An aquifer is a saturated, porous, permeable stratum or group of strata. Hydrogeological maps give a different view to standard geological maps, classifying the strata according to their importance as aquifers and dominant type of flow, through interconnected pore spaces or fractures. But geology, depositional environment, diagenesis and structure control aquifer properties and how the groundwater flows. Jane’s talk focusses on the Chalk, explaining how water flows and examining its properties, uses, responses to abstraction, vulnerability and contaminant movement.