What are the harms of boiling water twice?

Under normal circumstances, reboiling water may lead to nitrite poisoning or temporary diarrhea and bloating. The specific analysis is as follows:

1. Nitrite Poisoning

Water that has been boiled multiple times, also known as "thousand-boiled water," undergoes repeated heating, which can result in the formation of large amounts of nitrites. Consuming such water may negatively affect health. If consumed in excessive amounts at once, it may lead to nitrite poisoning, causing symptoms such as general weakness, dizziness, nausea, and vomiting.

2. Temporary Diarrhea and Bloating

Frequently drinking reboiled water in daily life may adversely affect health. Long-term consumption could disrupt gastrointestinal function, leading to temporary symptoms such as diarrhea and bloating. It may even impair overall gastrointestinal health, potentially contributing to various illnesses. Therefore, it is advisable to avoid drinking reboiled water in daily life.

In addition, it is important to avoid repeatedly reheating water and to refrain from eating leftover food from the previous day to prevent potential harm to health.