Generally, boiling water should not be used for three days in a thermos bottle. Because it is placed for a long time, the bacteria will produce nitrite after mass reproduction. If the body consumes too much nitrite, it will produce symptoms such as hypoxia and nausea, and it is easy to induce cancer. Of course, the premise is a large intake. If you accidentally drink it once, it will not cause great harm. If you accumulate a large amount, it will affect your health. It is recommended that you do not drink it repeatedly. It also contains a lot of nitrite.