A new water mass analysis technique is used to analyze the BCTS data set in the Bhavnagar city of ten years for changes in Water properties. The technique is based on a sequential quadratic programming method and requires careful definition of constraints to produce reliable results. Variations inwater properties viz., temperature and salinity observed in the water are used to define the constraints. It is shown that to minimize the residuals while matching the observed temperature and salinity changes in the source region the nitrate concentration in the water has to be allowed to vary as well. It is concluded that during the period of investigation nitrate underwent significant variations in the city water properties.