Environmental health literacy (EHL) is developing as a framework that can inform educational interventions designed to facilitate individual and collective action to protect health, yet EHL measurement poses several challenges. While some studies have measured environmental health knowledge resulting from interventions, few have incorporated skills and self-efficacy. In this study, a process-focused EHL instrument was developed, using the Newest Vital Sign (NVS) health literacy instrument as a model and tailoring it for the context of private well contamination with toxic metals. Forty-seven (47) participants, including undergraduate students and residents of communities with contaminated well water, piloted a prototype EHL instrument alongside NVS. Results suggested a moderate degree of correlation between NVS and the EHL prototype, and significant differences in scores were observed between students and residents. Responses to a self-efficacy survey, tailored for drinking water contaminated with arsenic, revealed significant differences between students and residents on items related to cost and distance. In response to open-ended questions, participants identified a range of potential environmental contaminants in drinking water and deemed varied information sources as reliable. This study highlights differences in knowledge and self-efficacy among students and residents and raises questions about the adequacy of EHL assessments that mimic formal education approaches.