Plain old tapwater can be dangerous. Water heaters set too high send thousands (mostly children) to hospitals each year with burns. Most safety experts recommend a setting of 120 degrees F. But finding that setting on the dial isn't easy—most dials aren't labeled with numbers. If the stickers on the water heater don't tell you how to set the temperature and you can't find the owner's manual, use this method: Run hot water at the tap closest to the water heater for at least three minutes. Then fill a glass and check the temperature. If the water is above 120 degrees, adjust the dial, wait about three hours and check again. Repeat until you get 120-degree water. For a final test, check the temperature the following morning, before anyone uses hot water.
Be safe—keep the dial at 120 degrees F