Careful planning and management of our water resources is critical to ensuring supplies of clean water at a reasonable cost in the future. Illinois lies adjacent to one of the world's largest bodies of fresh water, Lake Michigan, and has seemingly endless groundwater and surface water. However, parts of Illinois face the same dilemma as states in the west and southwest -- projected water shortages by the year 2020 because of ever-increasing demands for water, combined with legal and physical constraints. The amount or quantity of water that exists in Illinois depends on four factors: water availability, water demand, the supply from existing delivery systems and actual use. While water availability is generally more than adequate to meet future demand, growth in population, the economy and in energy consumption are leading to projected water shortages in some areas. This policy brief advocates for protection of Illinois' water supply through sustainable development practices combined with improved water planning and increased public awareness. It describes current water demands in Illinois and the sources of water supply. It also outlines the considerable challenges to meeting current and future demands, as well as actions to ensure adequate water availability in both quantity and quality for future generations.