Environ. Sci. Technol. 2010, 44, 5601–5607
Life Cycle Environmental Implications of Residential Swimming Pools N I G E L F O R R E S T * ,† A N D E R I C W I L L I A M S †,‡ School of Sustainability and School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona
Received February 6, 2010. Revised manuscript received May 31, 2010. Accepted June 2, 2010.
Ownership of private swimming pools in the U.S. grew 2 to 4% per annum from 1997 to 2007. The environmental implications of pool ownership are analyzed by hybrid life cycle assessment (LCA) for nine U.S. cities. An operational model is constructed estimating consumption of chemicals, water, and energy for a typical residential pool. The model incorporates geographical climatic variations and upstream water and energy use from electricity and water supply networks. Results vary considerably by city: a factor of 5-6 for both water and energy use. Water use is driven by aridness and length of the swimming season, while energy use is mainly driven by length of the swimming season. Water and energy impacts of pools are significant, particularly in arid climates. In Phoenix for example pools account for 22% and 13% of a household’s electricity and water use, respectively. Measures to reduce water and energy use in pools such as optimizing the pump schedule and covering the pool in winter can realize greater savings than many common household efficiency improvements. Private versus community pools are also compared. Community pools in Phoenix use 60% less swimming pool water and energy per household than subdivisions without community pools.
1. Introduction Swimming pools are a common feature of many U.S. urban landscapes. Private pools are on the increase, growing at between 2% and 4% from 1996 to a total of 8.4 million in 2007 (1)- (2) (3), especially in warmer regions. While swimming pools certainly add to quality of life, it is also important to consider their environmental implications and how these could be better managed. One environmental issue is the effect of pools on water scarcity. For example, in the Southwest, a rapidly urbanizing region, a warmer climate is also an arid one, where previous studies have clearly determined that domestic properties with pools have markedly increased water consumption over those without (4). Extensive infrastructure in the forms of dams, canals, pumps, and pipes are needed to collect and transport water to areas where domestic supply is insufficient to meet demand. Supplying water entails environmental impacts both in terms affecting ecosystems where water is transported away from * Corresponding author phone: (480)242-5843; e-mail: nforrest@ asu.edu. † School of Sustainability. ‡ School of Sustainable Engineering and the Built Environment. 10.1021/es100422s
2010 American Chemical Society
Published on Web 06/16/2010
and in energy and other materials use in collecting and transporting water. Chemical use is another environmental impact. Maintaining water quality in pools requires substantial amounts of chlorine, acids, and other chemicals. The U.S. pool chemical market was valued at $1.2 billion in 2008 (5). Demand for commonly used compounds runs at around 150,000 tons for chloroisocyanurates (6), 80,000 tons for calcium hypochlorite (2, 7) and 70,000 tons for muriatic acid (8). These chemicals entail impacts in their manufacture, use, and final environmental fate. The connection between chlorine manufacturing and mercury emissions is wellknown (9), and residual chlorine in water effluent is known to have aquatic toxicity (10). Atmospheric emissions of chlorine from swimming pools have been correlated with urban ozone formation (11) and chemical inputs can alter regional hydrology by accumulation of dissolved solids in groundwater with consequential degradation of aquifers and soils (12). A third area of concern is energy. After space heating and cooling, pool pumps are often the next highest consuming appliances in households that have a pool (13). According to the 2001 residential end-use survey by the Energy Information Agency, pool pumps accounted for 0.9% of total U.S. residential electricity consumption in 2001 (3). A Natural Resource Defense Council report estimated energy consumption by pool pumps alone in 5 U.S. cities to range from 2000 to 4000 kWh per year per pool (14). To our knowledge there has been as yet no systematic analysis that endeavors to describe the full environmental implications of pools. In this article we construct a model based on hybrid life cycle assessment to estimate energy and water use and associated greenhouse gas emissions of a residential pool. We subsequently use the model to compare resource use and emissions for pools in 9 cities across the U.S. We also use the model to evaluate the potential water and energy savings from some simple mitigation measures applied in Phoenix, where we also compare pool related consumption of residential subdivisions with community pools against those without. The Phoenix metropolitan area (Maricopa County) is of particular interest because it is an area of rapid growth, where more than 26% of 1.08 million single family residential (SFR) properties in 2007 have a pool (15), and in which residential pool ownership, currently at 0.074 per capita, is growing faster than population (15) (16). But more than this, it is an area of hot, arid climate that relies on distant and nonrenewable sources for its water supply and may therefore be more vulnerable to negative effects from swimming pools than other areas.
