The potential water saving of low-flow fixtures as documented by the Albuquerque single-family homes case study
The need for new and innovative solutions to urban water scarcity may be no more apparent than in New Mexico’s largest city, Albuquerque. Residing along the Rio Grande River, the city has grown and thrived despite the water resource limitations characteristic of its semi-arid climate. The current residential population of approximately 507,000 and the commercial, industrial, and institutional sectors these residents support continue to persist in large part because of their reliance on the city’s once highly productive underlying aquifer. However, due to years of unsustainable pumping rates, the aquifer is experiencing significant drawdown and has caused subsidence in some areas, highlighting the reality of Albuquerque’s water scarcity challenges and the need for new and innovative adaptation strategies (Gutzler and Nims 2005).
Since Albuquerque can no longer exclusively rely on groundwater to meet municipal demand, it is now placing its bets on a water rights deal reached in the ’60s by water managers who recognized the imminent need for another source of water and secured a portion of the upper Colorado River (Hall 2005). As a result, in 2008 Albuquerque will begin using 90% surface water (diverted from the San Juan Basin and channeled 26 miles under the Continental Divide) and 10% groundwater (City of Albuquerque 2005; Stomp 2006). To be sure, this is a large-scale, complex, and expensive innovative solution to Albuquerque’s water supply challenges. Unfortunately, though, as we advance into the 21st century, we are all faced with the new water supply challenges inherent in drought, climate change, and population growth.
Drought has always occurred in the US, and always with some degree of variability. Climate modeling efforts, however, are now predicting that there is a high likelihood that climactic changes, along with above-average temperatures, will enhance the historic variability, thus generating more extreme drought events (New Mexico Office of the State Engineer 2006). So what does this mean for water supplies?
Smaller winter snowpack accumulation with an earlier and faster spring snowmelt—coupled with more intense but possibly less frequent rainfall events—will likely impact reservoir flood control release regimes. The result: The volumes needed to meet peak summer demands may no longer be available. Higher temperatures are expected to enhance water supply risks by increasing sublimation, evapotranspiration, and soil dryness and decreasing stream flows (New Mexico Office of the State Engineer 2006).
Adding to the water supply challenges is population growth. This variable alone may pose challenges beyond the capacity of many US regions’ water supplies. As urban populations increase, so will the demand for potable water and the energy required to provide, treat, and heat it.
For Albuquerque, these factors pose considerable 21st-century water security risks. The city’s new San Juan–Chama project may not be able to sufficiently meet the needs of a growing population. The source of Albuquerque’s new surface-water supply is a diversion from the upper San Juan Basin, where the water resource impacts of drought and climate change are likely to reduce snowpack, runoff, and surface flows (Saunders and Maxwell 2005). These conditions possibly would not pose too great a challenge if there weren’t so many competing uses of surface flow (and connected groundwater) in the San Juan Basin and the greater Colorado River Basin. However, there are competing demands for the source of Albuquerque’s new surface-water supply, and the city may be forced to share shortages (US Fish and Wildlife Service 2005). Therefore, there are no guarantees that the city will always have access to its full diversionary water right in the coming decades, possibly forcing a return to groundwater dependence.
What Can Be Done?
While Albuquerque’s water supply future may appear grim, there are adaptive measures that can be adopted to empower the Albuquerque Bernalillo County Water Utility Authority (ABCWUA) and its customers to manage water shortages. There are water resource managers in the state of New Mexico who understand the need to engage in a comprehensive statewide urban (and agriculture) water-conservation planning effort. This plan would identify and remove barriers to conservation by clearly defining and mandating by statute the state and local government and water purveyor roles in designing and implementing programs (Funk 2007).
Comprehensive statewide and even watershed-level planning are important topics that are likely to receive much more attention in the near future. This study’s analyses highlight the benefits of innovative adaptation strategies, which are expected to be included in a broader, more comprehensive approach to coping with water resource challenges of drought, climate change, and population growth. One category of innovative adaptation strategies discussed in the Albuquerque case study, water conservation, or using water more efficiently, holds the potential to generate significant opportunities for coping with these challenges.
