In the arid western US, securing reliable and cost-effective energy and water resources has always been a limiting factor for development. In California, saving water has become a collective challenge as the state faces one of its toughest droughts yet. On February 28, 2009, Governor Arnold Schwarzenegger challenged California residents to use 20% less water in their homes as part of his plan to improve the Sacramento–San Joaquin Delta. With the wide range of technological options available to achieve this goal through efficiency gains, how can California (and other places looking to cut water consumption) maximize resource conservation?
One way to think about maximizing the benefits of water conservation is to look beyond water savings. What the governor and water users around the state may not realize is that saving water will also save another valuable resource: energy. Maximizing energy and water co-benefits is also the best way to maximize limited (and ever-shrinking) financial resources, but unfortunately most water conservation measures are evaluated on the basis of cost-effectiveness for water savings alone.
Water delivery and treatment services use energy during their entire life cycles. For example, water is pumped from its place of origin to a city and later transported from people’s homes to a wastewater treatment plant. Transportation energy requirements of water vary greatly depending on the distance traveled. The amount of energy used to deliver water from northern California to residential customers in southern California, for example, is equivalent to approximately one-third of the total average household electric use in the region (Cohen et al. 2004). California’s State Water Project is the single largest user of electricity in the state (Wilkinson 2000), and up to 56% of an average city’s energy use can go toward pumping and treating its water supplies (California Energy Commission 1992). And California is not alone. In every state and every community, energy and water are inextricably linked.
Once at its point of use, water may be used indoors or for landscape and other outdoor uses. Water used indoors is often heated or cooled, using more energy. Extensive amounts of energy are required for heating water—44% of natural gas used within the home goes toward heating water (California Public Utilities Commission 2008). Outdoor water use is the least energy consumptive, as it is rarely heated or cooled, and often infiltrates, evaporates, or runs off, avoiding the need to pump it to a treatment plant. Replacing standard showerheads with highly efficient ones can save energy in the same way that replacing incandescent light bulbs with compact florescent light bulbs does.
The goal of our study was to develop simulation models that could predict and optimize the energy co-benefits of residential water conservation measures, help us prioritize technologies, and evaluate water conservation policy proposals. We used data from Santa Clara Valley Water District (SCVWD), Metropolitan Water District of Southern California (MWD), and East Bay Municipal Utility District (Figure 1) to calculate the total cost savings of water efficiency technologies and impact of water conservation policy proposals. Combined, these three water districts serve nearly 22 million residents in California. For each water saving technology (showerheads, faucets, toilets, etc.), we used best available water use values. In each district, we used existing saturation rates (the number of households currently using each technology) and calculated the cost savings at full saturation. The models allowed us to compare the cost effectiveness of water efficiency technologies when only water savings are considered with the cost effectiveness of water efficiency technologies when energy and water savings are both considered.
Calculating the energy co-benefits of water conservation requires a better understanding of what the co-benefits are, but it is also important to understand how they relate to policy making: what the obstacles and opportunities are for achieving them. It is not always clear how current or future policies may encourage or discourage these investments, what the potential for co-benefits is, and how technology advances can be evaluated through the lens of co-benefits. A second part of our study evaluated whether existing water conservation policy proposals in California will also result in energy savings.
Ranking Water Efficiency Technologies by Energy Saving Potential
Our analysis shows that investment in water efficient technologies should be made in the following order to maximize energy savings: showerheads, faucet aerators, ultra-low-flow (ULF) toilets, high-efficiency (HET) toilets, drip irrigation, shut off devices activated by rainfall, clothes washers, pool covers, irrigation controllers, soil moisture probes, efficient dishwashers, and, lastly, composting toilets (Table 1). This rank order highlights the change in cost-effective evaluation that comes from a co-benefits perspective. Showerheads cost more money per acre-foot of water conserved than faucet aerators, but are prioritized for investment. This is due to the greater combined energy and water savings that can be achieved by reducing indoor water use, particularly when the water consumed is heated.
Our results provide quantitative support for the maxim that conserving indoor water is better, but we also show that conserving heated indoor water is best. Showerheads and faucet aerators are the first technologies that should be invested in due to their low cost per acre-foot and their use of indoor heated water. Toilet fixtures that utilize unheated indoor water are the next technologies invested in, followed by all the outdoor water technologies. However, efficient clothes washers and dishwashers rank much lower in the order of investment table, due to their relatively high cost per acre-foot saved.
When does investment in these technologies save money? Figure 2 shows a side-by-side comparison of the cost of moving to full saturation of each of the water efficiency technologies in the MET. When the lines are below zero, savings occurs. As the graph shows, when considering Total Resource Cost (the cost that account for all of the resources saved besides water) all indoor water efficiency technologies have costs that are less than zero: They save money. These results are consistent across all three of our study sites.
Policy Impacts
To evaluate whether existing water conservation policy proposals in California will also result in energy savings we developed four policy scenarios based on existing proposals in California. These four scenarios are a 20% per capita reduction in water use by 2020, an appliance focus for conservation, a mandate to increase conservation in new home construction, and a landscape irrigation focus for conservation.
Scenario 1: 20% Per Capita Reduction in Water Use. In 2008, Schwarzenegger urged legislators to support a 20% per capita water use reduction in California. While this target was not specific to the urban sector, the California Building Standards Code has been updated to also reflect a 20% reduction of indoor potable water use. The reduction outlined in the Code will be based on the maximum allowable water use per plumbing fixture and fittings as required by the California Building Standards Code.