2. Method The method used is hybrid life cycle assessment (LCA). There are three main LCA methods: process, economic input-output LCA (EIO-LCA), and hybrid LCA. We use the term “process” to denote the most common form of LCA as delineated by the International Standards Organization (17). This method is based on a bottom-up model of a supply chain, with each constituent process described in terms of material inputs and environmentally significant releases or outputs (18). One limitation of this method is that any process for which materials input output data are unavailable is excluded from the analysis, leading to truncation error (19). EIO-LCA, on the other hand, utilizes top-down macroeconomic models which describe a national economy via monetary transactions between sectors. Combined with sector-level environmental data, these models can be used to estimate total supply chain VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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impacts of production, though at a more aggregated level than process models (20), (21). The term hybrid LCA generically refers to any method combining process and economic input-output analysis. There are a number of hybrid approaches; the first is additive hybrid in which economic data are identified covering processes for which materials data are unavailable and associated with sectors in an EIO model (22). An economicbalance hybrid calculates the value-added covered in a materials process model, subtracts this from the total price, and estimates impacts associated with the remaining value using EIOLCA (23). A mixed-unit hybrid model constructs a matrix model with both physical and economic quantities (24). The current case study is suitable for the additive approach: due to the lack of publicly available data detailing materials flows for the production of pool chemicals we estimate this factor using price data for chemicals and EIOLCA. Illustrating for energy, the additive hybrid method is based on the formula ETotal ) Ep + EEIO
(i)
ETotal is the total embodied energy of a residential pool. EP is the embodied energy which can be estimated from process data, such as the electricity use in pool pumps and can be expressed as the sum of Epi, energy requirement of the ith procedure of manufacturing EP )
∑E
pi
(ii)
EEIO is the embodied energy from economic IO (EIO) LCA, which accounts for those components that have relevant economic data (cost, energy intensity, etc.). Let j be an index denoting sectors for which such economic data can be obtained, excluding processes already covered in the processsum piece, eq ii EEIO )
∑PE
SC j j
(iii)
Pj is the cost (for example, chemical cost in $/year), and ESCj is the energy intensity of relevant sector in MJ/$ obtained from the U.S. EIOLCA model developed by the Green Design Initiative at Carnegie Mellon (25). We define the functional unit of assessment as the pool year, representing the inputs, outputs, and impacts resulting from a standardized SFR swimming pool in one year. We introduce some notable limitations to the scope of the assessment. We consider only the operation and maintenance phase of the life cycle: pool construction, remodeling and end of life, pump and other equipment manufacture are ignored. We also ignore heating of pool water, use of pool covers, and final transport of pool chemicals to pools. Inventory analysis identifies and quantifies inputs and outputs to the system. In the absence of any convenient, publicly available data sources reliably reporting pool input and outputs, our approach is to construct a pool maintenance model from the critical parameters affecting inputs and outputs, and for which data are available. Using this model and parameter values representing a particular pool, input quantities are evaluated. The pool model is described in more detail below. The impact categories relevant to the goals of the study are resource depletion (specifically water), energy consumption, and global warming potential. Energy and water consumption is immediately obvious from the direct energy and water inputs. Less obvious, however, is the secondary consumption of these resources by the upstream, utility systems that deliver them. Using information from available literature, regional water intensity of electricity and electricity 5602
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intensity of water supplies is determined and used to calculate second order consumption of these resources. Global warming potential from regional energy consumption, of which nonelectrical energy is negligible, is calculated from state electricity consumption, generation and emissions data, and standard CO2 equivalence tables. The prime purpose of LCA is to inform decision makers of environmental impacts of products or processes to assist them to make the most appropriate choices. It is therefore important to analyze the uncertainty of LCA results (26), (27). Uncertainty due to variation in values of input parameters can be treated using Monte Carlo simulation (28). We model each input parameter and its uncertainty as a probability density function. We use Monte Carlo simulation to generate a sample of 5000 outcomes from which final results are presented as mean and standard deviation. In our simulation we assume all input parameters have Gaussian distributions and are independent. For each input we determine the mean and standard deviation either by a) calculation, when the data sample is large enough; b) calculating the mean and estimating the standard deviation as the sample range/2 when the sample is small and it appears to represent the most common range of values; c) by calculating the mean and estimating the standard deviation as the sample range/6 when the sample is small and it appears to represent the full range; and d) assuming a coefficient of variation of 0.05, 0.10, or 0.20 based on subjective assessment of the data quality, when there is only a single data point. We use the model to first compare results for a standard pool in nine cities across the U.S. and then to compare pool impacts per household in residential subdivisions with and without community pools. We use data collected from a wide range of publicly available pool operating guidelines and other miscellaneous literature to define what appear to be standard operating practices for pools in the U.S., the assumption being that pool owners generally follow the recommendations in these sources and others like them. For pool surface area we used the mean of pools in the Phoenix area (15) as our standard. For climate data we used mean monthly temperature, precipitation, and free water surface evaporation data (29), (30) specific to the location. Data on community pools and subdivisions were obtained by inspection of satellite images from 2005 using Google Earth (31).
