Nanoscale science and technology play central roles in our understanding of how Earth works and in the environmental science field of study. As a freshwater source, groundwater is second in abundance only to water found in glaciers and polar ice. Groundwater is critically important as a freshwater source to much of the Earth’s population; however, when it is polluted, it becomes a severe and dangerous liability with hundreds of millions of lives at stake from waterborne illnesses. This chapter provides teachers with critical background information on the nature of groundwater and the reasons why nanoscale science and technology are so relevant to groundwater pollution.