Limescale is the chalky residue you might find on the inside of appliances that hold water such as coffeemakers, kettles and metal teapots. Over time, this residue can affect the taste of any beverage prepared in these vessels; it can also damage appliances, requiring you to replace them.
Fortunately, removing limescale is a fairly easy thing to do and usually doesn't require any special equipment. In fact, you probably have everything you need to descale your stainless steel teapot in your kitchen right now!
Wash out the inside of the teapot.
Fill the teapot two-thirds full of lemon juice or, if the limescale is really bad, white distilled vinegar, and then add water to top off the teapot.
Leave the teapot to sit for several hours. If the limescale is really bad, let it sit overnight.
Pour the lemon juice/water mixture out and use the toothbrush to scrub away stubborn limescale spots.
Rinse the teapot thoroughly to remove any odors from the lemon juice or vinegar.