This paper presents a general approach to rainwater as a water resource. The use of rainwater, a common practice in many civilizations of the past throughout the planet, is regaining prominence in both developed and developing countries. In the latter and especially in some rural areas of Asia, Africa and Latin America, rainwater may provide more abundant and better-quality water than distant and polluted surface or groundwater sources. In developed countries, the use of rainwater diminishes pressures on public networks, satisfying certain uses without having to resort to very expensive and environmentally problematic infrastructures. However, rainwater suffers from a major problem which is the uncertainty of supply, especially in the absence of wellsized catchment surfaces and storage tanks for areas of scarce and erratic rainfall. In hydrosocial terms, the use of rainwater can empower commuThe objective of this article is highlighting the importance of the hydrosocial strategies and practices implemented in the 30 missionary towns founded between the XVII and XVIII centuries in the Vice Royalty of the Rio de la Plata by the Society of Jesus, a Catholic religious order, among the region’s Tupi-Guarani indigenous communities. It aims to contribute towards rescuing and valuing the historical practices of collection and use of river and rainwater by Jesuit- Guarani communities, practices that remain alive in the region’s cultural geography and social memory. The work is grounded on the analysis and interpretation of cultural responses to water-related issues, the historical precedents of such strategies, practices and knowledge, and the recognition of their value through historiographical research. It seeks to provide elements for the study of hydro-social cultures reflecting on past processes and the production of knowledges associated to water cultures in the Guarani region of South America.