Risks associated with water can be significant in healthcare settings, from unexpected incidents of intrusion of water into occupied areas to microbial contamination of water supplies or equipment that uses water. As a result, water-related mitigation strategies are among the most challenging infection prevention and control issues involving the environment of care. This chapter addresses waterborne pathogens and water-associated infection risks in healthcare settings and strategies for infection prevention and control, including an overall approach to assessing risks and developing prevention strategies, such as facility/water system design, routine preventive maintenance for operations and equipment, and remediation measures during floods, hurricanes, or utility outages. Water disinfection/treatment options, including considerations for use and strengths and challenges of various modalities, are also discussed. The prevention and control of Legionella contamination of water distribution systems remains a significant concern in healthcare facilities. This chapter covers some of the risks associated with Legionella contamination but primarily focuses on water contamination with numerous other microorganisms, including waterborne bacteria and fungi, which can be present in the water distribution system and cause infections within the healthcare setting. See Chapter 86. Legionella pneumophila for further information on Legionella specifically. Additional guidance for water-risk mitigation measures is found in Chapter  118. Construction and Renovation.