What is the relationship between materials and value, and how have they played into scientific practice and authority? This project unravels the long history of the use and value attributed to bodily substances in science and medicine. I use urine as an exemplary material for analyzing how shifting normative and marketable value shapes scientific work, its results, and their social implications. Fountain of Knowledge is composed of five case-studies dealing with global twentieth-century scientific and medical projects that centered on urine: as a reservoir in sex-endocrinology; as a technology in clinical medicine; as a self-consumed treatment; as an analytic in ethology; and as a resource in agriculture. Considered together, they offer new insights into the relation between material, value, and knowledge. They also reveal how changing our understanding and management of bodily substances could dramatically impact our relationship with the environment.