Using Water More Efficiently
Currently available and newly emerging technologies offer the potential to decrease total water demands by increasing efficient water use by end users, without negatively impacting the quality of life. Two innovations that meet these criteria were examined in Albuquerque. The first innovation, the (often) high-efficiency dual-flush toilet, enables end users to use considerably less potable water for flushing. The second innovation, the Shower Water Conservation System, makes it possible for users to not only use potable water more efficiently but also use heated water more efficiently. Possibly the most attractive feature of these two innovations is that they do not require significant behavioral changes for their benefits to be realized. That is, end users can continue to use the toilet or shower with the same frequency and/or duration as they normally do and still save water and energy resources and save money. Moreover, greater efficiency at the end-user level translates into resource and monetary benefits at the water utility level.
The dual-flush toilet and Shower Water Conservation System’s potential benefits were estimated using a four-step process. According to Gleick et al. (2003), “The first step in evaluating the savings potential of water conservation options is to establish a reliable baseline of current water use patterns.” Therefore, the first step this study took was to estimate the Albuquerque single-family home baseline (or status quo) “per capita” toilet and shower water and energy demands and costs. This initial analysis exposed new and valuable information regarding the city’s household indoor water-use patterns. That is, because of the combined effectiveness of the 1992 Energy Policy Act flush volume standards for toilets bought and sold in the US, and the ABCWUA toilet rebate program, Albuquerque single-family homes’ current per-capita shower water demand exceeds that of current per-capita toilet water demand. This new information, while contrary to what earlier studies’ findings may have estimated almost a decade ago, provides insight into what type of targeted conservation strategies may be appropriate for ABCWUA household customers today.
The second step involved estimating the “per capita” toilet water and energy demand reductions and avoided costs under four different scenarios of single-family home dual-flush toilet and Shower Water Conservation System usage. Third, this study generated ABCWUA single-family home population projections to estimate the toilet and shower water and energy demands and costs to the year 2030. Finally, the potential water, energy, and monetary benefits from using the aforementioned innovations were estimated over the same 24-year time horizon. These benefits are discussed in terms of generating an alternative water supply to meet current and future demand, reducing demands on electricity production and natural gas, thus demonstrating their ability to enhance water and energy security.
The Dual-Flush Toilet
The dual-flush toilet offers significant resource and monetary benefits by presenting the user with the option of two flush volumes. That is, with each flushing event the user can choose between two flush volume buttons, 1.6 gallons per flush for solid waste and 0.8 gallon per flush for liquid waste. To determine the potential benefits, the baseline single-family home per-capita toilet water demand was first estimated between 1994 and 2030.
The toilet water demand plot in Figure 2 tells an interesting story. The 1992 National Energy Policy Act was implemented in 1994, requiring toilet models bought and sold in the US to be 1.6 gallons per flush. Prior to then, toilet models were designed to use either 6.0 or 3.5 gallons per flush (Gleick et al. 2003). Two years later, the ABCWUA implemented its toilet rebate program, offering its customers a rebate as an incentive to replace their older, less efficient toilet model with a 1.6-gallon-per-flush model (Yuhas 2005). In 2001, Western Resource Advocates performed a study estimating Albuquerque single-family homes had reduced their water use from 183 gallons per person per day (in 1994) to 135 gallons per person per day (Western Resource Advocates 2003). Looking a little to the future, this study estimates that by 2011 ABCWUA single-family home customers will no longer be using older 6.0- or 3.5-gallon-per-flush toilets. Beyond 2011, even though homes are only using 1.6-gallon-per-flush models, population growth is relentless with regard to its impact on total per-capita toilet water demand.
