There are two possibilities. The first is scale, and the solution is 1 You can pour some hot vinegar into the bottle, cover it tightly, shake it gently, leave it for half an hour, and then rinse it with clear water to remove the scale. ? 2. Add 50 grams of baking soda and a glass of water to the bottle, cover it tightly, gently shake it, let it stand for half an hour, and then wash it with water. ? 3. Break the egg shell into a water bottle, then pour a few drops of detergent and a proper amount of water, cover it, shake it up and down, and finally rinse it with water. The second possibility is that the glass on the outer wall of the water bottle has peeled off, because the hot water bottle is double-layered, so it should not be a heat insulation coating. It may be that the glass on the outer wall of the kettle has peeled off because it has been in the tank for a long time. In that case, you'd better change the inner container.