Big Cities Are Downsizing Their Water Footprints

Photos above: Forty percent or more of all water use in western US cities goes to outdoor watering of lawns, gardens, pools, and golf courses. One of the most effective urban water conservation strategies is to reduce the area of irrigated landscaping, or switching to less water-intensive vegetation.

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My research group spent three years collecting water data and other information from 28 water utilities that serve a total of 23 million people in the American Southwest. The task wasn’t easy: 39 researchers were involved in collecting data from 45 different utility employees. Each of these utilities we surveyed is dependent on the Colorado River for some portion or all of their water supplies. You can find our full results in this paper from the Journal of Water Resources Management & Planning.*

Overall, cities dependent on the Colorado River have done a fantastic job of managing their total water use under very high rates of growth. They’ve cut their water use by 18% while their populations grew by a whopping 24% during 2000-2020.

Big cities are doing a much better job with water conservation than smaller cities. Cities with more than 1 million residents cut their water use by an impressive 24% but water use in small cities actually grew by 3%. This is due to two factors: smaller cities are growing very fast, yet they don’t have the financial capabilities to invest in water conservation programs.

Key to big water savings is being able to get your customers to substantially reduce their average daily use of water, known as “Gallons Per Capita per Day” (GPCD). On average, big cities (>1 million pop.) were able to lower their Total GPCD by 35%. Medium cities (100,000-1 million pop.) lowered their GPCD by 30%, and smaller cities (less than 100,000 pop) lowered it by 25%.

But even with impressively lower per-capita needs, smaller cities simply grew too fast (median=42% growth) to keep their overall water demands in check.

Some of the primary water conservation strategies being applied in these 28 cities include offering rebates for replacing old water-guzzling toilets and other plumbing fixtures, and paying homeowners and businesses to rip out lush green lawns and replace them with drought-tolerant and often native shrubs, flowers, and grasses. Many cities also used water rate structures to control water use, such as by increasing the cost per gallon as water use rises.

Not Much Help for the Colorado River, though….

Unfortunately, those impressive water conservation efforts didn’t do much for the Colorado River, because total use of the river by the 28 cities we surveyed actually increased slightly during 2000-2020. That means that cities are taking less water from other water sources — such as their local rivers or from groundwater, or from desalination or water reuse — but not reducing their pressure on the Colorado River.

Water Conservation is Still Largely Untapped

Based on the fact that per-capita water use varied greatly among our 28 cities (low of 80 to a high of 286 in Total GPCD), there’s clearly room for the under-performing cities to tighten up their water belts. In larger cities, there is still great potential for reducing outdoor water use, or tapping into ‘alternative’ water supplies, such as reusing water more thoroughly, capturing stormwater, or encouraging homeowners and businesses to harvest rainwater.

The Southern Nevada Water Authority — which supplies water to nearly 1.4 million residents in Las Vegas, Nevada — is a great example of water conservation’s potential. During 2000-2020, the city reduced its total water use by 10% and lowered its Total GPCD by 47%, even while its service population grew by a staggering 69%! Yet the water authority has set an admirable goal of lowering its GPCD by another 23% by 2035.

*Note: If you are unable to access our paper using the link in the first paragraph above, please drop me a note at brian@sustainablewaters.org and I’ll send you a copy.