Is it safe to drink water from a thermos the next day?

It's generally not recommended to drink water from a thermos after two days.

The main function of a thermos is to keep water warm, but over time, the number of microorganisms in boiled water gradually increases. If the thermos is not properly sealed, it can easily breed large amounts of bacteria and microorganisms. Long-term consumption of this water can easily lead to various diseases. Especially for minors, drinking stale boiled water can affect metabolism and growth; for the elderly, it can accelerate aging and increase the risk of stomach and esophageal cancer.

Therefore, to ensure good health, it is recommended to drink fresh water daily and avoid drinking water that has been left out for too long. If boiled water in a thermos needs to be stored, it's best to ensure the thermos is well-sealed and consume it within two days. If the water has been left for more than two days, it's best not to drink it for health reasons.

Furthermore, it's worth noting that not only water from thermoses, but also boiled water in other containers should not be stored for extended periods. For example, the optimal drinking time for opened bottled water is within one day, and the maximum drinking time for opened bottled water is no more than 15 days. Cooled boiled water should ideally be consumed within 16 hours of being stored in an uncovered cup, and no longer than 24 hours. These measures are to ensure the hygiene and safety of the drinking water.