A series of micro gravity investigations have been formulated to be performed in the current DECLIC and in the future DECLIC‐Evo on board the International Space Station, to provide a better understanding of fundamental processes that take place in water at near‐critical conditions. These investigations rely on the design heritage of an earlier fundamental physics study to explore the near‐critical behavior of pure water and for which the High Temperature Insert (HTI) was originally designed and built. They also have the overarching goal of providing some of the scientific underpinnings for future advances in supercritical water oxidation (SCWO) technologies (see Fig. 1).