I see dark spots in my electric kettle interior. Is the water still drinkable?

The dark spots are likely caused by calcium and other minerals in the water. People who live in regions with high calcium content tap water (hard water) would often find mottling discolorations in their kettle. Please rest assured that the product is safe to use and the water is safe to drink. You can remove this discoloration by filling the kettle with one part vinegar to three parts water and bring the mixture to a boil. Then take it off the heat and let it cool to the touch before discarding the mixture.