Xiao Xu
Water plays an important role in our lives, it is the source of life, and it is one of the important material resources on which human beings rely for survival and development. We can't live without water for a moment, and the topic we are discussing today is also related to water.
Xiao Xu, just say it directly, what is wrong with the water again?
Professor Cheng
Xiao Xu
Many people will dry some boiled water at home, but there has always been a saying that "overnight water cannot be drunk", because overnight water can cause diarrhea, and there is even a saying that "boiled water will produce carcinogens if left for 3 days", which makes many people feel scared. Professor Cheng, please tell us!
Carcinogens do not arise in a vacuum. It is important to know that nitrite, the most feared carcinogen, is unlikely to be present in plain water with only minerals and trace elements. There is no scientific basis for the statement that "carcinogens will be produced when boiled water is left for 3 days".
Professor Cheng
Mr. Cao
But I found that the taste of boiled water overnight is not the same as that of boiling water directly, is this because the overnight water has gone bad? If it doesn't deteriorate, why does overnight water smell bad?
This is mainly because when boiled water is exposed to the air for a long time, a small amount of carbon dioxide in the air will dissolve into it, and after some chemical reactions, the taste will change. Although there is no fatal harm, boiled water that has been left for a few days is easy to be contaminated with bacteria, so it is better not to drink it.
Professor Cheng
Xiao Xu
Professor Cheng, there is another question that has always bothered me, have you ever heard of "a thousand boiling water causes cancer"? Is it possible to drink water that has been boiled repeatedly?
As long as the water quality can be guaranteed or the tools used to boil the water meet the safety and quality standards, the water will theoretically not produce carcinogens even if it is boiled many times. Whether at home or abroad, there is no scientific basis to suggest that "a thousand boiling water causes cancer". However, from a health point of view, it is recommended that everyone drink freshly boiled water.
Professor Cheng
Xiao Xu
There is also the fact that we often use kettles for boiling water, and after using them for a long time, white scale will appear in them, what is this?
The water contains minerals, and the inner wall of the kettle will form a thick white scale, which is a manifestation of the presence of minerals, and in this sense, boiled water is also a kind of "mineral water".
Professor Cheng
Mr. Cao
The presence of these minerals in water has any effect on the human body?
In fact, the mineral content in the water is very small, and it will not have a big impact on the replenishment of minerals needed by the human body, and the minerals required by the human body are generally obtained from other foods.
Professor Cheng
Xiao Xu
Similar to "you can't drink water overnight", there is also a saying that "the shelf life of boiled water is only 16 hours", is there any scientific basis for this statement?
Water kills a lot of deadly microorganisms during the boiling process, but after the temperature of boiled water drops to room temperature, various microorganisms continue to enter and multiply in the water. The longer the exposure to the air, the greater the number of microorganisms and the consequent deterioration of water quality. It may not be as accurate as 16 hours, but the quality of boiled water that has just been boiled and cooled, boiled water that has been left overnight or left for a long time is not as good as before.
Professor Cheng
Mr. Cao
It seems that for people with fragile stomachs, such as children, it is better to drink fresh plain water.
Xiao Xu
Professor Cheng, generally the water dispenser we use at home or at work, a bucket of water often has to be left for about a week, it stands to reason that it has already exceeded the "shelf life" of water, so should we not drink it anymore?
At present, the regular bottled water has taken corresponding sterilization and sealing measures, and if the water dispenser can be kept clean, it can be drunk with confidence.
Professor Cheng
Xiao Xu
Then I'm relieved. Professor Cheng, I also saw a saying on the Internet, "You also need to turn on the range hood when boiling water", is there any scientific basis for this statement?
For boiling water, cooking, and stir-frying, it is best to turn on the range hood or exhaust fan to exhaust the water vapor as much as possible. If the water vapor in the kitchen is not discharged in time and clings to the corners, a large amount of mold will grow. Mold can easily cause allergies, if you have allergies at home, you should remove it in time and prevent mold from occurring.
Professor Cheng
Xiao Xu
There are also some people who turn off the fire as soon as the water is boiled when they boil it, is this practice right? How long should water boil before turning off the heat?
Boiling water is the best sterilization method, but the excrement of microorganisms in the water, especially the endotoxin released by pathogenic bacteria after being killed, cannot be killed at 100°C, so the water should be boiled for 2~3 minutes before turning off the fire.
Professor Cheng
Xiao Xu
Do you have to lift the lid when the water is about to boil?
When boiling water, when the temperature of the water is close to 100 °C, the lid of the kettle should be opened to let out some of the residual volatile organic compounds in the water, and then turn off the fire after boiling for 2~3 minutes.
Professor Cheng
Xiao Xu
I know if you have noticed that as long as we have any discomfort in our body, we always drink plain water first, whether it is abdominal pain or headache, there is nothing that cannot be solved by vain.
Mr. Cao
That's why water is called the source of life! But do people really drink water? How to drink water healthily?
A study found that as long as you insist on drinking a glass of 500ml of water half an hour before each meal, you can lose 2~4 kg of weight after 3 months.
Professor Cheng
Xiao Xu
In fact, this is somewhat similar to what we often say "drink soup before meals". First, eating can be reduced by increasing satiety; Secondly, food cravings will also change. Because there is enough water, the body will prefer protein and absorb less fattening carbohydrates.
Yes, if you feel stomach acid, you can relieve it by drinking soda. If you feel miserable or irritable, you can also drink plenty of water, which may improve your mood.
Professor Cheng
Xiao Xu
Thank you very much Professor Cheng for your popular science!
Content Sources:
People's Medical Publishing House published "Safety on the Tip of the Tongue (Volume 4)"
Editor-in-Chief of the book:
Cheng Jingmin, an expert of the National Health Science Popularization Expert Database and a professor of Shanxi Medical University
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