This work seeks to establish a regional-scale monthly record of the stable isotopic composition of ground and surface water in Massachusetts. By leveraging insights based on our previous hydro-climatic work (Weider and Boutt, 2010) and documenting the seasonal stable isotopic variability of these waters, we can assess important constraints on the seasonality of recharge, ground water residence times, sources of water to streams, and understanding the sensitivity of stream baseflow to seasonal hydrologic variability. We will gather existing regional isotopic measurements of precipitation, ground and surface waters combined with analyses collected in this work.