STABLE ISOTOPE RATIOS DOCUMENT COMMUNITY-SCALE STRUCTURE AND CONNECTIVITY IN PUBLIC WATER SUPPLY SYSTEMS

Public water supply systems are the life-blood of urban areas, accessing, managing, and distributing water from an often complex array of sources to provide on-demand access to safe, potable water at the point-of-use. Water managers are faced with a wide range of potential threats, ranging from climate change to infrastructure failure to supply contamination. Information on the structure of supply and conveyance systems, connectivity within these systems, and links between the point-of-use and environmental water sources are thus critical to assessing the stability of water supplies and responding efficiently and effectively to water supply threats. We report a novel new dataset of stable isotope measurements from a large number of public-supply waters in three large, urban or urbanizing areas in Utah. Samples were collected in a series of ‘blitz’ sampling campaigns, and document snapshots of regional water supply patterns and characteristics at the community scale. Significant differences in the spatial structure of the isotopic data are seen between the greater Salt Lake and Logan metropolitan areas, and can be related to differences in the degree of centralization of water management in these areas. Discrete water management units in the Salt Lake metropolitan area can be identified and mapped in detail based on unique combinations of H, O, and Sr isotope ratios deriving from specific water sources used by these providers. Providers that use or blend water from surface reservoirs can be identified based on evaporative effects on H and O isotope ratios, which increase systematically between spring and fall sampling periods. The isotopic data provide direct information on water sources, distribution and connectivity within these public supply systems but also fingerprint the water leaving these systems, offering a basis for tracing this water as it enters hydrological, ecohydrological and atmospheric systems through direct application, indirect processes associated with use (e.g., evaporation, runoff, infiltration), or inadvertent loss (e.g., via leaky infrastructure).