Water Quality Index (WQI) is one of the most powerful and effective tools for analyzing overall characteristics of water quality any reservoirs, its way to transfer information on water quality trends to policy makers and the general public is with Indices. Our objective was to evaluate ground water quality in the Rooppur Nuclear Power Plant (RNPP) area, Pabna, Bangladesh using a Canadian Council of Ministers of the Environment (CCME) WQI. WQI represent a clear scenario about the usability of the water for different purposes. Water quality indices are useful for concise information in order to achieve a national perspective. Attempts have been made to review the WQI criteria for the appropriateness of drinking water sources. Till now any methodology is not developed for evaluation of water quality index purposes in Bangladesh. At the very recent a few researcher try to use WQI method for giving WQ rating in Bangladesh. But, has no specific guideline for indexing water resources. This study to explore a potential WQ indexing method which applies easily and measure overall WQ for managing purposes. Besides, the present article also highlights and draws attention towards the development of a new and globally accepted "Water Quality Index" in a simplified format, which may be used at large and could represent the reliable picture of water quality. In the present paper, water quality index (WQI) was estimated for the groundwater of Rooppur Nuclear Power Plant area within the study period. The study also identifies the critical pollutants affecting the groundwater quality during the study period. The indices have been computed for the winter season at 17 locations, namely GW1, GW2, GW3 etc. It was found that the water quality ranged from poor to marginal category at all locations. Alkalinity, Conductivity, BOD, DO, Iron, Arsenic, Lead, Nitrite and fecal coliforms were found to be critical parameters.