In Tennessee, waterborne outbreaks were responsible for over 800 illnesses between June 2017 and August 2018. The Tennessee Department of Health utilized water testing to assess suspected water sources for pathogens during these investigations. Environmental health specialists collected water for testing from a variety of sources, including untreated well water, pool and hot tub water, and building water. Water testing results supplemented the epidemiologic, environmental, and clinical laboratory testing components of the investigations. Expanding capacity to include water sampling may improve future waterborne outbreak investigations.