Many people say that overnight water is toxic, mainly because of the "nitrite substance" in boiling water. Drinking water does contain a certain amount of nitrosamine compounds, because they are "drinking water disinfection by-products", but this "amount" is very small and is not worth mentioning at all.

Although boiled water has been stored for a long time, its "water essence" has not changed, and the content of microorganisms such as bacteria may increase, but it will not produce "harmful substances". As long as you can cover the cup and avoid being polluted by dust and impurities, it is no problem to store it overnight.

Barreled purified water stored for a long time and heated for a long time will indeed increase the content of nitrite in water. However, based on the bottled water of 18.9L, it takes about 20 barrels of water at a time to reach the level of poisoning.

The bottled water is relatively sealed and can be drunk for a long time.

Any substance should reach a "dose" when it is harmful or toxic, and so should nitrosamines. Please make it clear that nitrosamines can cause cancer only if they absorb 100-200mg per kg of body weight.