Having a clean, reliable source of drinking water is essential for any community, but in many cases this is easier said than done. Engage young environmentalists in exploring the five factors affecting vulnerability of a groundwater supply with this simulation activity. Provided with the conditions of four hypothetical towns, students calculate a vulnerability score for each community's aquifer and answer questions about the results. This lesson allows learners to apply their knowledge of geology to better understand the availability of Earth's most valuable resource; fresh water.