Distilled water is water that has been boiled to become steam and then cooled to become water again. It's then free of minerals and salts. Distilled water is used in car batteries and in steam irons. Distilled water prevents the iron from getting clogged up inside from minerals. It also has various medical and industrial uses. Some people like to use distilled water to make clear ice cubes. Here's how to make distilled water in your kitchen.