As climate change progresses and populations soar, effective resource management is essential to ensure that water needs are met. This is especially true for arid urban regions, such as Utah’s Salt Lake Valley. In a recent study, Jameel et al. analyzed the valley’s water system for stable isotopes, demonstrating that the technique may be useful for urban water management worldwide.
Salt Lake Valley, which comprises Salt Lake City and its suburbs, is home to more than 1 million people, and this number will nearly double by 2060. The valley experiences dry, warm summers and cold, wet winters. Like other metropolitan areas with dry climates and large populations, the region relies on a variety of water sources—including creeks, river reservoirs, and wells—and a complex water distribution system.
Every spring and fall between 2013 and 2015, the researchers collected tap water samples from homes, businesses, and public buildings across the valley. In total, the team collected more than 800 samples.
Then, they measured levels of oxygen and hydrogen isotopes in each sample—a technique commonly used in natural environments to track the fate of water from different sources. However, in an urban setting, the researchers found that tap water isotopes can provide a wealth of detailed information on the water management practices used throughout the valley.
For example, they could distinguish between districts using local water and those using a mixture of local and transported water. The researchers were also able to estimate the fraction of nonlocal water used in districts that rely on a mixture. The isotopic information may provide an observational technique to evaluate water distribution systems and spot connections between water and environmental sources in systems where water supply infrastructure information may be considered proprietary, difficult to obtain due to security concerns, or simply lacking, as it is in many cities in developing countries.
The isotopic ratios also reflected demographic factors like population. For example, cities with populations above certain thresholds were more likely to use nonlocal water.
The ratios also gave clues to household incomes. Water isotopes in a town with a median income of roughly $40,000 per year differed from those in a town with a median income of approximately $80,000 per year. This difference may have to do with the usage of high-quality surface water in wealthier neighborhoods or the geographic and historic structure of the urban area—many of the affluent areas are situated closer to mountain surface sources and within areas of earlier development, which often retain historic allocations of surface water rights.
Relationships to income and population highlight the ability of water isotopes to capture the association between demographics and water management practices in an urban setting.
Shifting isotope levels also reflected water lost to evaporation during a dry period that lasted throughout the study. Thus, the authors explained, fluctuations in isotope levels over time may indicate whether water systems are under environmental stress.
The authors suggest that measuring stable isotopes could be used in many ways to improve water system monitoring and management. For example, it could aid in cases involving water rights, environmental justice, or contamination. It could also help validate water systems’ operational processes. Finally, it could provide valuable information to help urban regions plan for water stress caused by climate change. (Water Resources Research, doi:10.1002/2016WR019104, 2016)
—Sarah Stanley, Freelance Writer