Should my housemate stop warming her mug and returning the water to the kettle?

Brent and Amy have been friends for 15 years and lived together for seven in cold Ohio. Both drink a lot of coffee, and each warms their mugs before pouring in coffee. Brent wakes earlier and recently discovered that Amy heats her mug with boiling water from the shared kettle and then pours that water back into it.

He finds the practice gross, likening it to double-dipping or spitting wine back into the bottle, and worries about secondhand water after he once found a hair in his mug. Amy says pouring the water away is wasteful and that her mug is clean; she pours boiling water into the mug and back into the kettle, with no cross-contamination.

She argues that boiling kills germs and that the hair Brent found could have come from anywhere. After a moment’s doubt, she has mostly stuck to her routine but offered to use up her recycled water before Brent returns from work. Brent has looked into whether repeatedly boiling water affects quality and prefers not to have reboiled water for his pour-over and cafetière coffee.

United States, Ohio

reboiled water, kettle hygiene, mug warming, cross contamination, boiling water, secondhand water, pour-over, cafetière, double-dipping, shared kettle