Jay L. Banner

Growing water scarcity is driving many drinking water suppliers to mix water from different sources, increasing risks of pH-, redox-, and mineral-equilibrium water quality issues. Residents of Austin’s Colony (central Texas) have received hard water and intermittent discolored water for over a decade and face high water rates, bottled water costs, and appliance maintenance costs. Supply comes from a local shallow alluvial aquifer and a deeper sandstone aquifer 85 km away. We used Community-Based Participatory Research (CBPR), involving academics, residents, and community organization staff, to investigate the extent and causes of water issues in Austin’s Colony. We conducted community meetings, surveys ( n = 100), and bacterial and chemical analyses (cations, anions, Sr isotopes) of tap water samples ( n = 78). CBPR was essential for defining objectives, recruiting participants, and water sampling. Most survey participants (70%) reported discolored water events, and only 7% drink untreated tap water. Al, Mn, Fe, Cu, and Pb concentrations exceed regulatory limits in water samples, but were below regulatory standards in in-home treated samples. Geochemical analysis shows that the water composition at each household varies based on mixing between two or three groundwater sources, with the alluvial aquifer providing most of Ca and Mg driving hardness. Through mixing models and spatial analysis, we link household water quality to spatial location within the distribution network and identify groundwater mixing as the principal control on water quality. Mixing may also drive water quality changes associated with corrosion and mineral precipitation within the network, which, along with water turbulence, may explain discoloration events. Increased use of the Carrizo-Wilcox aquifer will likely reduce hardness and discoloration. This high-spatial-resolution geochemical mixing approach can inform water management in other distribution networks that mix different water sources. We highlight the importance of monitoring household water quality and evaluating practices to address water scarcity in rapidly growing areas.

Cities and urban areas present important opportunities for advancing toward sustainability and resilience goals. From a systems perspective, various targets and indicators of key outcomes reflect sustainability of urban areas, motivating consideration of local and regional context. We explore four key themes for creating sustainable urban areas: 1) urban areas are complex systems linked with diverse rural areas across the urban-rural gradient, 2) data and modeling of physical and non-physical systems can aid decision making for sustainability, 3) creating sustainable urban-rural systems requires collaboration with partner communities, and 4) change requires adaptive and transformative governance frameworks. These themes guide sustainability innovations through co-production of knowledge among communities, authorities, managers, and researchers. The sustainability of urban areas strongly depends on urban-rural connectivity regarding both physical systems and governance frameworks.

Austin, Texas is among the most rapidly urbanizing regions in the U.S., posing challenges to the resilience of its water resources. Geochemical differences between stream water from relatively pristine (rural) and impacted (urban) watersheds indicate several distinct controls on stream water compositions, including extent of urbanization, extent of failure of the city’s municipal water infrastructure, and differences in bedrock composition and permeability. We focus here on the largely unstudied evolution of municipal water once it leaves the infrastructure and enters the natural hydrologic system as groundwater and/or surface water. We use the distinct Sr isotope values (⁸⁷Sr/⁸⁶Sr) and other compositional differences between municipal waters, natural stream and spring water, limestone bedrock, and soils as tracers of the sources of and processes by which four Austin-area streams and springs acquire their dissolved constituents. These processes include 1) fluid-mixing between municipal and natural surface water and groundwater, 2) multiple mineral-solution reactions, including dissolution and water-rock interaction (WRI) processes of precipitation, incongruent dissolution, and recrystallization, and 3) varying groundwater residence times. Stream water in two urbanized watersheds have high ⁸⁷Sr/⁸⁶Sr values and ion compositions close to values for municipal water, whereas stream and spring water in two rural watersheds have compositions close to natural stream water. Urbanized stream water compositions can be accounted for by models of municipal water contributions followed by dissolution of bedrock minerals. By contrast, rural stream water compositions are consistent with a model sequence of dissolution followed by extensive WRI with limestone. The results of this study indicate significant contributions to streams from the municipal infrastructure. We find that the evolution of this municipal water in the natural hydrologic system comprises multiple fluid-mixing processes and mineral-solution reactions, which are influenced by differences in bedrock geology. This composite evolution advances our understanding of the complexities of “Urban Stream Syndrome”.

