Heather Cooley: The Untapped Potential of California’s Water Supply: Efficiency, Reuse, and Stormwater
Recent study by the Pacific Institute and the NRDC show that there is potential water savings equivalent to 10.8 to 13.7 MAF per year
At the Bay Delta Science Conference held last fall, Heather Cooley from the Pacific Institute gave a presentation entitled, “The Untapped Potential of California’s Water Supply,” which draws on a series of reports jointly released by both the Pacific Institute and the Natural Resources Defense Council that looks at the opportunities for expanding California’s water supply through urban and agricultural efficiency, water reuse, and stormwater capture.
Ms. Cooley began by acknowledging the work she would be presenting is the work of a number of people at the Pacific Institute, the NRDC, and others.
“The key findings of our work are that there has been considerable progress in California in both capturing efficiency improvements but also through boosting and developing local supplies,” she said. “However, we are living beyond our means; we are taking too much water from our rivers, streams, and aquifers, but there is some good news in that there are still remaining in California large opportunities to reduce urban and agricultural water demand through efficiency improvements and opportunities to boost local supplies through stormwater capture and water reuse.”
To set the stage for her presentation, she first gave some basic data about water use in California, noting that this is from data pulled from the California Water Plan. Human water use, both urban and agricultural, is about 44 million acre-feet per year, of which about 80% of that is for agricultural and 20% for the urban sector, she said.
In the urban sector, average per capita demand is 230 gallons per person per day, but there is considerable variability in that. “In some areas, it’s in excess of 800 gallons per person per day, but that tends to be in areas that are not very densely populated and have a lot of golf courses and other high water use activities in those areas,” she said. “There are areas also on the coast where urban water use is considerably less, around 170 gallons per person per day in San Francisco up to 190 in the South Coast.”
She noted that in the urban sector, about two-thirds of water use is residential use, which is pretty evenly split between indoor and outdoor use. In addition to that, large landscapes and the commercial, industrial, and institutional use water as well.
“There’s clear evidence in California that we are living beyond our means,” she said. “The Colorado River is an example of that. We use some Colorado River water in California, and the Colorado River no longer reaches the sea. There are efforts underway to restore parts of the San Joaquin River, which was dewatered as well, and one getting an increasing amount of attention is groundwater.”
She then presented a graph showing groundwater losses in the Central Valley over the last 50 years. “What we can see from this is that we tend to drawdown groundwater in dry years, and we tend to recharge it in wet years. The challenge has been that we aren’t recharging as much in wet years as we have withdrawn in dry years and that has led to a long-term decline in groundwater levels in many, but not all, parts of the state.”
She noted that the cumulative loss of groundwater over the past 50 years is 56 million acre-feet. “It’s a considerable loss over that period and there is evidence that those losses are increasing,” she said.
Ms. Cooley said that the good news is that there are opportunities to reduce demands on both our surface and groundwater systems. “As part of our study and analysis, we looked at the technical potential in California currently to reduce demand through urban and ag efficiency and to boost supplies through water reuse and stormwater capture,” she said.
Urban efficiency potential
Current urban water use varies from year to year, but it’s about 9.1 million acre-feet, said Ms. Cooley. “For this study, we looked at the opportunities for reducing that use by installing more efficient appliances and fixtures in California’s homes and in businesses,” she said. “We looked at opportunities if all Californians were using water sense appliances and fixtures … and at the opportunities if people were using energy star products. We found that there is still considerable efficiency potential in California across every sector. We’ve done a lot on the residential indoor sector in particular, but we still find considerable savings there on the order of 1.3 to 1.6 MAF per year.”
Since about half of urban use is outdoors, there are opportunities there by installing more water efficient and more appropriate landscapes for California, as well as opportunities, both indoor and outdoor, in the commercial and institutional sectors. “In combination, we find that the potential savings on urban efficiency range from 2.9 million to 5.2 million acre-feet per year. I want to reiterate that this is the technical potential – this is if all Californian homes and businesses had these more efficient devices and installed, and it’s based on today’s population, so as the population the grows, the potential savings could be even larger.”
