Within the past three decades, more than 2.6 billion people have gained access to an improved water source and 2.1 billion have gained access to an improved sanitation facility. However, improved does not always mean people have safe, reliable, accessible, or equitable water and sanitation services. Waterborne diseases continue to cause and estimated 500,000 deaths each year. What causes waterborne diseases, and what is the role of engineered systems in their spread or prevention? How can we evaluate interventions to improve health and well-being? How can research address these challenges?