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Study: Southwestern cities are using less water overall despite population growth

Melissa Sevigny

New research says many cities in the Southwest have reduced their total water use in the last two decades, despite drastic population growth. But these strides in water conservation haven’t helped the drought-stressed Colorado River. KNAU’s Melissa Sevigny spoke with the study’s author Brian Richter of Sustainable Waters.

So you looked at data from 28 water utilities that all rely on Colorado River water; what was the most surprising result from that examination?

Taken together collectively, we found that these cities have been able to reduce their total water deliveries, in other words, their total water use, by about 18% even while their populations increased by 24%. We found that to be a pretty miraculous outcome. That really suggests that these cities are making a lot of progress with their water conservation efforts.

That’s incredible and it’s very counterintuitive. Just quickly, how is that possible?

The most important things they have been investing in has been trying to, first of all, get their residents and businesses to reduce how much water that they’re using outdoors. Typically, these cities use—between 40-60% of all their water is going outside… That’s always the first and more important place to look when you’re trying to cut back on how much water they need.

In your research did any cities jump out at you at being particularly good or particularly bad at water conservation?

There are some all-stars. I think this is going to be a big surprise to a lot of your listeners, Las Vegas is at the top of pack…. And I would say in general, Melissa, what we found in our study was that the larger cities almost across the board are really doing a pretty phenomenal job of reducing their water use over the last couple of decades. Part of that is because they have the financial resources to really invest in water conservation…. That isn’t so much the case in the smaller cities. The smaller cities, I think, are being overwhelmed with very, very rapid growth these days, and they don’t have the fiscal resources, they don’t have the staff capacity, the expertise, to be able to invest in the same level as the larger cities have been in their water conservation activities.

So overall what does this mean for the Colorado River?

One of the disappointing findings was that when we started to break out the specific water sources that they were utilizing for city water supplies, we found that their use of the Colorado River Basin hasn’t decreased all that much… And overall across the board we found that when you roll up the 28 cities we looked at, the use of the Colorado River actually increased one percent.

Even though the overall water use is dropping, the Colorado River hasn’t really benefited from that.  

Right, which means they’re decreasing their use of other water supplies.  

What is the lesson from this? As we speak, there are folks gathering together to discuss what to do about the crisis on the Colorado River, what’s the takeaway you’d like them to know?

The takeaway is that it is quite feasible to maintain the same level of water use or actually reduce their water use even under tremendous pressure from population growth… but to really make this work for stressed water sources like the Colorado River, the utilities are going to have to shift among their different water sources and give the Colorado River some relief.… A lot of them are starting to invest in recycling their water, and that will be some important progress…. There’s a variety of other alternative water supplies they can tap into and reduce their pressure on the Colorado River.

Brian Richter, thank you for speaking with me.

You bet.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.