Societies today face an array of water-related challenges within the Food-Energy-Water-Nexus (FEW-Nexus). To prepare students to become tomorrow's global citizens, postsecondary learning experiences must support them to learn reason about socio-hydrological issues such as agricultural water use, water quality, and water security. However, undergraduate courses designed to cultivate water literacy are few and far between. To begin to address this need, we are engaged in a 3-year, NSF-funded project focused on the iterative design, implementation, and study of a new, introductory (100-level), interdisciplinary course - Water in Society – at the University of Nebraska-Lincoln (UNL). Here, we report on the discipline-based education research in which we are engaged around the first iteration of the course, during which we served a diverse population of students (n=45) from a variety of majors (STEM and non-STEM) and backgrounds. The course is grounded in a set of instructional design heuristics that foreground principles of effective undergraduate STEM instruction and contemporary learning theory, socio-hydrological systems as a core construct for the course, and student engagement with authentic hydrological data and computer-based models and simulations. We utilize design-based research methods to engage in iterative development and refinement of the new course, drawing upon data collected during the course that includes student artifacts, interviews, and pre-/post-course assessments, to investigate students' science content knowledge, beliefs, and reasoning about socio-hydrological issues, as well as their model-based reasoning and systems thinking, all of which are core characteristics of the FEW-Nexus. Findings illustrate growth in student outcomes over the semester, as well as key interactions between conceptual understanding and socio-hydrological systems thinking. We use these empirical findings to illustrate and discuss challenges and opportunities we have experienced as an interdisciplinary team engaged in undergraduate education in the FEW-Nexus, as well future directions for the course.