You'd better not drink it. Many health care programs I have watched say they are harmful to human body. Generally speaking, the content of nitrite in this water will be higher. A large amount of nitrite can directly poison people, because nitrite reacts with human blood to produce methemoglobin, which makes blood lose its oxygen-carrying function and makes people suffer from hypoxia poisoning.

Although the content of nitrite in repeatedly boiled water is not so high, when nitrite reaches a certain dose in human body, it has carcinogenic, teratogenic and mutagenic effects, which can seriously endanger human health. Therefore, try not to boil water repeatedly. It is also best to "burn hot water as you drink it" in the water dispenser, and don't keep it in a state of "heating-insulation" all the time.