Can overnight boiled water be consumed? Is it harmful to the human body?

Generally, overnight boiled water that is properly stored can be safely consumed without significant health risks. However, improperly stored overnight water may pose potential health hazards. If any abnormalities occur, it is advisable to seek medical attention promptly. The detailed analysis is as follows:

Boiling water kills most microorganisms. If the boiled water is immediately sealed after cooling, stored in a clean container, and placed in a cool area or refrigerated, microbial growth will be minimal overnight. The water quality remains largely unchanged and is generally safe to drink, especially if consumed within a short period (e.g., within 12 hours).

If boiled water is left exposed to air for an extended period after cooling, or if the storage container is not thoroughly cleaned, dust and microorganisms from the air may enter the water and multiply rapidly. Additionally, repeatedly reheating overnight water may slightly increase nitrite levels (which normally remain within safe limits under proper storage, but risks increase with prolonged improper storage). Drinking such water may lead to gastrointestinal discomfort, such as bloating or diarrhea.

To safely store overnight boiled water, use a clean, sealed container and avoid leaving it open to the air. Re-boiling the water before consumption can further eliminate any potential microorganisms. If the water has been stored for more than 24 hours or develops an unusual odor or cloudiness, it should be discarded and not consumed.