Hard water is water that contains calcium or magnesium mineral ions often in the form of carbonate. These ions do not pose any health threat, but they can engage in reactions that leave insoluble mineral deposits. Hard water mineral deposits, or scaling, is the precipitation of minerals which form limescale. How to Descale? 1. Fill the kettle with 1 cup of vinegar or lemon juice and 2 cups of water. 2. Boiling the liquids and leave it for 2 hours, then use cloth to clean and wipe. 3. Rinse the kettle with clean water, and dry with a soft, clean cloth. 4. Repeat as needed. Note: Its normal if your kettle exposes spot or rust on the stainless steel bottom after the first use, if the water quality in your area is so hard.