Water quality indices are necessary for resolving lengthy, multi-parameter, water analysis reports into single digit scores. This, in turn, is essential for comparing the water quality of different sources and in monitoring the changes in the water quality of a given source as a function of time and other influencing factors. In this paper we present the computer-automated tool QUALIDEX (water QUALIty inDEX), which has been developed by us to generate and operate water quality indices. Several popular indices--such as the Oregon Water Quality Index developed in the 1970s by Oregon Department of Environmental Quality and later updated in 1995, the Aquatic Toxicity Index developed by Wepener and coworkers for protection of aquatic life at the Olifants river, Kruger National Park, South Africa, the water quality index developed by Dinius in 1987, the Overall Index of Pollution (of surface waters) developed at the National Environmental Engineering Research Institute (NEERI), and the water quality index of the Central Pollution Control Board (CPCB)--have also been added to QUALIDEX in modular form. There is also a New water quality index sub-module which enables the user to generate his or her own index and compare its performance with these well-known indices. The package is also capable of analyzing the variations in the water quality of different sites at different times. The software has been coded in Visual C++ and has been integrated with MS Access database.