A study from the University of California, Riverside, has found that after a drought-stricken California lifted a year of mandatory water-use cuts, residential water use crept back up somewhat, but the overall lasting effect was a more waterwise Golden State. Published in the journal Water Resources Research, the UCR study found that water use by 2019 was still lower than it was in 2013, thanks in large part to behavioral changes by those who had been using the most water. We sat down with Dr. Mehdi Nemati, the study's lead author, to talk about the study and what its results mean for the residents, governing bodies, and municipal organizations in California.
Q: WHEN THERE'S A DROUGHT, WHO MAKES THE JUDGEMENT CALL THAT A CONSERVATION MANDATE SHOULD BE IMPLEMENTED?
A: In California, that falls to the Office of the Governor, the State Water Resources Control Board, and the Department of Water Resources. Together they make the decision to do one of two things. The first is a voluntary reduction, and the other is a mandatory reduction. When the Office of the Governor issues a drought emergency, this releases funding for the water agencies to invest in conservation and other sustainability projects. It also gives the State Water Resources Control Board the authority to require water agencies to report their water use levels and so on.
Q: CAN YOU EXPLAIN WHAT YOU MEAN BY REBOUND EFFECT?
A: During a serious drought, there are big pushes for a reduction in water use, but when the drought appears to be over, then people think that it's fine to use water again. For example, in 2013/2014, when there was a conservation mandate, we saw a 25% reduction in water use, but then in 2017/2018, water use levels started to creep back up again. Not to the same pre-drought levels, but it does start to rebound.
Q: DESCRIBE THE DATA THAT YOUR TEAM USED FOR THIS ANALYSIS.
A: We studied data from a midsize water utility in Northern California that serves about 20,000 households. We focused on single-family residential because that's the majority of the water used by that water agency. Fortunately, they monitor hourly water consumption in addition to the monthly meter, and they have advanced metering infrastructure as well. So they produce millions of data points to see not only if the reduction happened but what was the rebound effect. If there is a behavioral change, we can also observe that from the data.
Q: SPEAKING ABOUT AVERAGE HOURLY WATER CONSUMPTION, HOW DID THAT CHANGE POST-MANDATE?
A: First of all, we did see that there is there's a rebound effect, so we see reductions during the mandate, and then it starts to come back up. But we also see a shift in the hours of consumption. The utility that we were studying was educating residents to water earlier in the day rather than later. This resulted in a reduction of water use, but also a shift in the distribution to the earlier hours. We see a lot of watering happening and all the outdoor watering early in the morning rather than later. 8:00 or 9:00 in the in the morning was the norm pre-mandate, which shifted to 4:00-5:00 am during and after the mandate, which is better because you're not losing water to the evaporation. (Most agencies now recommend watering in the evening.) This reduction could be a product of the agency's messaging or could be that there were restrictions on watering during certain hours.
Q: WHAT DO THESE FINDINGS MEAN FOR WATER UTILITIES? HOW CAN THEY APPLY THIS TO HOW THEY OPERATE AROUND DROUGHTS?
A: Based on what we’re seeing, what that means for the water agencies is that next time there is a drought and there's a call for reductions, there may not be much low-hanging fruit left. People already got efficient appliances, maybe installed a smart sprinkler, or made some behavioral changes, but it's going to be harder and harder to make additional reductions as we move forward. So we have to think about innovations on their part. The second takeaway is that their messaging is working, at least with regard to watering at better times of the day. That's great. There are also certainly financial implications because all of the utilities in California Public Utilities must recover their costs. If there are fewer sales, even after the drought is over, that’s something they will have to prepare for. So you have to think about what this means financially and make investments in the future, like better infrastructure, for example.
Q: THE FINDINGS SUGGESTED THAT PEOPLE WHO USED THE MOST WATER BEFORE A WATER MANDATE SHOWED A SLOWER REBOUND EFFECT THAN THOSE WHO WERE ALREADY USING LESS WATER. CAN YOU EXPLAIN THAT?
A: This relates to factors like income status, the type of house and acreage, etc. It seems that residents who use more water are typically more affluent and tend to have higher education. So they're adopting technology when there is a call for reduction and are continuing to use that after mandates have been lifted, minimizing any rebound effect. This is what we call efficiency gains. Efficiency means that there's not going to be a rebound; it's not short-term. But for those that used less water to begin with, when a conservation mandate is issued, they often let their yards go brown, then once the mandate is over, we see a larger rebound effect to try to recover their yards and greenery.
Q: FOR RESIDENTIAL USERS, WHAT'S THE BIGGEST DRAIN OF WATER?
A: Indoor water use has been largely cut through rebates for water-wise appliances, like low-flow toilets and high-efficiency washing machines. However, residential outdoor water use in the U.S. accounts for nearly 8 billion gallons of water each day, mainly for landscape irrigation.
It's getting harder to conserve, but there are still so many opportunities outdoors, by replacing traditional lawns with drought-tolerant native plants or using weather-based irrigation. However, that brings up a disparity when it comes to the effects of water conservation in more affluent areas vs low-income areas. In low-income areas, single-family homes with yards often let their lawn go brown, while higher-income areas adapted through technology, using smart sprinkler controllers triggered by weather data to only water at night or skip watering during or after rain events. These are some of the unintended consequences of conservation mandates, especially in disadvantaged communities or these communities that cannot afford to adopt new technology.
Q: WHAT WAS THE MOST INTERESTING OR SURPRISING FINDING TO YOU?
A: To see the shift in watering times was pretty impressive since it was essentially across the board. People had changed their behaviors. Again, that could be because of the educational material they sent out or it could be that people were trying to follow the watering restrictions in their district. The other surprise was this rebound effect in lower income versus higher income water users because, again, that speaks to the role of technology and if you're able to afford to adopt these innovative new technologies.
Read the full research article from Water Resources Research here.
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