This research investigated the issues associated with integrating ultraviolet (UV) disinfection into water treatment plants (WTPs). These issues were integrated into an electronic, web-based decision tool that will assist utilities in understanding site-specific issues associated with retrofitting UV disinfection into their WTP. The UV Disinfection Implementation Tool (UVDIT) will be used to evaluate existing infrastructure, hydraulic limitations, water quality variability, power source limitations, and lamp breakage issues. The UVDIT was designed for filtered and unfiltered utilities using comprehensive decision trees that addressed these site-specific issues. These decision trees were created based on previously identified design issues, a risk analysis, and a utility survey. In the first step, the user inputs water quality, flow, and WTP configuration information. Based on this information, the UVDIT estimates the UV facility footprint, number of UV reactors needed, the size of these UV reactors, and the anticipated headlosses for the UV reactors and the entire UV facility. Using this information, the user then answers a series of questions about their existing infrastructure, hydraulics, preferences for addressing additional hydraulic requirements, power quality, pressure surge conditions, and cost indices (e.g., labor hourly rate). Based on this information, the following items are discussed in this paper: feasible retrofit locations for UV disinfection; potential risks of UV disinfection at each retrofit location; mitigation methods that may reduce these risks; estimated costs for each retrofit option; a cost comparison of the retrofit options; the UVDIT development process; the decision trees used to program the UVDIT; the cost assumptions; overview of how to use the UVDIT; and, one case study example that includes the inputs to and outputs from the UVDIT. Includes 4 references, tables, figures.