Healthy forests act as natural infrastructure by filtering water and buffering against the impacts of floods and droughts. Although these benefits are widely known, they have rarely been presented in a way that is actionable for decision-makers – such as utilities, water agencies, and companies – to prioritize investing in natural infrastructure for water. This report evaluates the potential role that forest restoration can play in the Cantareira Water Supply System, São Paulo's primary water source, using a replicable approach so that similar research can be done in different geographies. The study finds that restoring 4,000 hectares of native forest in the Cantareira can reduce soil erosion by roughly 36 percent, reducing sediment management costs to yield a 28 percent return on investment for the water company. In addition, restoration of this scale would increase dry season water flow and may even increase annual water supply. The report makes this research actionable by supplying recommendations for program design to facilitate investment in natural infrastructure in São Paulo. [2]