This article introduces the special issue on 'Estimated Truths' which investigates the role of estimation in knowledge-making about water and, through it, contributes to thinking place as environment in the historical geography and history of knowledge. It argues that while historical geographers and historians of science have paid much attention to precision and quantification, approximation and estimation have also played an important role in knowledge-making and deserve more attention. It

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... cusses the roles played by uncertainty and estimation in the water sciences and makes the case for more sustained engagement with the influence of the environment e understood as a dynamic set of human and nonhuman actors and forces e on knowledge-making. Finally, the article presents the five papers and discusses their individual and collective contributions to the themes of the special issue and to further investigation into the making and operation of estimated truths.