There is a growing need for public understanding about groundwater resources. Knowing what groundwater and aquifers are is fundamental to understanding more complex issues such as groundwater quality and availability. However, groundwater and related concepts are among the topics that instructors most struggle to teach. Although constructivist theories suggest that students' preconceptions or misconceptions can be used as teaching tools, the question about exactly how remains. A resource perspective on this question states the first step involves understanding students' preconceptions. To gain a deeper understanding of college students' pre-instructional mental models about groundwater residence, 215 students enrolled in introductory-level environmental geoscience courses taught at two large US state universities were surveyed. An open-ended questionnaire asked participants to draw and label a concept sketch. Follow-up interviews asked participants to elaborate upon their concept sketches. Eight categories of mental models emerged from the analysis of the collected data. These results were interpreted through the lens of cognitive schema theory, which generated to four patterns of mental models. These patterns emphasize key aspects of students' pre-instructional mental models about groundwater residence. Instructors can use this information to design instructional activities about groundwater and aquifers using a resource perspective.