3. The Pool System Model The pool system consists of the pool infrastructure, the pool contents, and processes that occur within the pool (Figure 1). The purpose of the system is to maintain a constant volume of clear, sanitary water. Due to the introduction of contaminants, through environmental processes and pool use, the sanitary condition and clarity of the water is continuously degraded. Water volume is affected by evaporation, precipitation, pool use, and maintenance. To maintain the ideal pool state, it is therefore necessary to regularly add water, sanitize the water, and remove unwanted substances. By modeling the water flux, pump schedule, and chemical application schedule of the pool system, inputs and emissions can be calculated. Model data inputs consist of pool system characteristics describing the physical attributes of the pool system, operational parameters that reflect the timing, duration and intensity of system processes, and climatic conditions specific to the pool location. Table 1 summarizes the model inputs that we use as a standard for comparing pool impacts in different cities. Within the model we refer to the closed season as the winter period when the pool is partly drained and covered in cold regions or maintained at a very low level in freeze free areas. The open season is when maintenance must be increased above the winter level. The
FIGURE 1. Schematic summary of the pool system showing inputs, outputs, and processes.
TABLE 1. Main Inputs to the Pool System Model Describing the Standard Pool Used for City Comparison and Typical Climatic Conditions for Phoenixg physical characteristicsd 2
pool area (feet ) pool depth (feet) pool level headroom (inch) winter level (inch)f pool pump (kW) pump flow rate (gpm)
mean
SD
442 5.0 4 -18 1.2 63
113 0.5 1 6 0.3 10
operational parametersd
mean
SD
pump summer (hours/day) pump winter (hours/day) backwash period (weeks) backwash duration (mins) refill period (years) trichlora dosec (oz) trichlor period (days) cal-hypob dose (oz) cal-hypo period summer (weeks) cal-hypo period winter (weeks)
9.2 4.8 2.5 3.5 6.0 1.4 1 14.6 2.5 4.0
1.8 1.0 0.5 0.9 1.3 0.2 0 3.2 0.5 0.4
environmental conditions (Phoenix)e
mean
SD
season length (days) rainfall (inches) evaporation (inches) winterize (yes/no)
191 8.0 65 no
21 0.8 6.5
a Trichloroisocyanuric acid. b Calcium hypochlorite. Chemical doses are per 10,000 gallons of water. d Standard values used for all cities. e Location specific values. f Distance below minimum operational water level. Applies only to winterized pools. g SD ) standard deviation. Details of data sources and estimates can be found in the Supporting Information. c
swimming season (for most people) occurs within, but is shorter than, the open season. The model is simplified in several respects. Of particular note, it is assumed that all sanitization is by direct chlorination via trichloroisocyanuric acid and calcium hypochlorite; auxiliary pool chemicals are ignored, the use of pool covers are ignored; and pool leaks and splash loss are ignored. These and other details are discussed in the Supporting Information.
