Water is essential for human activity, and people consume a large amount of it. For various reasons, some water contains harmful substances that can endanger human health. Note! The following types of water must never be consumed!
1. Stagnant Water
When boiled water is left standing for a long time, the nitrogen-containing organic matter in it will continuously decompose into nitrites. Especially with boiled water that has been stored for too long, bacterial contamination is inevitable, which accelerates the decomposition of nitrogen-containing organic matter and leads to the formation of even more nitrites. After drinking such water, nitrites combine with hemoglobin, affecting the blood's ability to transport oxygen.
Therefore, boiled water that has been in a thermos for several days, the remaining water from multiple boilings, or water that has been boiling on a stove for a long time has already undergone chemical changes and should not be consumed. You should drink water that has been boiled once and is not older than 24 hours. In addition, bottled and桶装 (barreled) purified water and mineral water should not be stored for too long. Large bottles or barrels of purified water and mineral water should not be consumed after 3 days.
2. Unboiled Water
The tap water people drink is sterilized by chlorination. Chlorinated water can also separate into 13 harmful substances, 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 53 micrograms per kilogram to 177 micrograms, which is twice the national drinking water hygiene standard.
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 decrease with the evaporation of the water. If boiled for another 3 minutes, it will be safer to drink.
3. Water from the Tap First Thing in the Morning
Some people have the habit of turning on the tap in the morning and filling a glass of tap water to drink, which is incorrect.
The tap water in a faucet and pipes that have been unused overnight is stagnant. This water reacts with the metal pipe walls and the faucet's metal chamber, causing contamination. In addition, residual microorganisms in the tap water can multiply and produce an acute respiratory infectious bacterium—Legionella.
4. Aging Water
Commonly known as "dead water," it is water that has been stored for a long time without moving. Drinking this water often will, for minors, significantly slow down cell metabolism and affect physical development; for middle-aged and elderly people, it will accelerate aging.
Furthermore, studies show that the increasing incidence of esophageal and stomach cancer in many places may be related to long-term consumption of aging water. Relevant data indicates that the toxic substances in aging water increase with the length of storage time.
5. Freshly Boiled Tap Water
Many people enjoy drinking boiled water, but did you know? Water should not be drunk as soon as it is boiled. Because our tap water is disinfected with chlorine, the chlorine in it combines with residual organic matter to produce various carcinogenic compounds such as halogenated hydrocarbons and chloroform.
The correct method: first, draw the tap water and let it sit for a while before boiling; when the water is about to boil, open the kettle lid; finally, after the water has boiled, let it continue to boil for 3 minutes before turning off the heat. This will reduce the chlorine content in the water to a safe drinking standard, making it truly "boiled water."
6. Re-boiled Water
Nowadays, more and more households use electric kettles. Many people cannot finish a pot of boiled water at once and re-boil it later; or they re-boil the remaining warm water from a thermos to drink, with the intention of saving water, coal (gas), and time. These practices are not advisable.
Boiling water repeatedly causes more water to evaporate, and the nitrite content will rise. Drinking this kind of water often can cause nitrites to accumulate in the body and lead to poisoning.
Friendly Reminder: Under limited real-world conditions, if you have consumed any of the above 6 types of water, you should pay close attention to your physical condition. If you feel unwell or have any other adverse reactions, you should stop drinking immediately and seek medical help.