Although clean, potable groundwater constitutes one of our most valuable resources, few students or science educators hold complete and appropriate understandings regarding the concept. Recent studies that focus on secondary students' and preservice science teachers' understandings of groundwater found little difference between the groups' conceptualizations of subsurface hydrology. This article discusses possible reasons for the apparent lack of appropriate understanding regarding the complex concept of groundwater. Specifically, we concentrate on the lack of emphasis concerning groundwater content in standards documents, the need for increased attention to students' spatial reasoning abilities, inadequate formal instruction for science teachers concerning groundwater, and difficulty in designing appropriate assessment of groundwater concepts. We conclude by offering suggestions for enhancing the teaching and learning of groundwater.