Boiling water can kill bacteria and remove harmful substances to the human body. Because tap water is treated with chlorine, chlorine interacts with residual organic matter in the water, forming toxic and carcinogenic compounds such as halogenated hydrocarbons and chloroform.
When the water temperature reaches 90°C, the content of halogenated hydrocarbons rises to 191 micrograms/liter, and chloroform rises to 177 micrograms/liter, both exceeding the national standard by 2 times. When the water just reaches 100°C, the contents of halogenated hydrocarbons and chloroform are 110 micrograms per liter and 99 micrograms per liter, respectively. If boiled for another 3 minutes, these two substances quickly drop to 9.2 micrograms per liter and 8.3 micrograms per liter, respectively, meeting the drinking standard. Therefore, the best practice for boiling water is to let it boil for about 3 minutes.
Some people, in order to save water, often reheat leftover boiled water, which is a bad habit. Repeatedly boiling water can cause the water to "age," not only causing the loss of beneficial minerals for the human body but also possibly producing certain harmful substances such as nitrites. Once a large amount of nitrites enters the human body, it can cause red blood cells in the blood to lose their function of carrying oxygen, leading to tissue hypoxia. People who drink this water for a long time may experience symptoms such as nausea, vomiting, headache, bluish nails and lips, and palpitations. In severe cases, it can cause hypoxia and may even induce cancer.
Drinking a glass of cooled boiled water after getting up in the morning is beneficial to health. Many people like to prepare a glass of boiled water the night before and drink it the next morning. This practice is acceptable when the temperature is not too high. However, in summer, when the temperature exceeds 30°C and the air humidity is high, bacteria multiply rapidly, and overnight cooled boiled water will lose its biological activity and is easily contaminated, causing diarrhea. You can pour a small half-cup of boiled water the night before, cover it, and then mix it with boiling water to make warm water in the morning.
In addition, cooled boiled water should not be left for too long. It is best to finish the boiled water on the same day it was boiled. It is best not to drink cooled boiled water that has been left for more than 3 days.