This talk will present some of our recent work on advanced materials and systems at the energy and water nexus, including thermoelectric and thermogalvanic materials and systems for direct conversion of heat into electricity, high thermal conductivity semiconductors and polymers, optically opaque and infrared transparent fabrics, clean water technologies, and grid level energy storage systems. Thermoelectric materials have seen significant improvements over last two decades, but innovations are needed to develop their applications since their heat-to-electricity conversion efficiencies are still limited. In addition, electrochemical systems such as batteries can also be used to convert heat into electricity, which could be especially attractive for low temperature waste heat recovery. Although thermoelectric energy conversion calls for low thermal conductivity materials, many other applications require high thermal conductivity materials. We are developing materials with high thermal conductivity ranging from semiconductors to polymers, including BAs which has second highest thermal conductivity behind diamond. As another example, we show that polymers can be made as thermally conductive as metals by aligning molecular orientations despite that they start with low thermal conductivity. After these examples, we turn attention to energy and water technologies based on engineering thermal radiation. With properly chosen polymer fiber diameters, we design fabrics so that they are opaque to visible light and yet allow thermal radiation from human body to escape to environment for passively cooling of human body. We also demonstrate the ability of boiling water and even creating super-heated steam under unconcentrated sunlight. The talk will conclude with a discussion of a novel approach to grid level energy storage.