The Lemon Slice Method
Here's how it works: Cut two lemons into slices or wedges and place them inside your kettle. Fill the kettle about halfway with water and turn it on. Once the water boils, pour it out but keep the lemon pieces inside. Refill with fresh water halfway and boil again. After two cycles, your kettle should be noticeably cleaner. If not, repeat the process once or twice more.
