The many headlines focusing on 'land grabbing' have distracted attention from the role that access to water plays in underpinning the projected productivity of foreign direct investment in acquisition of agricultural land in developing countries. This paper identifies questions that arise about the explicit and implicit water requirements for irrigation in agricultural projects on land that is subject to such foreign investment deals. It focuses particularly on land acquisition in sub-Saharan Africa (SSA), where, for savanna ecosystems that cover some two thirds of the region, rainfall uncertainty is the principal constraint to increased agricultural productivity. The paper argues that, even where land acquisition deals do not specify irrigation, choice of location and/or crop type indicates this is invariably an implicit requirement of projects. It is arguable that private investment in water infrastructure (e.g. for water storage) could provide wider benefits to neighbouring small-scale producers, thus reducing the risk inherent in much of African agriculture. However, it is also possible that foreign investment may compete with existing water use, and some land deals have included provisions for priority access to water in cases of scarcity. Empirical studies are used to identify the mechanisms through which large-scale land investments influence water availability for smaller-scale land users. The paper concludes that, although effects on water resources may constitute one of the main impacts of land deals, this is likely to be obscured by the lack of transparency over water requirements of agricultural projects and the invisibility of much existing local agricultural water management to government planning agencies.