4. Life Cycle Use of Water and Energy 4.1. First Order Inputs. First order water consumption (W1) is defined as the total water consumed from the main supply in one year and is calculated by summing monthly water consumption as in eq 1 W12 1 )
∑w
(1)
i
i)1
where wi is the water use in month i calculated as the input required to maintain the water level between a minimum and maximum level after adjustment for the total monthly flux (precipitation + evaporation + backflush + refill). Water added to the system is positive in sign, and water leaving the system is negative. When the water level falls below the minimum level it is replenished from the supply, and when it exceeds the maximum, water is discharged. Water level is carried over from one month to the next. In addition to evaporation, water is discharged from periodic backwash to clean filters and from less frequent discharge and refill to reduce dissolved solids or for winterization. Pools subject to freezing are winterized by draining all near surface pipes, reducing the water level below inlet levels and covering. First order electricity input (E1) is defined as electricity consumed within the pool system and is calculated by eq 2. In winterized pools, the system is completely shut down in the closed season, and thus pumping hours per day is zero. In nonwinterized pools, pumping is still required during the closed season but at lower levels than the open season E1 ) P[HoS + Hc(365 - S)]
(2)
where P is pump power (kW), Ho is pumping hours per day in the open season, Hc is pumping hours per day in the closed season, and S is the open season length in days. Chemical input quantity Cj for a chemical j is calculated by eq 3. No chemicals are applied in winterized pools during the closed season Cj ) Dj[Fj,oS + Fj,c(365 - S)]
(3)
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Details of model equations can be found in the Supporting Information. 4.2. Energy Use to Supply Water. First order water input results in additional electricity consumption E2 throughout the water supply network. Energy consumption of the water network can be broken down into processing stages of extraction/transport, treatment, distribution, and wastewater treatment. Within each stage the energy consumed varies due to physical and process differences, and the overall consumption of each network reflects the unique nature of its composition. Arpke and Hutzler (32) collated results from a number of isolated studies to construct an overall U.S. intensity of 1.2 to 5.4 kWh/1000 gallons. We use this aggregate U.S. range to calculate secondary energy consumption arising from first order water use for all locations except Phoenix and Los Angeles. For Phoenix we calculate a more specific result of 3.1 to 5.2 kWh/1000 gallons from a comparative local LCA study of different water sources (33) and the composition of residential supply from these sources in the Phoenix Active Management Area (PAMA) (34). For Los Angeles we use a value of 13.0 kWh/1000 gallons for Southern California obtained from a California Energy Commission report (35) and assume a coefficient of variation of 10%. Los Angeles’s water is particularly energy intensive because of its reliance on long distance transport systems, the State Water Project in particular. 4.3. Water Use to Supply Electricity. Secondary water consumption (W2) occurs from the generation of first order electricity used by the pool (E1). We use state level water consumed per unit power consumed (gallons/kWh) from thermal and hydro generation sources (36) in conjunction with the total generation from each of these sources in 2005 (37) to obtain a single intensity for each state. This is consumptive water use from evaporation, either from thermal plant cooling or from hydro reservoir surface. However, water consumption from hydro generation is first adjusted by a factor of 0.55 for multiuse economic allocation of hydro facilities as estimated for Arizona (38). Effects of water and electricity consumption, other than the second order electricity and water consumed, are ignored. For example, the materials and energy in the infrastructures, administrative overheads, or transport activities. 4.4. Energy Use To Produce Pool Chemicals. To obtain the energy use associated with pool chemicals, we use the EIOLCA model developed by Carnegie Mellon using the Benchmark U.S. input-output table for 2002 (25). Note that use of the model is based on the formula
FIGURE 2. Model results for a standard pool system in 9 different U.S. cities. (a) Annual water use (gallons) by process. (b) Annual energy use (kilowatt-hours) by source. (c) Annual carbon emissions (kilograms CO2 equivalents) by source. Error bars represent (1 standard deviation.
material use/emission ) sectoral supply chain use/ emission intensity (units/$) producer price
5. Results: Comparison of Pools in 9 U.S. Cities
One first chooses the appropriate sector among the 428 sectors in the 2002 model which produces the product of interest. The EIOLCA model generates the supply chain materials use/emission intensity of that sector. One then multiplies this intensity by the producer price of the product, which is the consumer price less wholesale, transport, and retail margins. Most, if not all, pool chemicals belong to NAICS industry sector 32518 (Other Basic Inorganic Manufacturing) for which the EIOLCA model reports 32 MJ energy consumed and 2 kg CO2 equivalent emitted per $ spent. The value of pool chemicals is estimated from the quantities of chemicals consumed and market prices of those chemicals. Prices are adjusted to 2002 to match the EIOLCA data model used. Publicly accessible price data for pool chemicals are scarce. A U.S. International Trade Commission report provides an aggregated 2002 price for trichlor and dichlor of $1.05 per lb (6). A 2002 producer price of $0.75 per lb for calcium hypochlorite was inferred from 1999 and 2003 prices (7, 39).
