This unit begins by establishing context regarding the extent of the global drinking water challenge. Students build models of natural water systems, they investigate how these systems become contaminated, they explore how contamination can be prevented, and they examine how polluted waters can be purified. Laboratory methods for quantitatively measuring water quality are practiced. Students investigate the role and effectiveness of different natural and genetically modified organisms in cleaning up water polluted with crude oils. The physical, chemical, and biological technologies and processes utilized by waste water treatment plants are explored, including optional field trips to these facilities. To conclude this unit students apply their knowledge of water issues, water treatment technologies and the associated role of biological organisms, along with their engineering design experience to the challenge of designing a small-scale water treatment system for rapid deployment within natural disaster zones.