Boiling water kills most pathogens, but once the water cools and is left out for an extended period, it can become a breeding ground for bacteria. If the boiled water was stored in a clean, sealed container, it’s less likely to be contaminated, but the risk increases significantly once exposed to open air.

Additionally, factors such as room temperature and exposure to sunlight can affect the growth of microorganisms in the water. It's generally safer to drink boiled water that has been cooled and stored properly within a shorter timeframe—ideally within a few hours. Therefore, due to the uncertainty of safety after 24 hours, it's recommended to exercise caution.