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Cool water as effective as hot for removing germs

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Cool water removes the same amount of harmful bacteria as hot, according to small study on handwashing.

The issue of water temperature has been debated for a number of years without enough science to provide proof that water temperature makes a difference in hand hygiene, said the US researchers.

“This study shows us that the temperature of the water used didn’t matter”

Donald Schaffner

In their study, published in the Journal of Food Protection, high levels of a harmless bacteria – A non-pathogenic strain of Escherichia coli – were put on the hands of 21 participants multiple times over a six-month period.

They were asked to wash their hands in 60-degree, 79-degree or 100-degree water temperatures using 0.5 ml, 1 ml or 2 ml volumes of soap.

Water temperature as high as 38°C and as low as 15°C did not have a significant effect on the reduction of bacteria during hand washing, said the researchers.

In addition, they found an antimicrobial soap formulation (1% chloroxylenol) was not significantly more effective than the bland soap for removing E. coli under a variety of test conditions

Senior study author Dr Donald Schaffner said: “People need to feel comfortable when they are washing their hands but as far as effectiveness, this study shows us that the temperature of the water used didn’t matter.



“Also we learned even washing for 10 seconds significantly removed bacteria from the hands,” said Dr Schaffner, from Rutgers University in New Jersey.

While the study indicated no difference between the amount of soap used, he called for more work to understand exactly how much and what type of soap was needed to remove harmful microbes.

However, he added that the latest findings had implications for guidelines and energy use.

“This study may have significant implications towards water energy, since using cold water saves more energy than warm or hot water,” he said.

“Instead of having a temperature requirement, the policy should only say that comfortable or warm water needs to be delivered,” he said. “We are wasting energy to heat water to a level that is not necessary.”

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