Forest management objectives in public water supply areas are designed to optimize water quality. We employed a paired-tree sampling approach within mixed stands to test the effects of evergreen conifer versus deciduous angiosperm taxa on water chemistry beneath canopies (i.e., throughfall; TF) in a post-industrial region with Ca-impoverished acidic soils and pronounced coastal weather conditions. Reduced concentrations of protons and sea salt were two discernable benefits of deciduous angiosperm trees. These effects became more pronounced during fall recharge when tree physiological dormancy coincided with onshore storm events and increasing seasonal demand for industrial and residential coal combustion. Taxon differences however, did not exert any significant effect on base cation proportions in soil leachates and on soil cation exchange complexes. Thus, ecosystem-based management of stand-level tree diversity in public water supply areas should monitor pH and electrical conductivity of TF water to mitigate adverse water quality effects of persistent acidifying air pollution and the preponderance and high concentration of Na+ in coastal regions. Results largely corroborated previous observations of a decreasing trend in acidifying air pollution at the northeastern periphery of the Eastern Deciduous Forest biome, although elevated SO42−/Cl− – ratios above seawater levels were still noted in TF water chemistry. Electrical conductivity was a reliable predictor of Cl− concentration in TF water regardless of taxon, phenology, and stand location (R2 = 0.99).