In our analysis, the 20% by 2020 scenario for water is largely achieved through conventional inexpensive flow restrictors on residential fixtures as opposed to appliance or landscape efficiency measures. The target water savings of 20% is feasible through maximum saturation of 2.5-gpm showerhead, 2.5-gpm faucets, and minimal adoption of 1.28-gpf high-efficiency toilets.
Scenario 2: Appliance Focus for Conservation. The new California Building
Standards Code calls for clothes washers to have a maximum “Water Factor” that will reduce their use of water by 10% below California Energy Commission standards. In our analysis, we calculate the energy co-benefits of these standards if mandated by a water district for new and existing homes. This includes maximum saturation of water efficient dishwasher and clothes washers in both single-family and multi-family structures. The assumed flow ratings for dishwashers to be 3.5 gallons per load and clothes washers to be 27 gallons per load, more stringent than the California Building Standards Code, and to reflect the more efficient technologies available on the market.
Scenario 3: Comprehensive Plan in New Construction. East Bay Municipal Utility District (EBMUD) has a successful water conservation program that was estimated to save more than 100 million gallons of water per year among 1.35 million customers. Since 1994, the program has helped the district conserve 21 MGD, around one-tenth of current demand. We calculated the energy-water co-benefits that would result from water districts adopting a similar comprehensive program to new construction.
Specifically, the fixtures in the program analyzed by the mode were required to operate at the following levels of water use:
Toilet- 1.6 gallons per flush
Showerheads- 2.5 gallons per minute
Faucets- 2.5 gallons per minute
Dishwashers- 3.5 gallons per load
Clothes washer- 27 gallons per load
Pool Covers- 100% covered
Landscaping- Max drip irrigation, Evapotranspiration (ET) controllers
Scenario 4: Landscape Focus. The Water Conservation in Landscaping Act (AB 1881) was passed in 2006 to implement many of the CUWCC Landscape Task Force recommendations. AB 1881 requires DWR to update the Model Local Water Efficient Landscape Ordinance, based on Task Force recommendations, by January 1, 2009. This will then be adopted by local agencies by January 1, 2010. The bill also requires the Energy Commission to adopt performance standards and labeling requirements for landscape irrigation equipment, including irrigation controllers, moisture sensors, emission devices, and valves to reduce consumption of energy and water. The landscape scenario results presented in Table 2 assume maximum feasible investment in drip irrigation systems, ET controllers, moisture sensors, and shut off devices activated by rainfall.
The results of the scenario analyses are shown in Table 2. The 20% per capita reduction scenarios is cost-effective when total resources are considered in (including the embedded energy costs for transportation and treatment of water) in all three service areas. Savings are always greatest for MWD in all cases, due to the longer distance water travels to reach its point of use and despite the typically higher program costs in the area. The Appliance Focus and New Construction policy scenarios are only cost-effective for MWD. The Landscape Focus scenario is not cost effective for any of the three districts, and further reflects our emphasis on indoor water savings to maximize energy co-benefits.
What are the options?
Integrating policy measures across sectors is always a challenge, and one that is common in natural resources management. An example of the missed opportunity that comes from the current institutional design in California can be seen in recent events surrounding water management. With the recent drought and continuing ecosystem decline in the Sacramento Delta, focus has again been placed on California’s water use and how it can be modified to meet the state’s needs in the future. In highly developed areas like California, “it is now increasingly difficult to build major new water supply systems because of both environmental and economic constraints. As a result, there is growing interest in exploring options on the other side of the equation—the demand side” (Gleick 1998). Between 2001 and 2004, over $50 million has been invested by the state in urban water conservation programs (CALFED 2006).
With the growing focus on efficient appliances and technologies, it may seem that there is little room left for further gains from efficiency measures. However, our results show that even with existing market saturation of efficiency technologies, an average of 45% reduction in per capita residential usage is still possible in California with existing technologies. A full 20% of this reduction in residential water and energy usage will pay for itself through full market saturation of 1.5 gpm showerheads and faucet aerators. When the total resource cost was included, a 40% reduction in resource use became cost-effective, using a mix of technologies. Further, our findings consistently show that policy measures and technology investments that maximize energy and water savings should focus on indoor water use first.
One of the greatest barriers to achieving the maximum potential resource conservation through technology implementation is the isolation of water and energy conservation programs. A report by the California Energy Commission urges the state to “...develop and expand best practices and existing programs to realize the substantial incremental benefits of joint water and energy resources and infrastructure management” (Klein, Krebs, et al. 2005). One easy way to do this would be to allow for joint rebate programs for clothes washers and dishwashers between energy and water utilities. Our study found that high-efficiency clothes washers and dishwashers have some of the greatest energy and water co-benefits, but are currently some of the least cost-effective investments. Pooling the resources of both water and energy utilities for rebate programs could help close this gap.
Our findings also reinforce the fact that distance maters. Of our three study sites, MWD clearly transports water the furthest and consistently realized the greatest energy co-benefits from water conservation matters. We also found that current market saturation rates make a difference: The more room there is for technology adoption in a community or water service area, the more cost-effective investments will be.
Efficient water fixtures and appliances don’t just save water, they save energy. Water conservation specialists are doing more than saving water by increasing the market saturation of efficient water devices, and the way we evaluate cost-effectiveness of conservation programs should reflect these benefits.