That unsightly white, chalky substance in your kettle is called lime scale. It is a result of built-up calcium deposits that occur when water with high calcium levels evaporates, like when you boil water in your kettle. Although lime scale is not harmful, if you don't wash it out, it can build up and eventually clog your kettle's spout.
Fill the kettle with a half cup of white vinegar.
Add two cups of water.
Heat the kettle until the liquid boils. Let it boil for a few minutes.
Empty the kettle.
Rinse the kettle with fresh water. Repeat Steps 1 through 4 if any lime scale remains on the kettle.
Wash the kettle before you use it.