How long can boiling water be kept for?

　　Boiling water can kill bacteria and remove substances harmful to the human body. Because tap water has been chlorinated, chlorine interacts with residual organic matter in the water to form toxic carcinogenic compounds such as halogenated hydrocarbons and chloroform.

　　When the water temperature reaches 90°C, the content of halogenated hydrocarbons rises to 191 μg/L, and that of chloroform rises to 177 μg/L, both exceeding the national standard by 2 times; when the water temperature just reaches 100°C, the contents of halogenated hydrocarbons and chloroform are 110 μg/L and 99 μg/L respectively; if boiling continues for 3 minutes, these two substances rapidly drop to 9.2 μg/L and 8.3 μg/L respectively, reaching drinking standards. Therefore, it is best to boil water for about 3 minutes.

　　In order to save water, some people often reheat leftover boiled water. This is a bad habit. Because repeatedly boiling water will cause the water to age, it will not only lose the minerals that are beneficial to the human body, but may also produce certain harmful substances such as nitrite. Once a large amount of nitrite enters the human body, it can cause the red blood cells in the blood to lose the function of carrying oxygen, causing tissue hypoxia. People who drink this water for a long time will experience symptoms such as nausea, vomiting, headache, purple nails and lips, palpitation, etc. In severe cases, it can also cause hypoxia, and may even induce cancer。

　　It is beneficial to drink a cup of cold water after getting up in the morning healthy . Many people like to dry a glass of boiling water the night before and drink it early the next morning. This method is okay when the temperature is not high; for example, in summer, when the temperature exceeds 30 degrees Celsius, the air humidity is high, and bacteria multiply quickly, the water boiled overnight will lose its biological activity and be easily contaminated and cause diarrhea . You can pour half a cup of boiled water the night before, then close the lid, and drink the boiled water into warm water the next morning.

　　In addition, cold boiled water should not be left for too long. It is best to drink the boiled water that is boiled on the same day. It is best not to drink cold boiled water if it has been left for more than 3 days.