Water is an essential and indispensable substance for human survival. A person can go a day without food, but not a day without water. However, not all water is suitable for drinking. The following five types of water can form nitrites and other toxic and harmful substances to a certain extent, posing certain hazards to the human body and thus requiring people's attention. I. Stagnant Water
Commonly known as "dead water," it is water that has been stored for a long time without movement. Drinking this water often can significantly slow down the metabolism of cells in minors, affecting physical growth and development; in middle-aged and elderly people, it can accelerate aging. In many places, the incidence of esophageal and stomach cancer is increasing daily. According to medical research, this may be related to long-term consumption of stagnant water. Relevant data indicates that the toxic substances in stagnant water also increase with the length of storage time. II. Reboiled Water
Reboiled water is water that has been boiling on a stove all night or for a long time, as well as water repeatedly boiled in an electric water heater. Due to prolonged boiling, this water has high levels of non-volatile substances, such as heavy metal components like calcium and magnesium, and a high nitrite content. Drinking this water for a long time can interfere with gastrointestinal function, causing temporary diarrhea and bloating. Toxic nitrites can also cause hypoxia in the body; in severe cases, it can lead to coma and convulsions, and even death. III. Steamer Water
Steamer water is the leftover water from cooking steamed buns and other foods. Especially when repeatedly used, the nitrite concentration in steamer water is very high. Drinking this water often, or using it to cook congee, can cause nitrite poisoning. The scale that often enters the human body with the water can also cause diseases of the digestive, nervous, urinary, and hematopoietic systems, and even cause premature aging. IV. Unboiled Water
The tap water people drink is disinfected and sterilized by chlorination. In chlorinated water, 13 harmful substances can be separated, among which halogenated hydrocarbons and chloroform have carcinogenic and teratogenic effects. When the water temperature reaches 90°C, the content of halogenated hydrocarbons increases from the original 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 likelihood of developing bladder and rectal cancer by 21% to 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 3 more minutes, it is safe to drink. V. Reboiled Water
Some people have the habit of reboiling the remaining warm water in a thermos for drinking, with the intention of saving water, coal (gas), and time. However, this kind of "saving" is not advisable. Because the water is boiled again, the water evaporates again, and nitrites increase. Drinking this water often can cause nitrites to accumulate in the body and lead to poisoning.