Water can be drunk overnight, but many people think it is not. They think that there are many harmful substances in the water overnight, because some chemical reactions have taken place in the water overnight, producing more harmful substances, even carcinogens, so these people dare not drink the water overnight. However, scientific research shows that if the water is pure water after a night, it will not have much chemical reaction and will not produce harmful substances. Therefore, water can be drunk overnight, not only overnight, but even after a day, as long as it is protected and there is no dust, it can be drunk as long as it falls inside. Scientific research has found that even after 2-3 days, the harmful substances produced in boiling water are very limited.