Plotting the aforementioned baseline, or status quo, toilet water demand alongside this study’s most conservative retrofit scenario, where each year 60% of ABCWUA single-family homes are using dual-flush toilets and 40% are using a mix of 6.0-, 3.5-, or 1.6-gallon-per-flush toilet models, demonstrates the potential water supply benefits. Clearly, there is a volumetric difference in total water demand between the two plots. Possibly less clear are the slopes of these lines, which are also different.
The difference between these two plots highlights the amplified water savings associated with using the dual-flush toilet over time. That is, this study estimates a savings of 629 acre-feet in 2011, 687 acre-feet in 2020, and 745 acre-feet in 2030. Each year, these significant volumes of alternative water supply may be used to meet current growing demands or stored to meet future demands.
Increasing the efficiency of toilet water use also impacts energy demands. At the ABCWUA’s facilities both electricity and natural gas are required to pump water, treat water to drinking-water standards, and treat wastewater. Thus, using the aforementioned status quo toilet water demand estimates, similar status quo and 60% retrofit scenario benefits were estimated for the electricity and natural gas demands of toilet water.
Again the plots’ differing slopes highlight the benefits associated with using the dual-flush toilet over time. This study estimates an electricity demand reduction of 842 megawatt-hours in 2011, 919 megawatt-hours in 2020, and 998 megawatt-hours in 2030. Under this scenario, every year offers the potential of a larger demand reduction as population increases and a consistent 60% of single-family homes use the dual-flush toilet.
To begin to understand what these electricity savings may represent, it is helpful to know how much electricity a megawatt-hour is in terms of household demand. In 2005, Albuquerque single-family homes consumed an average of 7.09 megawatt-hours per home (Power New Mexico 2006a). Thus, the electricity demand reductions revealed in this study are significant.
As with electricity, dual-flush toilets offer the potential to reduce natural gas demands, since it is consumed in some of ABCWUA’s pumping and wastewater treatment. Under the same 60% retrofit scenario, this study finds that natural gas savings are 13,841 Therms in 2011, 15,115 Therms in 2020, and 16,405 Therms in 2030. To put these savings in perspective, Albuquerque single-family homes used an average of 664 Therms per home in 2005 (Power New Mexico 2006a). The volumes of natural gas saved each year may be used to meet other demands or stored to meet future ones.
The Shower Water Conservation System
The Shower Water Conservation System is a newly emerging innovation designed exclusively by (and US Utility Patent Application Pending status held by) this report’s author, Andrew Funk. The potential water saving benefits of this innovation are not as substantial as those associated with using dual-flush toilets. However, since this innovation enables end users to not only use water more efficiently but also use heated water more efficiently, the potential for energy savings gets much more interesting.
Essentially, the Shower Water Conservation System eliminates the unnecessary water and energy waste normally lost down the drain, while individuals wait for the water to reach an acceptable temperature before stepping into the shower. One important feature that separates this system from hot water on demand and hot water recalculating systems is that it functions completely independent of an energy source. The system’s main function is to collect cold/lukewarm water before it flows from the showerhead (or faucet) and to slowly re-inject it back into the hot water stream flow during showering.
As the hot water valve is opened, the initial water temperature may be anywhere from 40°F to 120°F or higher. The average preferred showering temperature, though, is 105°F (Gleick et al. 2003). Thus, depending on the plumbing between the shower and the water heater, a significant volume of previously heated water is normally discarded down the drain while waiting for the preferred water temperature. This study estimates that a typical three-person single-family home loses over 1,400 gallons down the drain annually waiting for hot water from the water heater to reach the showerhead. The Shower Water Conservation System eliminates this unnecessary wasting of water and energy resources in the following way.
