As in many large cities, the now prevailing technical model for producing and distributing water in La Paz and El Alto is that of a centralized network serving the whole population of the two cities. La Paz and El Alto are no exception to the reality of the major cities of the Global South, where the technical service offer is struggling to keep pace with the rate of urban growth, which above all raises technical challenges (availability of water resources, the operator's capacity to extend the networks and socioeconomic challenges (the low contributory capacity of the inhabitants of the peripheral zones). However, the network managed by the main operator is not the only way these metropolitan areas access water. Many families obtain their water from networks belonging to small cooperatives, the "small systems" that supplement the "big system" of the centralized network. This paper opens up discussion on the governance and regulation of water services by integrating the insightful thinking of E. Ostrom on the interlocking of the different levels of rules, mainly the "operational" rules with the "collective-choice arrangements" with the higher level of "constitutional rules". The two cases presented in this paper typify the thinking on the way that the dynamics of the commons and public service are interlinked: one involves the environmental risks and possible trade-offs required to balance the interests of rural (upstream) communities and the general interest (urban water); the other one shows how urban water cooperatives have gradually come to fill the gaps left vacant by the public service, driven by communities who have found the means of organizing and producing the service on their own and defining the rules for its operation and sharing, their sustainability is now called into question at the economic, social and environmental level. Observation of what these commons reveal about the social actors' expectations and possibilities for action in the area of access to drinking water is a precious entry point to renew thinking on the governance and regulation of services at the global scale of the agglomeration, while unquestionably helping further the sector-based discussions.