Decoupling Urban Water Use from Population Growth in the Colorado River Basin

Decreases in river flows and rapidly declining reservoir levels pose grave water security risks to urban water utilities reliant upon the Colorado River Basin. This study evaluated multidecadal trends (2000–2020) in urban water use for 28 utilities with a combined service population of 23 million people that depend in part or wholly upon water supplies from the river and its tributaries. It was found that more than half of cities surveyed have substantially decoupled their water demands from population growth by greatly reducing their per capita water use. Total water deliveries to the cities surveyed dropped by 18% even though their combined service population increased by 24%. Median per capita water-use rates for total and residential use decreased by 30% and 28%, respectively. The most common water conservation strategies included toilet replacement rebates and other plumbing retrofits, variable water-pricing structures, and turf removal. Given considerable variability in total per capita water use and rate of per capita reductions, many cities should be able to substantially reduce water demands to attain the per capita water-use levels of top performers. In contrast with overall declines in water use, utilization of the Colorado River Basin as a water source has not declined but instead increased by 1%. These results suggest that opportunity may exist for reducing pressure on the Colorado River Basin if per capita water-use rates continue to decline and utilities increase their use of other water sources—including water reuse, desalination, and stormwater capture as well as other rivers and aquifers—that can be prioritized over the use of Colorado River supplies.