When cold/lukewarm water flows through the thermostat, the valve is open and the water is directed to the two reservoirs. When the water reaches 105°F, the thermostat closes and hot water is then redirected toward the showerhead. On its way there it flows through a Venturi. The Venturi’s narrow section is connected to the reservoirs via a one-way check valve. Since pressure is at its least in the Venturi’s narrow section, the stored cold/lukewarm water, with a greater force as a result of gravity and some suction, is injected into the hot stream flow. Here the heat energy of the hot water stream flow thermodynamically reheats and absorbs the cold/lukewarm water. Throughout the shower event the cold/lukewarm water is injected at a rate that has a negligible impact on the shower water temperature. Therefore, individual showering events may occur without wasting the initial (previously heated) cold/lukewarm water and the energy resources consumed for potable treatment, delivery, and end-use water heating and wastewater treatment.
As with the toilet analysis, the Albuquerque single-family home total per-capita shower water demand was estimated and compared to four different retrofit scenarios. The comparison with this study’s (more conservative) 60% retrofit scenario assumes that 60% of ABCWUA single-family home customers are using the system and 40% are not. Since shower water demands eventually increase over time as population increases, it is important to consider new and innovative solutions that increase efficiency of each showering event.
This study finds that the water saving benefits of the Shower Water Conservation System translate into 291 acre-feet in 2011, 318 acre-feet in 2020, and 344 acre-feet in 2030 of alternative water supply that may be either used to meet current demand each year or stored to meet future years’ demands.
Since this system enhances efficient use of heated water with each showering event, the total electricity and natural gas demand reductions extend beyond those that occur upstream or downstream at the water utility for pumping, drinking-water treatment, and wastewater treatment. Moreover, heating water is highly energy intensive, so the estimates under this study’s 60% retrofit scenario, even though conservative, are noteworthy.
This study estimates that the combined ABCWUA and single-family home electricity demand–reducing potential under the scenario in Figure 8 is 6,606 megawatt-hours in 2011, 7,214 megawatt-hours in 2020, and 7,829 megawatt-hours in 2030. These significant reductions are eight times the electricity demand–reducing potential offered by single-family homes using dual-flush toilets. These reductions lead to fewer demands on thermoelectric power generation and thus lead to less greenhouse gas emissions.
When one considers that about 60% of US households use natural gas water heaters to heat their shower water, it is clear that any innovation that increases hot-water-use efficiency is mutually beneficial to both the water utility and its customers (Wendt, Baskin, and Dufree 2004). Here, the combined ABCWUA and single-family home natural gas savings are estimated at 0.50 million Therms in 2011, 0.55 million Therms in 2020, and 0.59 million Therms in 2030. These savings are 36 times the estimated potential natural gas savings when single-family homes use dual-flush toilets, thus decreasing demand and potentially contributing to fossil fuel and greenhouse gas reduction goals.
Benefits Generate Opportunity
The water-use efficiency estimates presented above demonstrate that there are significant volumes of alternative water supply and energy resource savings possible with current and emerging innovations. But what do those benefits translate into? The answer is opportunity. As Albuquerque (and the US) advances into the 21stcentury, where the ability to meet demands will become increasingly difficult under pressures of drought, climate change, and population growth, it may be possible to maintain a more sustainable water and energy demand, while at the same time acquiring an alternative water supply, thus enhancing water and energy security.
Looking to the 60% retrofit scenarios presented above and assuming a new scenario where 60% of ABCWUA single-family homes are using the dual-flush toilet and the Shower Water Conservation System, the opportunities generated are substantial. This study found that from 2008 through 2012 the water saved is enough to meet the annual demand of about 11,461 homes.
Currently 46% of Albuquerque’s electricity is generated by coal, largely from the closed loop cooling system at the San Juan generating station in the upper Colorado River Basin. Moreover, about 740 gallons of water are used (some of it consumptively) for every megawatt-hour of electricity generated (Power New Mexico 2006a; Power New Mexico 2006b). So, the resultant electricity demand reductions are enough to decrease the volume of water withdrawn from the Colorado River system by 45 acre-feet (Power New Mexico 2006a). Equally important, the electricity demand reductions represent the same amount of electricity annually consumed by 6,107 Albuquerque homes. The natural gas savings generated are enough to meet the annual demand of 3,685 single-family homes.
