ANALYSIS OF STABLE ISOTOPES AND TRACE METALS IN TAP WATER TO COMPARE HYDROLOGICAL CHARACTERISTICS OF THE BOSTON AND NYC WATERSHEDS

Stable isotope ratios in drinking water serve as valuable tools for mapping the hydrology of a drinking water supply system. A surface water reservoir has a discrete mean isotopic signature at a given time, which depends on the isotopic composition of the precipitation inputs (rain and snowfall) that fluctuate in accordance with monthly meteoric patterns. Spatial and temporal hydrological mapping of the Quabbin and Wachusett Reservoirs (water supplied to Boston residents), and the Catskill, Delaware, and Croton Watersheds (water supplied to New York City residents), remains poorly constrained. Thus, the knowledge of water source and time traveled in water mains is generally elusive. Additionally, human activity and continued prevalence of lead service lines in older urban areas result in both the natural and unnatural occurrence of trace metals in tap water. This toll varies household to household, depending on the make-up of each private service line, and how corrosive the water is. Presence of lead and heavy metals in drinking water is harmful, and sometimes even lethal to sensitive groups, such as children. Here, we collected tap water from residents of Boston and NYC over the course of several months. Using isotope ratio mass spectrometry, we demonstrate how stable isotopic composition (δ¹⁸O, δ²H) of a surface water body changes over time along a “local meteoric water line,” which has a unique slope and y-intercept for a given watershed. It is expected that our δ¹⁸O versus δ²H plots will demonstrate linear monthly trends along different slopes of meteoric water lines between the Boston and NYC metropolitan areas. Thus, we will be able to glean information on how long the water remained in a water distribution system before delivery to individual household taps in each of these two cities. We also employ an inductively coupled plasma mass spectrometer (ICP-MS) to measure trace metal concentrations within these water samples. Our methods of collection allow for a manner of simultaneously characterizing both the hydrology and water quality parameters for the drinking water supply in two different metropolitan areas.