Sustainable Development Goals are full of synergies but also trade-offs, especially when it comes to food and water. Irrigation is often promoted to boost production and nutrition, yet its local impacts depend on who benefits and how scarce water is.  We first use large-scale land acquisitions as a natural experiment: analyzing over 400 land deals, we find that while production increases, water scarcity worsens and diets in local communities actually often declineas land shifts to export crops. Expanding the analysis to the global scale, we show that irrigation generally improves diets, but the benefits are strongest under water stress. This reveals a counterintuitive and previously undocumented trade-off between food and water security. Returning to the natural experiment to probe mechanisms, we find that nutrition outcomes vary sharply across types of land deals: some raise incomes and improve diets, while others reduce access to micronutrients. These patterns are consistent with a dynamic in which irrigation investments by export-oriented agribusiness predominantly target water-secure land, effectively crowding out locally consumed crops. Together, these findings highlight the need for policies that pair irrigation with nutrition-sensitive incentives and stronger protection of water rights. In this context, I will briefly outline our ongoing efforts within a UN FAO initiative to characterize and safeguard water tenure, a critical but often overlooked foundation of equitable and sustainable water governance. I will close by giving a short overview of current and future work at the Human and Environmental Systems (HUES) group at Eawag and opportunties for collaboration.