2013 Issue

57 w ater and energy are linked at our households more than we think. When we show- er, turn on the sink, or wash clothes, both water and energy flowwith the energy flowing to heat up the water. This linkage between water and energy has inspired researchers and utility man- agers to closely look at collaborative efforts to conserve the two resources in one action. More importantly, managers want to know which water conservation action can save the most energy. Although the linkage sounds easy to understand for an individual household, it gets more complicated when we look at multiple households across a city and throughout the country. This is because household water-use behaviors, appli- ances, demographic, and other factors vary significantly among households. In addition, households have different water heaters, which are set at different tem- peratures. Further, households also receive cold water from their municipal provider at various temperatures and they have differ- ent preferences for the temperature they wash their clothes with or take showers at. So how can we represent household water and energy linkages with all these varia- tions? And how can we determine which water conservation actions will save the most water and energy? To answer these questions, we drew on large water and energy datasets to statistically represent the range and likelihood of behavioral and technical variations among U.S. house- holds in toilet, shower, faucet, dishwasher, and clothes-washer uses. These datasets comprised 1.4 million separate water-use events in 400 households across 11 U.S. cities. The energy dataset contained 709 different water heater models, cold water intake temperature from 74 U.S. cities, and heater thermostat temperature data from 343 plumbing/heating firms in the U.S. We then sampled from the statistical distributions and combined the sampled values to estimate water and energy uses for each appliance in 50,000 hypothetical U.S. households. Our results show that, on average, households use 86 KWh of energy for every 1,000 gallons of water used indoors. Dishwashers use the most energy per gallon of water while showers and faucets follow. The toilet uses the least amount of energy per gallon of water as it only uses cold water. We also found that the results were heavily skewed: 15% of households use about one third of the total water and energy. In examining the results, we also found that water heater thermostat temperature and sink flowrate are the most important fac- tors that influence household energy-use. Therefore, turning down the water heater thermostat temperature and installing high-efficient faucets are themost effective actions to reduce household energy-use. These findings can help water and energy utilities identify collaborative efforts to effectively save both water and energy. Adel M. Abdallah came to Utah to attend Utah State University and work at the Utah Water Research Laboratory with Dr. David Rosenberg. He earned his Master’s degree and is now pursuing his PhD in water management hydroinformatics. His research is part of a multi-state and multi-institution research project to enhance regional capacity for water resource planning andmanagement. As a follow-up to his Master’s thesis research, he is now developing a city-wide model that will include the energy required to extract, treat, and distribute water to households. The city model will identify a cost-effective collection of water and energy conservation actions a city can implement to meet its water and energy conservation targets. Saving Water to Save Energy, and Saving Energy to Save Water A Quantitative Analysis For further details, you can download a copy of Abdallah’s thesis at http://digitalcommons.usu.edu/etd/1313/ , or e-mail him at amabdallah@aggiemail.usu.edu. By Adel M. Abdallah