If you have a kettle with a removable lid, start by taking it off and scrubbing away any built-up residue on the inside of the kettle. Then, fill the kettle with equal parts water and vinegar, and let it soak for 30 minutes. After that, empty the kettle and rinse it out thoroughly with hot water. If your kettle doesn't have a removable lid, simply fill it with equal parts water and vinegar, and let it soak for 30 minutes before emptying and rinsing it out. Either way, be sure to give your kettle a good scrubbing at least once a week to prevent any buildup of gunk or bacteria.