Introduction: Stable isotopes of water have extensively been used to understand hydrological cycle in natural environment, however their application in highly managed urban water systems have been limited. Recent research have shown that water isotopes reflect urban water management practices and have potential application in understanding urban water supply network dynamics, evaluating effect of climate variability on water resources, geolocation and water monitoring and regulation.

Jameel and colleagues ( WRR, 2016) attributed the strong and structured spatiotemporal variation in tap water isotope ratios of Salt Lake Valley (SLV) to complex distribution systems, varying water management practices and multiple sources used across the valley. Building on their result, we collaborated with the largest water supply company in SLV, Jordan Valley Water Conservancy District (JVWCD) and expanded our project which now includes predicting the source (or sources) contributing to a given supply area. The different sources supplying JVWCD (such as Provo River system, Wasatch Creeks and groundwater wells) have similar yet distinct isotope ratios, providing an excellent opportunity to test the robustness of water isotopes in monitoring distribution pattern of the sources in the supply system. For this project, we collected more than 100 samples/month (between April 2015-May 2016), from different water sources (creeks, streams and groundwater wells), water treatment plants (WTP), storage reservoirs and delivery locations along the supply lines across the water distribution area , measured their isotopic ratio and developed isotopic mixing models using Hierarchical Bayesian (HB) framework to understand the flow of water in an urban supply system and connect tap water at a specific location to its respective sources.

Data Collection Methods: Water samples collected from source, reservoirs, and different locations within the JVWCD service area.

Location of Data Collection: we collect approximately 100 samples per month. From May 2015 to April 2016, for each month, we sampled different sources supplying water to the JVWCD service area and at numerous locations on the JVWCD distribution line (subsequently referred to as supply sites). Source water samples were collected as effluent from the WTPs and from groundwater wells and supply sites samples were collected from monitoring taps positioned on the distribution line. Source and supply sites were sampled 1-3 times per month.

Data Analysis: For each site, samples were obtained by running the tap water for ~15 seconds before filling, capping and sealing (with parafilm) a clean 4 ml glass vial. Samples were analyzed for their isotopic composition within a few weeks of their collection at the Stable Isotope Ratios for Environmental Research (SIRFER), University of Utah, on Picarro L2130-i Cavity Ring Down Spectroscopy (CRDS) analyzer. All the sample values are reported using the δ notation, where δ=Rsample/Rstandard -1, R= 2H/1H and 18O/16O. Four injections of each sample were measured and corrected for memory effects, through-run drift, and calibrated to the VSMOW-VSLAP scale, using a suite of three laboratory reference waters (PZ: 16.9‰, 1.65‰; PT: -45.6‰, -7.23‰; UT: -123.1‰, -16.52‰; for δ2H and δ18O, respectively).