Societies today face an array of global, water-related challenges with significant scientific dimensions and spanning the Food-Energy-Water-Nexus (FEW-Nexus). To prepare students to become tomorrow's global citizens, post-secondary learning experiences for undergraduate students must provide them with opportunities to learn and 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 at the University of Nebraska-Lincoln (UNL). Here, we report on discipline-based education research from the first iteration of the course focused on the scientific, social, economic, and policy dimensions of water, during which we engaged a diverse population of students (n=45) from a variety of majors, and backgrounds. Principles of effective undergraduate STEM instruction include: socio-hydrological systems, student engagement with authentic hydrological data, and computer-based models. We draw upon these constructs, data, and models to investigate (1) undergraduate students' science content knowledge, (2) reasoning about socio-hydrological issues, and (3) model-based reasoning and content retention. Findings illustrate growth in students' science content knowledge over the course of the semester, as well as important relationships between it and their model-based and socio-hydrological reasoning, all of which are core characteristics of the FEW-Nexus. Gain scores for pre/post assessments of students' content knowledge were predictive of their reasoning about a complex, real-world socio-hydrological issue. However, relationships between students' science content knowledge and model-based reasoning about water systems differed significantly across two projects involving computer-based simulations. We use these empirical findings to consider challenges and opportunities in the design of the course, particularly the integration of scientific and non-scientific dimensions of real-world socio-hydrological challenges.