Healthcare facilities (HCFs) in low- and middle-income countries frequently lack water, sanitation and hygiene (WASH) services that are adequate to implement infection prevention and control (IPC) practices, decrease healthcare-associated infections and antimicrobial resistance, and provide quality healthcare. The Water and Sanitation for Health Facility Improvement Tool (WASH FIT), initially published in 2017 and updated in 2018, is a risk-based, continuous improvement framework. The tool aims to improve WASH and related facility management and may contribute to quality of care (QoC) efforts. To date, there is no guidance available on how to monitor and evaluate the use of this tool nor is there rigorous evidence on its effectiveness. We developed a conceptual WASH FIT evaluation framework by drawing from the broader WASH, health systems strengthening, and QoC evidence base. This framework provides a common basis to plan, implement, monitor, and evaluate potential inputs, outputs, outcomes, and impacts from applying WASH FIT. Routine use of the tool, coupled with WASH infrastructure improvements as guided by the tool, can lead to better IPC practices, and may support improvements in occupational safety, QoC, global health security, and ultimately progress towards achieving Sustainable Development Goals 3 (good health and well-being) and 6 (clean water and sanitation).