First of all, it is actually incorrect to repeatedly circulate the problem that water burning is harmful on the Internet. There is a little knowledge in high school chemistry that repeated boiling water will lead to an increase in nitrite, which will cause cancer and teratogenesis. However, there is not enough experimental evidence to show that repeated boiling of boiling water will lead to an increase in nitrite. No matter how water (H2O) burns, it is still water. If the nitrate in water increases, it can only be reduced to nitrite, but the reduction of nitrate to nitrite is a chemical reaction, and heating with boiling water alone will not contribute to this reaction. In addition, according to the law of conservation of mass, if water burns for a long time, it will evaporate water (H2O), but other salts and metal ions in it will not change, which is only a physical change. According to a paper entitled "Influence of Repeated Boiling of Drinking Water on Water Quality" published in Environmental Science and Technology in May of 20 1 1, it shows that repeated boiling of water has little influence on water quality.

The results of this experimental study are as follows:

1. The tap water meeting the national standard was boiled repeatedly, and no nitrite was detected. Even if a certain amount of nitrite is artificially added, the quality of nitrite will not improve with the increase of boiling times, and repeated boiling of water on the surface will not cause the improvement of nitrite.

2. Other water quality indicators also meet the national water quality standards and will not pose a threat to human health.

For the other three conclusions, please refer to the experimental research journal. In addition, Fang's "Can I Drink Repeatedly Boiled Water" published in "Public Health" and "Junior High School Students' Heaven and Earth" also has a detailed statement. Boiling boiled water several times will not harm your health.

Secondly, the problem of boiling soup for a long time is the same as the repeated boiling of water. The longer the soup is cooked, the more water will evaporate and the concentration of the soup will increase. Other salts and metal ions will not change except the volatilization of organic matter.