In terms of how those savings are distributed around the state, the largest potential in absolute number is in Southern California, she said. “Southern California has invested in and made considerable efficiency improvements, but the population is so large that the absolute water savings is the highest there, but there are potential efficiency savings across the state.”
“Current residential water use in California is about 140 gallons per person per day, and again that varies depending on where you are around the state,” Ms. Cooley said. “Residential savings can be found both indoors and outdoors with the largest savings outdoors. There are opportunities to reduce per capita outdoor demand in the residential sector by 20 to 50 gallons per person per day, and that’s by removing lawns and putting in more water efficient landscapes, but there are still some significant indoor efficiency potential.”
She pointed out that the figure on the right shows that the largest savings can be found through repairing leaks. “While not found at very high rates in all homes, there are some homes and businesses that have very high leak levels, and by reducing or eliminating those leaks, we can reduce per capita demand on average across the state by 11 gallons per person per day,” she said. She also noted that there are still a lot of old toilets in use, and the second largest potential for savings would be to install high efficient toilets that use only 1.28 gallons per flush.
“So by focusing in on particularly on leak repairs, toilets, clothes washers, some of these other categories, we’re able to get significant savings,” she said.
Agricultural efficiency potential
Agriculture is a major user of water in California. Ms. Cooley said that for this part of the analysis, they didn’t do any new studies but instead looked at studies that have already been completed.
“There are several studies that have looked at the technical potential for water savings in the agricultural sector,” she said. “There have been two studies conducted by CalFed, both in 2000 and in 2006 and more recently in 2009, the Pacific Institute did a study on the efficiency potential from agriculture. We found some pretty remarkable agreement in these estimates, ranging from 5.6 to 6.5 MAF per year.”
“Agricultural use is about 35 MAF per year but it can vary, so this represents around a 15 to 17% reduction in agricultural water demand,” she said. “Some of these savings represent reductions in consumptive use which can represent new water supply, but others represent savings in non-consumptive use.”
“I want to make a couple of points around the efficiency savings because I think there’s still a lot of confusion around this,” she said. “It’s fairly complicated, but I want to be clear that these efficiency savings represent demand reductions. Some of those savings represent additional supply that can be allocated to other use, but the rest mean less water taken from surface and groundwater with a number of benefits, such as less polluted runoff, instream flow augmentation, energy savings and reductions in GHG emissions, delays or eliminates need for capital-intensive infrastructure, and reduces vulnerability to drought and other water supply constraints.”
She then presented an infographic depicting the multiple benefits of water efficiency, noting that the figure on the left is a less efficient system and the figure on the right is a more efficient system. “In both cases, we’ve kept crop production at the same levels, but on the right, we’ve improved the application efficiency of water, therefore allowing less water withdrawals. We’ve also reduced non-beneficial losses, so there are some potential reductions in consumptive use and new water produced,” Ms. Cooley said.
She pointed out that on the less efficient left, there is a higher level of return flows, while the more efficient right side has lesser return flows. “If we compare and contrast these different figures, we can see on the right there are a number of very important differences from the figure on the left. I will note that in both cases, we maintained agricultural production – that is they are still producing the same amount, but on the right, we have reduced non-beneficial consumptive losses in effect creating new supply.”
“Also in the figure on the right, we also have less polluted runoff because we’re using water more efficiently, so we’re able to apply less fertilizer and therefore have less runoff into our rivers, streams, groundwater aquifers,” Ms. Cooley said. “We also have more water to support instream flows. In particular, if you compare the middle sections of the rivers, there’s also less energy for pumping, reducing or eliminating the need for expensive infrastructure to withdraw that water in the first place. We also have less vulnerability to drought, so there are a number of important benefits to reducing total water withdrawals.”
Water recycling and stormwater capture
Ms. Cooley said that there are significant opportunities to boost water reuse in California. She said the study considered water reuse quite broadly, including both onsite reuse such as gray water, as well as opportunities to boost recycled water, which is where wastewater is captured and conveyed to treatment facilities, treated and either redistributed or used to recharge groundwater.