As shown in Figure 2, results for the standard pool in nine U.S. cities vary widely and are closely related to climatic conditions. More details are provided in the Supporting Information. Water consumption is highest by far in the hot arid climate of Arizona, closely followed by Southern California at 30,000 and 22,000 gallons, respectively. The only other city to exceed 10,000 gallons is San Antonio at almost 13,000 gallons where despite greater evaporation than Los Angeles (52 in. compared to 50), net consumption is much less due to higher rainfall (33 compared to 15 in.). With the exception of Tampa, all of the other cities (Atlanta, New York, Chicago, St. Louis, and Seattle) have relatively low water use because rain greatly compensates evaporation during the open season, and they are covered for the closed season. Consequently in these cities, the largest component of water consumption at 50 to 60% is the annual discharge and refill required for winterization. Although evaporative losses are the greatest component in Phoenix and Los Angeles at 52% and 42%, respectively, secondary water consumption from electricity generation is
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also high at 27% and 30%, respectively, reflecting relatively high hydro electric sources and dry climate in these states. Tampa, in comparison, has the lowest overall water use at approximately 6000 gallons, a result of annual net evaporation of zero, no large refill like the winterizing states, and low water consumption by Florida electricity generation. Energy consumption clearly divides the cities into winterizing and year-round groups with year-round cities typically consuming 3500 to 3900 kWh compared to 750 to 1800 kWh in winterizing cities. This bimodality is a result of year round pump operation in those cities that do not winterize. The remaining variation is mainly due to varying lengths of open season. In most cities, secondary energy consumption of the water supply is less than 3% of the total except in Los Angeles where it almost 6%. This is due to the high energy intensity of Southern California water (13 kWh/ 1000 gallons (35)), but it should be noted again that we use a U.S. average intensity for all other cities (except Phoenix). Energy from pool chemical consumption ranges from 11% to 14% of the total. Estimates of pool pump energy use in California of 2580 kWh and 3000 kWh reported in ref 14 agree well with our result of 2974 kWh for Los Angeles. If it can be assumed that the 1500 kWh reported by the Energy Information Administration (3) is for a winterized pool, then it also agrees well with our results. Energy consumption results are discussed in more detailed in the Supporting Information. Greenhouse gas emissions results follow a pattern similar to energy consumption but with St. Louis being notably higher and Los Angeles lower in relative terms than they were for energy due to the above and below average GHG emission rates for Missouri (0.94 kg CO2 equivalent/MWh) and California (0.27 kg CO2 equivalent/MWh), respectively (37).
6. Mitigation: Phoenix Case Study Numerous measures exist that can reduce consumption and emissions of individual pools including use of pool covers, more efficient pumps and pool design, reduced pumping schedule, monolayer evaporative barriers, and more attentive maintenance. These measures are available to pool owners today and their take-up may be accelerated by the introduction of standards, building codes, and local ordinances (Supporting Information). Urban planning may also play a role by, for example, favoring community pools in residential subdivisions over individual private pools. Using the model, we estimate the potential savings in first order household energy and water consumption from three simple mitigation measures and compare to some common household efficiency actions (Table 2). We select Phoenix as a case study for this exercise as it has the highest overall impacts, which we estimated at 13% of the average Phoenix household water consumption, 22% of electricity use, and 20% of greenhouse gas emissions (Supporting Information). Recommended pool pumping schedules range from 6 to 12 h per day, loosely based on the time required to circulate the pool volume once. However, it is not clear that this either achieves the objective of circulating all pool water through the filter or that this objective is even necessary. What is necessary is to keep the pool clean and to maintain uniform free available chlorine between 1 and 3 ppm. Empirical evidence from a Florida Atlantic University study of 120 Florida pools (in ref 40) suggests that circulation time can be reduced to less than 3 h per day without adverse results. Simply reducing pump operation in warm climate zones, an action that costs nothing, can save more electricity than upgrading a 2007 national stock central air conditioning unit to a high efficiency unit at a cost of several thousand dollars. Pools in warm climate zones free of winter freezing risk are generally kept open all year round. A low level of maintenance is necessary over the winter although the pool
TABLE 2. Estimated Phoenix Area Annual First Order Household Energy and Water Savings from Pool Impact Mitigation Measures Compared to Common Household Efficiency Upgradesd action reduced pump schedule (3-5 h summer, 2-3 h winter) warm climate winterization (cover pool and extend winter by 1 month) community poola low flow shower headsb efficient clothes washer efficient dishwasher low flush toilets (3 to 1.3 gal/flush) eliminate leaky plumbing and fixtures. efficient refrigerator (642 to 450 kWh annually) efficient central air conditioning (11.6 to 18 SEER) efficient lighting (switch all incandescent bulbs to compact fluorescent)
water (gallons) energy (kWh) 1720 5870
1330
6730 2650 4630 280 9740
920 27 25
5200 300 1420c 1270
a Savings for community pool action are the mean of per household savings calculated for 9 Phoenix subdivisions. b These appliances also have energy savings. c Household efficiency savings estimates are based on US averages with the exception of central air condition which is based on warm climate zone use. d Sources: see the Supporting Information for more details.