Developing sustainable urban systems is a fundamental societal challenge for the 21st century, and central Texas faces particularly synergistic challenges of a rapidly growing urban population and a projected increasingly drought-prone climate. To assess the history of urbanization impacts on watersheds here, we analyzed 51 cores from bald cypress trees in paired urban and rural watersheds in Austin, Texas. We find a significant contrast between rural and urbanized watersheds. In the rural watershed, tree-ring-width growth histories (“chronologies”) from 1844–2018 significantly and positively correlate (p < 0.01) with (1) one another, and (2) regional instrumental and proxy records of drought. In the urbanized watershed, by contrast, chronologies weakly correlate with one another, with instrumental records of drought, and with the rural chronologies and regional records. Relatively weak drought limitations to urban tree growth are consistent with the significant present-day transfer of municipal water from urban infrastructure by leakage and irrigation to the natural hydrologic system. We infer a significant, long-term contribution from infrastructure to baseflow in urbanized watersheds. In contrast to the common negative impacts of ‘urban stream syndrome’, such sustained baseflow in watersheds with impaired or failing infrastructure may be an unintended positive consequence for stream ecosystems, as a mitigation against projected extended 21st-century droughts. Additionally, riparian trees may serve as a proxy for past impacts of urbanization on natural streams, which may inform sustainable urban development.

Developing sustainable urban systems is a fundamental societal challenge for the 21st century, and central Texas faces particularly synergistic challenges of a rapidly growing urban population and a projected increasingly drought-prone climate. To assess the history of urbanization impacts on watersheds here, we analyzed 51 cores from bald cypress trees in paired urban and rural watersheds in Austin, TX. We find a significant contrast between rural and urbanized watersheds. In the rural watershed, tree-ring-width growth histories (‘chronologies’) from 1844-2018 significantly and positively correlate (p < 0.01) with 1) one another, and 2) regional instrumental and proxy records of drought. In the urbanized watershed, by contrast, chronologies weakly correlate with one another, with instrumental records of drought, and with the rural chronologies and regional records. Relatively weak drought limitations to urban tree growth are consistent with significant present-day transfer of municipal water from urban infrastructure by leakage and irrigation to the natural hydrologic system. We infer a significant, long-term contribution from infrastructure to baseflow in urbanized watersheds. In contrast to the common negative impacts of ‘urban stream syndrome’, such sustained baseflow in watersheds with failing infrastructure may become an unintended positive consequence for stream ecosystems, as a mitigation against projected extended 21st century droughts. Riparian trees may serve as a proxy for past impacts of urbanization on natural streams, which may inform sustainable urban development.

Background: The 100th Meridian in Texas aligns with a corridor of large and rapidly growing urban areas with a growing water demand and limited supply. Understanding the variations in residential water consumption may assist with identifying the characteristics associated with disproportionate water consumption that may be responsive to policy changes and enforcement. Methods: Data from the San Antonio Water System, the Bexar County Appraisal District, and the American Community Survey were utilized. The average daily water consumption was estimated for the seasons and a total year for more than 300,000 single-family residences between 2009 and 2015. The presence of a swimming pool, residential parcel hectares, size of the living space, and per capita income were examined as predictors of the variations in residential water consumption using hierarchal modeling. Results: The presence of swimming pools and a residential property’s value were the strongest predictors of water consumption. Parcel hectares and household income were positively associated with water consumption. A quartile analysis of select independent variables identified the disproportionate variations of water consumption of units with large yards, swimming pools, and high values. Conclusions: The findings indicate a strong association between variations in residential water consumption and both irrigation and swimming pool water used, which emphasize a need to focus conservation efforts on higher-valued housing and residences with swimming pools and the consideration of tiered pricing.

Quantifying urban development impacts on fresh water quality and quantity is critical, especially as growing populations concentrate in urban centers and with climate change projections of increased hydrologic extremes. We investigate geochemical processes through which municipal supply and waste water, carbonate bedrock, and soils impact stream and spring water compositions within the Bull Creek watershed (Austin, Texas). This watershed exhibits a sharp geographic divide between urban and rural land. Urban and rural waters were assessed to quantify relative influences of municipal water on stream and spring water elemental compositions and ⁸⁷Sr/⁸⁶Sr values. Higher ⁸⁷Sr/⁸⁶Sr for samples from urban sites relative to rural sites can be accounted for by two processes: (1) water leakage from municipal infrastructure and/or irrigation or (2) ion exchange as precipitation infiltrates through soils with varying ⁸⁷Sr/⁸⁶Sr. Irrigated soils have higher ⁸⁷Sr/⁸⁶Sr than unirrigated soils, indicating that irrigated municipal water resets soil compositions and that process (1) is a dominant driver of urban stream and spring water evolution. Geochemical modeling results indicate that urban waters consist of 50% to 95% municipal water. Geochemical modeling further demonstrates the evolution of municipal water as it infiltrates as groundwater and undergoes water‐rock interaction. These results are compared with groundwater compositions on a regional scale to infer local flow paths and relative groundwater residences times of municipal water. This study provides a geochemical modeling framework that quantifies both the significance of municipal water on urban stream water and soil compositions and the role of municipal water within urbanized watersheds and aquifers.