Amanda Carrico, the lead author on the paper, surveyed 510 people about their hand washing techniques and then estimated how much energy they were using. Most people—64 percent in the study—prefer to use hot water when washing. When you multiply that by the eight billion times Americans wash their hands each year, and how much energy it takes to heat that water, you wind up with a surprising amount of energy—0.1 percent of the total annual emissions of the United States.
People think that using hot water to wash their hands is more hygienic, but Carrico says that's not really true. “Although the perception that hot water is more hygienic is based in some factual evidence ... there are few, if any, hygienic benefits of using warm or hot water to wash one’s hands," she writes. The amount of heat required to kill bacteria is far higher than what your hands can withstand. So next time you're washing, turn down the heat.
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