is generally not used in this period (ignoring heated pools). Covering the pool over the winter eliminates the need for maintenance. Obviously covering a pool all year round, except when in use, is even more preferable. We posit that inconvenience is the major reason for the low incidence of pool cover use (Supporting Information), but this only applies during swimming season. It is also apparent that maintenance needs to be increased above the relatively dormant winter level earlier in the year than swimming commonly begins and continues for some time after swimming ends. Extending the period that the pool is covered up to the start and end of the swimming season can further increase the benefit of warm climate winterization. This action in warm, arid climate areas is low cost and can save more water per year than upgrading to a high efficiency clothes washer and 4 times as much energy as upgrading to a high efficiency refrigerator with no loss of utility. Community pools in residential subdivisions provide an alternative to backyard pools while retaining much of the utility. We investigated how the presence of a community pool affects the incidence of backyard pools and aggregate resource use per household across a sample of nine Phoenix area residential subdivisions. The mean backyard pool occurrence was 0.05 per house in subdivisions with a community pool compared to 0.44 per house in adjacent subdivisions without. The mean subdivision aggregate resource use per household was calculated to be 1770 gallons of water and 327 kWh electricity in the community pool subdivision (site use only, excluding upstream resource use) compared to 8500 gallons and 1240 kWh in adjacent subdivisions.
7. Discussion Pools clearly have substantial resource use and emissions, but results are strongly influenced by climate. Florida, California, and New York for example, all have approximately VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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0.04 pools per capita (1) (41), but their water, energy, and greenhouse gas emissions are starkly different. Local conditions are therefore important when assessing the impact of pools. Areas of highest water and/or energy consumption (Los Angeles, Phoenix, Tampa) are also areas of high pool concentration where climate is the common driver behind pool resource use, demand for pools, and population growth. We only looked at a small selection of possible mitigation measures but found that savings in these high impact areas are not hard to come by. At the individual household level, simply covering the pool during winter or reducing the pumping schedule offer potential savings comparable to or exceeding that of commonly accepted household efficiency improvements. At the neighborhood scale, we found that a planning policy favoring community pools in residential subdivision over backyard pools can yield substantial reductions in the mean household water and energy use compared to neighboring subdivisions without community pools equivalent to upgrading every house in the subdivision to high efficiency clothes washer and refrigerator, low flow shower heads, and compact fluorescent lights.
Acknowledgments This research was sponsored in part by the grant “Sustainable infrastructures for energy and water supply” (#0836046) from the National Science Foundation, Division of Emerging Frontiers in Research and Innovation (EFRI), Resilient and Sustainable Infrastructures (RESIN) program. We thank William Kennedy of P.K. Data Inc. for permission to use data and Yvonne Plascencia of Maricopa County Assessor’s Office for providing data.
Supporting Information Available Phoenix area demographic and pool trend data, data and notes on pool model input parameters and input/output calculations, notes on pool model and limitations, Monte Carlo simulation and outcomes, chemical use result, pump energy result, data and calculations for water supply energy use and electricity supply water use, results table for cities and for community pool subdivisions, mitigation and policy measures, and calculations for pool and household appliance savings estimates. This material is available free of charge via the Internet at http://pubs.acs.org.
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