“California has made some considerable improvements in recycled water over the last 40 years,” she said. “Looking back at 1970, we were recycling less than 200,000 acre-feet per year. By 2009-2010, we were up to around 670,000 acre-feet, so there was considerable improvement during that period. Of course, little known fact is that the single largest user of recycled water in California is the agricultural sector, but in addition to that, we are using recycled water for a variety of applications. We’re using it for groundwater recharge, urban irrigation, and even some commercial and industrial purposes. But there are some opportunities to further boost and increase the use of recycled water.”
“We find opportunities to increase water reuse by 1.2 to 1.8 MAF per year,” she said. “These are the potential savings after we’ve done all of the efficiency improvements, and I think that is something important to keep in mind, because as we improve indoor efficiency, that does mean that less water is available for water recycling. We did not double count that water, so what you’re seeing here is even after we’ve implemented significant and considerable efficiency improvements, we still have opportunities for water reuse and recycling.”
The NRDC took the lead on the analysis of the potential opportunities for stormwater capture, expanding on some of their earlier work, Ms. Cooley said. She noted that the study only looked at stormwater capture in the urbanized areas of Southern California and the Bay Area, although she acknowledged that there are some stormwater capture potential opportunities in other areas of the state as well.
“We find that there are opportunities to boost stormwater capture beyond current levels by 420,000 to 630,000 acre-feet per year,” she said. “This can take a variety of forms; it can be rainwater harvesting at a residence, or it can be at a municipal or community scale where we’re capturing stormwater and using it to recharge groundwater.”
She noted that it is based on current urbanized areas and doesn’t integrate climate change, or other variability. “If we do include those factors, it would likely even be higher,” she said.
So in summary …
“In summary, combining all these different strategies, we find that the potential water savings, that is reductions in withdrawals from our rivers and streams, is equivalent to about 10.8 to 13.7 MAF per year,” Ms. Cooley said. “These potentials strategies could be implemented in every region of the state, and in fact, to some degree they already are, so what we’re talking about is really increasing that implementation. In some regions, the urban efficiency improvements dominate, and in other regions, it’s agriculture but again there are opportunities across the state.”
Ms. Cooley then invited Kate Poole from the Natural Resources Defense Council to join her at the podium to answer questions.
Question: What do you find is the biggest challenge or obstacle to implementing those ag efficiency water savings?
“I think there are a lot of barriers,” said Ms. Cooley. “Some of it is the pricing policies that we use for water; some of it is that a lot of this requires some additional investment, and that may be investment that’s hard to come by. I think there are some challenges with our water rights system and how that’s implemented. I think that it’s important to note that agriculture is becoming more efficient with its water use – they are adopting drip irrigation, micro sprinklers, and they are doing irrigation scheduling, so we are seeing these changes. We could be doing a lot more and there’s a lot of different ways we could go about doing that.
“One specific place that is sometimes a hurdle is that farm managers might want to implement more efficient water delivery techniques, but they are not supported by the distribution infrastructure, which doesn’t support on demand delivery, so part of it is that we have to upgrade the distribution infrastructure to allow farmers to make these efficiency improvements,” added Ms. Poole.
Question: Could you elaborate more specifically on the techniques that would achieve those savings in agriculture?
Ms. Cooley replied, “There are a variety of strategies that could be implemented in agriculture. In the past, we’ve looked in particular at adopting drip and microsprinklers and other more efficient irrigation technologies; we looked at opportunities to implement irrigation scheduling, using weather and other scientific information, and soil moisture monitors, but it’s still something that’s not done universally. There are also some strategies such as deficit irrigation whereby you can stress the plant at certain drought tolerant stages for certain crops; there is potential savings there as well. There are opportunities to boost soil moisture holding capacity with organic matter in the soil that can also represent a water savings and efficiency improvement.”
For more information …
For copies of the reports, infographic, and fact sheet, visit: