Big Data is increasingly seen as important in studying the city. This pertains to both its methodological capacity and the societal implications it may have. In this article we draw on contemporary literature to discuss the potentials and challenges of Big Data for addressing pressing urban issues. In addition, we examine the potential of Big Data as a methodological tool for two Caribbean cities, Paramaribo and Port of Spain, for developing new knowledge on urban issues that matter in such cities, specifically water-related risks and security. We do so by interrogating Twitter data to uncover relevant geographical and social patterns of tweets pertaining to water-related risks (Paramaribo) and security/crime issues (Port of Spain) and confronting these with qualitative knowledge about these places. We argue that Big Data are a powerful resource for discovering interesting patterns, but one needs to be critical of the methodological caveats and consider the social-cultural specificities of ICT use.