Aquifers are typically saturated regions of the subsurface that produce an economically feasible quantity of water to a well or spring (eg: sand and gravel or fractured bedrock often make good aquifer materials). Most land areas on Earth have some form of aquifer underlying them, sometimes at significant depths. In this book, the authors present current research in the study of the types, impacts and conservation of aquifers. Topics discussed include the effect of aquifer heterogeneity; hydrochemical features of groundwater from aquifer systems occurring in Sao Paulo, Brazil; aquifer system characterisation using integrated geophysical methods; pollution risk of groundwater in a semi-arid region by wastewater rejections; a numerical study of aquifer thermal energy storage systems influenced by regional groundwater flow and fluid flow and contaminant propagation in fractured rock aquifers.