The global demand for energy and water is projected to increase by 40% and 55%, respectively, by 2050. Meeting these targets in an efficient, affordable, and sustainable manner necessitates significant scientific and technological advances. The inherent challenge lies in the complexity of water-energy systems due to interactions that span multiple length- and timescales, and this is where leveraging advances in materials provides an opportunity to make them more efficient. This talk will focus on functional materials that are thermally responsive – ranging from ionic liquids to inorganic salt hydrates, and semiconducting polymers – to enable low energy chemical separations (clean water) and to decarbonize heat (clean energy). Ionic liquids combine high ionic strength and affinity for water owing to hydrophilic functional groups, while hydrophobic moieties impart a critical temperature above which these materials release water. The novelty of these materials is that the enthalpy of separation is approximately three orders of magnitude lower than conventional liquid-vapor thermal separations that vaporize water, and the critical temperature can be achieve using solar energy. Another set of materials that are thermally responsive are salt hydrates that can undergo reversible thermochemical reactions to store and release energy in the form of heat. To mitigate stability challenges associated with volumetric changes accompanying the thermochemical reaction, an inorganic-organic composite material is designed by encapsulating the salt into a hydrogel matrix. The novelty of the approach is that it creates a highly porous matrix around the particles to achieve a form-stable composite for a highly reversible thermal battery unlike conventional approaches of impregnating the salt into a porous matrix. The last class of materials that will be highlighted are semiconducting polymers for direct conversion of heat into electricity via the thermoelectric effect. The flexible nature of the polymer and the use of solution-processing techniques opens new avenues for wearable electronics that harvest body heat or provide personal cooling to lower energy demands. These examples demonstrate the potential of dynamic and responsive materials to modulate heat and mass transport for the next generation energy and water systems.