Continuing with the same aforementioned 60% retrofit scenario and five-year period, the homes using these two innovations collectively save an estimated $7,535,440 (in 2006 dollars, r = 5%). This is money that would likely contribute to other local economies. The ABCWUA would also enjoy monetary benefits of about $299,000. These funds may be used to further improve water conservation programs or other programs that collectively may enable Albuquerque to meet the water resource challenges of drought, climate change, and population growth.
Quantifying the monetary benefits from both water and energy savings, this study emphasizes that new and creative conservation programs, especially those that purchase innovations in bulk (keeping the cost per unit low) and distribute them to homes for free, are highly cost-effective. In addition, distribution programs (rather than rebates) are more likely to produce the level of customer participation necessary to meet demand reduction goals more quickly. External to effective demand reduction policy then is that it is likely water-use efficiency will offset the need for developing or transferring more traditional supplies over long distances, which are often highly energy intensive (US Department of Energy 2006).
The Take-Home Message
Water saving innovations, along with creative retrofit policies, offer the ABCWUA and its customers the opportunity to maintain an alternative water supply to meet current and future demand as well as adapt to cope with the challenges of drought, climate change, and population growth. As with the greater US, Albuquerque’s current water supply is likely to face shortages in the near future as a result of water supply impacts associated with climactic changes and a growing demand. However, the types of innovative solutions examined in this report (and many others) demonstrate a large potential for mitigating adverse impacts to supply.
Current high-efficiency toilets such as the dual-flush toilet offer the water utility and its customers significant savings beyond the status quo water and energy-use reductions experienced since implementation of the 1992 Energy Policy Act and rebate programs. The savings translate into an alternative water supply and energy savings that may be used to meet current and future demand. Moreover, both the ABCWUA and its single-family home customers save money.
The Shower Water Conservation System is a newly emerging innovation that also facilitates water savings. However, since it saves hot (or previously heated) water used in each showering event, considerably more energy resources are conserved. Again the alternative water supply and (to a greater degree) avoided energy consumption offer the opportunity to meet current and future demands, while simultaneously saving money and reducing greenhouse gas emissions.
This research demonstrates that there is power in efficient water-use innovations beyond mere water conservation. Water purveyors that do not recognize that power are designing conservation policies under incomplete information. Using water-efficient innovations, as part of a comprehensive planning effort, may enable cities to cost-effectively enhance water and energy security in the 21stcentury. Therefore, it is important that water purveyors understand and take full advantage of the potential benefits associated with existing and newly emerging innovative solutions to water and energy supply challenges.
Aldo Leopold said, “Conservation is a positive exercise of skill and insight” (1949). The message readers should gather from this summary and its larger parent study is the following: If 21st-century water resource managers understand and take full advantage of the types of insights presented in this study and skillfully exploit them within the context of a larger, more comprehensive approach to enhancing water and energy security, then future generations may be more resilient and empowered to cope with the water supply challenges inherent in drought, climate change, and population growth.
Note
This article is a summary of a professional project report by Andrew Funk, submitted in partial fulfillment of the requirements for the degree of master of water resources at the University of New Mexico. This report was approved by the following graduate committee: Professor of Economics Janie Chermak (co-chair), Professor of Environmental and Water Resources Engineering Julia Coonrod (co-chair), and Anne Watkins, special assistant to the New Mexico state engineer.
The research presented in this article evaluates the potential of innovations, as well as begins to enhance the understanding of their role in 21st-century comprehensive planning. This research, which used the city of Albuquerque as a case study, reflects the findings of Andrew Funk’s graduate research at the University of New Mexico’s Water Resource Program. The breadth of these findings may be downloaded at https://repository.unm.edu/dspace/handle/1928/2589. Note: This material has been copyrighted by the author, and this research material was presented by the author at the Southwest Hydrological Society conference in August 2007.