That hard to remove residue that forms on coffeepots due to hard water and daily use can be removed by dropping a few pennies inside the pot along with 2 tablespoons of white vinegar. Let this sit for a few minutes then swirl (gently for glass vessels) around before dumping. Rinse with boiling water. The acetic acid in the vinegar will dissolve the residue while the pennies’ edges scrape it away.