landscape and an oligarchic patrimonial state, unexpected collective action by organized urban poor communities and NGOs has taken place around water as a subsistence right. Combining hybrid mobilizations to obtain water as well as influencing the rules governing their provision, these forms of regulatory mobilization appear to be peripheral and episodic. However, depending on how local and sectoral politics are conflated, such regulatory mobilization may sometimes not only result in obtaining subsistence goods, but may also occasionally project countervailing power in the policy sector, and influence formal regulatory frameworks in surprising ways.