Water quality indices (WQI) were introduced aiming at giving a single value to the water quality of a source, thus reducing great amount of parameters into a simpler expression . In this book, an attempt has been made to devise a methodology to analyse various water quality parameters and then integrate them with WQI and Geographic Information System (GIS) for an effective interpretation of the quality status of groundwater by taking Delhi as a case study. Physical and chemical analysis of groundwater of Delhi was conducted and results interpreted using WQI and finally translated in sensitivity maps using GIS. The book delves in understanding water quality assessment and should be useful for anyone interested in groundwater quality issues from general public and students to policy makers.