INDIANA UNIVERSITY SCHOOL OF PUBLIC AND ENVIRONMENTAL AFFAIRS
By Shahzeen Z. Attari
In a national online survey, 1,020 participants reported their perceptions of water use for household activities. When asked for the most effective strategy they could implement to conserve water in their lives, or what other Americans could do, most participants mentioned curtailment (e.g., taking shorter showers, turning off the water while brushing teeth) rather than efficiency improvements (e.g., replacing toilets, retrofitting washers). This contrasts with expert recommendations. Additionally, some participants are more likely to list curtailment actions for themselves, but list efficiency actions for other Americans. For a sample of 17 activities, participants underestimated water use by a factor of 2 on average, with large underestimates for high water-use activities. An additional ranking task showed poor discrimination of low vs. high embodied water content in food products. High numeracy scores, older age, and male sex were associated with more accurate perceptions of water use. Overall, perception of water use is more accurate than the perception of energy consumption and savings previously reported. Well-designed efforts to improve public understanding of household water use could pay large dividends for behavioral adaptation to temporary or long-term decreases in availability of fresh water.
Fresh water is used increasingly beyond sustainable levels (1). Do people know how much water is used by a variety of daily activities? If people were asked to conserve water, would they know which behaviors are more effective than others? Gleick (2) estimated that 13.2 gallons of clean water are required per person per day for human needs (drinking, sanitation, hygiene, and food preparation). In 2005, the average American used about 98 gallons of water per day (3), of which ∼70% was used indoors (4). Thus, the average American uses more than seven times the water estimated by Gleick as needed. To understand how water use is distributed among daily activities in American households, Mayer et al. (5) surveyed 12 study sites during 1996 through 1998 to disaggregate residential end-use water consumption. Fig. 1 shows the average distribution for six categories. They also found that indoor water use was fairly homogenous across the 12 sites, except for the category “leaks”; whereas outdoor water use varies substantially depending on local climate (5).
Most Americans assume that water supply is both reliable and plentiful. However, research has shown that with climate change, water supply will become more variable due to salinization of ground water and increased variability in precipitation (6, 7). Some have argued that rather than focusing on increasing freshwater supply alone, we need also to reduce water demand (8). Demand-side policy responses to future freshwater variability will benefit from a deeper understanding of public perceptions of water use, which is the focus of this study.
Similar to Attari et al. (9), a study that explored public perceptions of energy use, here actual water use is compared with perceived water use for a variety of indoor and outdoor activities. Perceived energy consumption is a fairly flat function of actual consumption. Such a compression bias (9, 10) could result from participants’ lack of knowledge about energy in its different manifestations. The flatness is also partly due to the judgment heuristic of anchoring and insufficient adjustment (11, 12), which arises when a person generates a numerical estimate by first adopting a salient reference as a starting point and then adjusts this estimate in the desired direction, but insufficiently. Attari et al. (9) also showed that participants overestimate energy consumption for activities that use small amounts of energy, and underestimate consumption for activities that use large amounts.
Do similar over- and underestimations exist for judgments of water use? Given the consistent tangible physical quality that exists for water but is somewhat obscure for energy as well as the familiarity of the unit of measurement, one could expect more accurate estimates for water. Additionally, Attari et al. (9) found that both numeracy and pro-environmental attitudes are associated with more accurate perceptions of energy use. Similar predictions for individual difference variables are tested here for judgments of water use.
Perception of the “Most Effective Thing.” The study began with two open-ended survey questions that asked participants to indicate the most effective thing they could personally do to conserve water in their lives, and to indicate the most effective thing Americans can do to conserve water in their lives. These two questions were shown in randomized order, where 515 participants completed the order self/Americans and 505 participants completed the opposite order Americans/self. Two judges identified 25 mutually exclusive categories in a set of initial 50 surveys and then independently coded the remaining surveys (Table 1). Interrater agreement was “almost perfect,” κ = 0.86 (13).
Each of the 25 categories was then classified as a curtailment action (e.g., taking shorter showers) or efficiency action (e.g., switching to water-efficient fixtures). Some responses were difficult to categorize as curtailment or efficiency (e.g., checking for leaks and repairing them). Similar to the findings for energy use (9), where most participants mentioned curtailment over efficiency, here, 75.8% of participants mention curtailment actions for themselves and 67.4% for other Americans, and only 9.7% of participants mention efficiency actions for themselves and 12.5% for other Americans. By contrast, the Environmental Protection Agency (EPA) recommends that retrofitting toilets results in the greatest savings (71%) in indoor household water use (14), followed by retrofitting clothes washers (19%), showerheads (5%), and faucet aerators (5%). (Even though toilets use less water volumetrically than washers and showers per use, the frequency of use results in higher water use overall.) Note that a more subtle classification of the categories would be to code them as “intent-oriented” or “impact-oriented” behaviors (15). In intent-oriented behaviors, the intention to help the environment shapes the behavior without taking the actual environmental impact or effectiveness into account, such as turning off the water while brushing teeth. Alternatively, impact-oriented behaviors are focused on making a large difference, such as retrofitting toilets. The gap between intent- and impact-oriented actions may be explained by the lack of information (people do not know what is effective) or the lack of motivation (people are not motivated to act out effective behaviors). However, further research is needed to clearly classify the elicited behaviors in this manner.
About the Indiana University School of Public and Environmental Affairs
“Indiana University’s School of Public and Environmental Affairs was created to address complex issues in public policy and environmental science. Faculty are diverse and committed to high quality research; the winner of the 2009 Nobel Prize in Economic Sciences, Dr. Elinor Ostrom, is a professor at the School. Research is funded from multiple sources, such as the World Bank, the Environmental Protection Agency, the National Institutes of Health, the National Science Foundation, and the National Endowment for the Arts.”