Groundwater levels can tell us about how water moves in the ground. By studying these levels in Kaohsiung City, Taiwan, researchers found different types of aquifers based on how water levels change over time. They used a method called Hierarchical Clustering Analysis to group wells with similar patterns. The clusters matched the types of rocks underground and how old they are. This helps us understand how water moves in the ground and how to manage it better, like saving money on drilling for water.