The following five types of water, to some extent, can form nitrites and other toxic and harmful substances, which can pose certain hazards to the human body.
Aging water: Commonly known as 'stagnant water,' it is water that has been stored for a long time without moving. Drinking this water often can significantly slow down cell metabolism in minors, affecting physical development; in middle-aged and elderly people, it can accelerate aging. The increasing incidence of esophageal and stomach cancer in many places may be related to long-term consumption of aging water. The toxic substances in aging water also increase with the storage time of the water.
Boiled-over water: This is water that has been boiling on a stove all night or for a very long time, as well as water in an electric water heater that has been repeatedly boiled. Due to prolonged boiling, this water contains high levels of non-volatile substances, such as heavy metals like calcium and magnesium, and a high nitrite content. Drinking this water for a long time can interfere with human gastrointestinal function, causing temporary diarrhea and bloating; toxic nitrites can also cause hypoxia in the body, and in severe cases, lead to coma, convulsions, and even death.
Steamer water: This is the leftover water from a steamer after steaming items like steamed buns. The nitrite concentration in steamer water that has been used repeatedly is very high. Drinking this water often, or using it to cook porridge, can cause nitrite poisoning. The limescale often enters the human body with the water, which can also cause digestive, nervous, urinary, and hematological system disorders, and even premature aging.
Unboiled water: The tap water people drink is disinfected and sterilized by chlorination. Chlorinated water can separate 13 harmful substances, of which halogenated hydrocarbons and chloroform are carcinogenic and teratogenic. When the water temperature reaches 90°C, the content of halogenated hydrocarbons increases from 53 micrograms per kilogram to 177 micrograms, exceeding the national drinking water hygiene standard by 2 times. Experts point out that drinking unboiled water increases the risk of bladder cancer and rectal cancer by 21%-38%. When the water temperature reaches 100°C, these two harmful substances will greatly reduce with the evaporation of steam. If boiling is continued for another 3 minutes, it is safe to drink.
Re-boiled water: Some people are in the habit of re-boiling the remaining warm water in a thermos for the purpose of saving water, coal (gas), and time. However, this kind of 'savings' is not advisable. Because the water is boiled again, the water evaporates again, and nitrites will increase. Drinking this water often can lead to an accumulation of nitrites in the body.