You fill it with soap and water about 300 times a year, so it must be clean. Right? A case out of Germany, published by the American Society for Microbiology, says no.

After babies in a German hospital’s neonatal intensive care unit were found to have multidrug-resistant pathogens on their skin, inspectors went to work to find out why.

The incubators and health care workers all tested negative, but Klebsiella oxytoca kept appearing on the babies. “Klebsiella oxytoca is emerging as an important bacterial isolate causing hospital-acquired infection in adults and having multiple drug resistance to commonly used antibiotics,” the National Institutes of Health wrote.

The source of the bacteria was finally traced to the detergent drawer and rubber seal of the energy- efficient washer in the hospital’s laundry room. After the washing machine was removed, the contaminations stopped. They have not recurred.

The case report notes the domestic washing machine at the hospital was not part of the institution’s main laundry room. It was near the nursery for mothers to wash their clothes, and nurses used it to wash the knitted hats and socks they put on the babies.

Energy-efficient washers are designed to clean in water that is cold or warm, saving the consumer money. The Department of Energy even recommends using cold water to do your laundry whenever possible.

But, as CNN reports, studies have found the temperature needed for effectively killing possibly pathogenic bacteria is 140 degrees F or higher, which is considered hot water. As we’ve become more environmentally conscious, however, we’ve lowered the temperature of the water to save energy (and money). In Europe, for example, colored laundry is usually washed at temperatures between 86 and 104 degrees. In China, South Korea and Japan, cold water is preferred.

“When you do your towels with a cold-water wash, it’s hard to get them really clean because they’re so thick,” Dr. Charles Gerba, a microbiology professor at the University of Arizona, told CNN. “You’ve got to use hot-water wash and dry it really well.”

If you don’t, he said, “you’ll get more E. coli on your face when you dry it with a towel than if you stuck your head in a toilet and flushed.”