Drinking water quality management is a challenging task for water suppliers due to changing land use, human practices, and climate patterns. This dissertation seeks to provide tools for water managers to support the decision-making process. The first chapter consists of the investigation of water quality patterns at the Wachusett drinking water supply watershed, MA, USA, assessing nutrients and road salt trends at the surface water level, incorporating land use analysis to identify potential sources of pollutants in the natural environment. Land use data suggest association with altered drainage landscapes as potential sources of increased constituent transport. Despite watershed programs aimed at reducing salt applications, conductivity is increasing in streams, indicating a long-term legacy of salt accumulation, as is the case in many Northeastern watersheds. To better understand trends, the second chapter consists of characterizing the temporal and spatial distribution of salinity in freshwater across Massachusetts. This assessment shows that higher levels of electrical conductivity (EC) in surface water are related to the higher presence of urbanized areas. The size of the drainage area can contribute to dilution processes in the streams, attenuating these trends for larger basins. To better elucidate surface-subsurface water interactions and contaminant pathways in water systems, in the third chapter the pathways by which groundwater concentrations of salt indicators may be increasing in the Wachusett watershed are assessed using stable water isotopes. The analyses indicate that the groundwater recharge is winter dominant, thus the applied road salt during winter months can contribute to sustained increases in conductivity in the groundwater. Finally, investigating surface and groundwater concentrations allows water quality assessments using reservoir modeling to evaluate scenarios considering changes in management of local salting practices. The goal of the last chapter is to estimate the impact and the time to observe effects of pollutant migration in a watershed after remediation strategies would be implemented to provide the tools to achieve water management goals. Results indicate that efforts of reducing salt application should target the subbasins with the highest flows, however it is crucial to manage high concentration subbasins due to acute toxicity for aquatic life.