In this final lesson, students use the knowledge they have accumulated throughout the module to complete the Water for All Challenge. The teams design and build desaladoras—desalination devices that use passive solar energy. Students contend with scarcity as they learn that their desaladoras must fall within budget constraints. They apply the engineering design process (EDP) to building a device that incorporates the principles they learned and observed while improving on the design. Each team also creates a public service announcement (PSA) for its desaladora targeted at the country the team chose. Finally, students participate in a Water Conservation Expo in which they display their devices and present their PSAs along with the information they gathered about their team’s country. We recommend reading Chapter 3, which is included in this book selection and provides a module overview and summary. A materials list, safety notes, standards, teacher background information, assessment, and Internet resources are provided. This book selection also includes the Table of Contents, About the Editors and Authors, Appendix, and Index.