When modern science first began to coalesce in the 19th century, its first global superstar, Alexander von Humboldt, described the arduous task of collecting accurate data to obtain verifiable explanations for natural phenomena as “apprehending the apparition.” Doctors, engineers and scientists across the globe made key discoveries that together laid the foundation for today’s field of hydrogeology and made the task of understanding groundwater possible. Find out about Darcy’s law, cholera in London, and just how much of the world’s available freshwater is actually groundwater. (The answer will surprise you!)