As the principal United Nations body on environment, the UN Environment Programme (UNEP) had been tasked by UN-Water to lead on freshwater quality and aquatic ecosystem data and information inputs to the World Water Assessment Programme, and the main WWAP output, the World Water Development Report series. Part of this task involves developing global water quality indicators and ultimately, a global water quality index. UNEP delegated this responsibility to its GEMS/Water Programme, with direction to convene an international experts’ workshop designed to implement the indicators and index requirements. The workshop, attended by a group of selected indicator specialists, was convened at IAEA headquarters in Vienna, Austria (May 4th – 6th 2005) with the objective of reviewing the topic of water quality indicators/indices and making recommendations and suggestions on approaches and actions that GEMS/Water might consider in its future operations. The experts’ first recommendation was that GEMS/Water should develop a pilot study to develop an index to assess the global status of drinking water in source water supplies (UNEP GEMS/Water, 2005). The experts’ recommendation report is available on the GEMS/Water website. This report presents the results of implementing the experts’ first recommendation. It outlines an approach taken to develop a global water quality index, as well as preliminary sensitivity analysis and validation of the index against real water quality data. Limitations to the index are discussed, as well as next steps.