"The water boiled repeatedly (thousands of boiled water) will become very unhealthy and not drinkable, because the content of nitrite increases greatly". This common sense of life is so popular that it has even been written in middle school textbooks. Some media have also made big fuss about it, pointing directly at the electric water heaters used by many enterprises, institutions and households. Ingestion of large amounts of nitrite will cause acute poisoning, and long-term ingestion of small amounts may cause cancer risk. Such serious consequences can''t help but worry.

　　But is this really the case?

　　First let us know a few basic facts. Nitrite will not be produced out of thin air. It is usually converted from the original nitrate in water under certain conditions. There are few nitrates in qualified drinking water, but if the water source is contaminated with nitrogen-containing organic substances (so-called eutrophication), the nitrate content will increase greatly. On this basis, there are mainly three possible sources of nitrite increase in drinking water: first, the evaporative concentration of repeated boiling water, the concentration of nitrite increases (but the total amount does not increase); second, the boiling water is placed longer Contaminated by bacteria during time, bacteria reduce nitrate to nitrite (but this is obviously not related to repeated boiling); its trinitrate is decomposed into nitrite and oxygen by heating energy (but only certain types of nitrate can be heated Decomposition, others cannot).

　　 Therefore, experts have always been cautious about the fact that "Thousand Rolling Water" contains a large amount of nitrite and is not drinkable. I personally doubt that water can only be boiled a few times, but not boiled for more than a few times.

　　Experts not only carried out meticulous analysis, but also provided terrible test data: Someone boiled the water 10 times and found that the content of nitrate was unchanged, and nitrite was not detected; there were still people Continuously use the water dispenser to repeatedly heat the barreled water. After heating to 181 times, the content of nitrite ions in the water is about 5 times that of the beginning.

　　 "5 times"?! You must not think this is a big number. At this time, the nitrite content in the water is only 3.53 μg/L. Although this figure exceeds the hygienic standard of bottled water (2 μg/l), it is still very safe. It does not cause acute poisoning, nor does it border cancer. Because the qualified ham sausage contains 30,000 micrograms (0.03 grams) of nitrite per kilogram (1 liter of water is also 1 kilogram), which is mainly used for color development and antisepsis. Moreover, who would really boil the water 181 times?

　　 Therefore, the argument that "Thousand Boiling Water" contains a large amount of nitrite and is not drinkable can be put to rest. Analyzed the other reasons about "Thousands of water can''t drink", and those reasons are also untenable. All in all, in his words, "Even the common sense of life in the middle school textbooks should not be taken lightly, it is almost impossible to encounter in daily life. Boiling water a few times will not cause any harm to the body" .

　　However, it is worth reminding that the boiling water is placed in a thermos pot (warm pot) for a long time, after 5, 6 (under the action of bacteria, plus the higher nitrate content in some rural areas) nitrite The content may increase significantly. Although I have no data, I have seen cases of nitrite poisoning (intestinal cyanosis) in infants caused by the use of this kind of water to prepare milk powder.