This course provides an introduction to water in the subsurface environment. The emphasis is on the common unifying concepts that underlie the two main topics covered - groundwater and geothermal systems - and the linkages and differences between them. In addition to the concepts, the students will learn how to observe, measure and/or estimate key parameters, e.g. flow through porous and fractured media, interaction with surface water/springs, and the effects on these parameters from human exploitation (pumping and production). For geothermal systems, this will encompass the liquid and gas phases of water and how surface measurements can provide insights into the deep reservoir. Learning concepts, processes and parameters in groundwater and geothermal systems will be contextualised by the global significance of water and renewable energy resources, and how these are valued and managed in Aotearoa (including matauranga and kaitiakitanga perspectives) and the Pacific.