Descale your kettle with vinegar
Hard water contains dissolved calcium hydrogencarbonate, which breaks down into insoluble calcium carbonate, also known as limescale, when it’s heated. To get rid of it, mix one part vinegar or lemon juice with three parts water and boil the kettle, then let the hot mixture sit overnight. The acid will react with the limescale, forming soluble calcium salts that can be tipped away in the morning.