Osmosis represents a particularly harsh constraints for most forms of life and requires organisms to tightly regulate water flows. For example, the kidney system of land animals actively pumps ions to reabsorb water and avoid desiccation. On the other side of the spectrum, fresh water organisms face a constant osmotic fluid intake and must excrete water to compensate. Yet, in the absence of active molecular water transporters, the physical mechanisms behind active water effluxes remain unclear, as well as the associated energetic cost. The goal of this internship and PhD project is to compare strategies of osmoregulation from the perspective of thermodynamics and theoretical biophysics. Models will describe the nanofluidic transport of ions and water through molecular transporters, and include them in effective models of osmoregulation at the cell or tissue level. One long-term aim of this project is to understand how embryos that develop in freshwater achieve osmoregulation without any (known) specific organ dedicated to the task. This latter part of the project will be done in collaboration with experimental biologists.