DETERMINING THE SPATIAL INFLUENCE OF IMPORTED AND LOCAL WATER SOURCES TO MUNICIPAL TAP WATER SYSTEMS AND HUMAN HAIR IN THE SOUTHWESTERN UNITED STATES USING STABLE ISOTOPES OF OXYGEN AND HYDROGEN

In arid and semi-arid parts of the southwestern USA, imported waters derived from large canal systems like the Colorado River Aqueduct, Los Angeles Aqueduct, and the California Aqueduct service a significant component of the regional water needs. These waters are sourced primarily from high altitude snowmelt runoff and have relatively low annually averaged stable isotope ratios of hydrogen and oxygen (δD, δ18O) (-99 to -127‰, -10 to -13‰,) when compared to water derived from local rainfall and surface river sources (-35 to -42 ‰, -5 to -7‰) in southern California, western Arizona, and southern Nevada. The distinct isotope signatures of these two waters can be used to differentiate the two sources in tap water from municipal systems. In this study, samples of tap water, aqueduct water, and surface water were collected throughout the Southwest to produce a series of maps of the spatial influence of imported water in municipal tap water. This data was then be used to develop mixing models to determine the relative importance of imported water regionally, and track the prominence of the movement of these imported waters after initial use and addition to a system. Additionally samples of human hair were collected and analyzed to discern this imported water signal in the human population. The use of isotopes to trace this anthropogenically introduced water is of interest to water management, resolving water rights issues and disputes, as well as environmental applications in ecological and forensic studies. Additionally these tracing methods may be applied worldwide in areas where the movement and dynamics of hydrologic systems are either unclear or unknown.