Zhejiang Online December 12 news? ( Qianjiang Evening News chief reporter Li Yangyang intern Lu Yuanyuan Zhang Lingling / text Liang Ziming / chart) water is the source of life, and the most healthy than boiled water. However, recently, a rumor about the network of white water circulated online: overnight water can not drink? Cold boiled water for a long time is comparable to chronic poison? Repeated boiling water will cause cancer?

Many of these statements do not sound familiar, yes, go online search, these statements have been considered "old rumors", so they are true, or false, a cup of water because of the burning method or drink method is not right, will not be as horrible as the Internet said?

The Qianjiang Evening News reporter asked two experts: Huazhong University of Science and Technology Tongji Medical College, Professor Wu Zhigang, Hangzhou Xiaoshan District Health Association of nutritionist Hu Wengang.

While experts have different opinions on some details, there is a **** knowledge of the Internet rumor itself: the rumor claim is too radical, unreliable.

Should boiling water be boiled for another 3 minutes?

Experts: boil for a while longer can have, remember to open the lid:

Originally published on the Internet:

Water should continue to boil for 3 minutes after boiling, because only in this way can remove the chloride in the tap water, and continue to heat it so that these chlorides can be drifted away along with the water vapor.

Expert Answer:

For the water to boil a little while longer, the experts are unanimous in saying that there is nothing wrong with more burning, but the 3-minute limit lacks scientific basis.

Huazhong University of Science and Technology Tongji Medical College, Professor Wu Zhigang School of Public **** Health, that tap water should indeed continue to boil after boiling, but do not need to necessarily have to wait 3 minutes. "Tap water will be chlorinated to disinfect it when it is processed, and boiling it for a little while is conducive to the volatilization of residual chlorine. Time depends on the situation, 1 or 2 minutes is also enough." Wu Zhigang special reminder, after boiling continue to boil, be sure to open the lid to facilitate the volatilization of residual chlorine.

From the nutritional point of view of water, Hu Wengang, a nutritionist with the Health Care Association of Xiaoshan District, Hangzhou, believes that not only should it be boiled for a while longer, but it should also be put out of the fire for a little while. "Tap water itself contains some organic matter, boiling process will form calcium substances, but calcium itself will not float away with the water vapor, but has been in the water, the longer the burning time, the amount of water as evaporation becomes less, the corresponding increase in the content of calcium, that is to say, the concentration of calcium in the water will become higher. Therefore, after boiling and put a while, is conducive to the precipitation of calcium in the water."

According to Hu Wengang, this will also make the water taste a little better, so why not try it right away?

Thousand rolls of water, repeated boiling will cause cancer?

Experts: poisoning through a thousand rolls of water is very uncommon

Original web article:

The thousand rolls of water is the water that boils overnight or for a very long time on the stove, as well as the water that is boiled over and over again in the electric water heater. Office buildings in the white-collar workers usually drink most of the water is boiling water room or boiler burned out of this water due to repeated boiling, will lead to an increase in nitrites and other harmful substances, toxic nitrites will also cause hypoxia, severe coma and convulsions, and even death.

Expert Answer:

Water repeatedly boiled will cause cancer? Every day drinking boiler water office workers is not very worried, good thing experts do not agree with this sensationalist claims.

All in all, the so-called poisoning are around the "nitrite", which is a class of inorganic compounds, mainly sodium nitrite. Sodium nitrite taste slightly salty, soluble in water, appearance and taste similar to table salt, widely used in industry, construction, meat products, also allows it to be used as a coloring agent limited use of nitrites caused by food poisoning due to the higher chance, so the state of the use of nitrites have strict control.

How can there be such substances in tap water? The reason is that people drink water from natural surface water or groundwater. Because nitrates and nitrites are soluble in water, nitrates and nitrites in surface water may also slowly infiltrate into groundwater; in addition, nitrates contained in water sources may be contaminated by microorganisms and transformed into nitrites.

While nitrite is carcinogenic, it is not really easy to cause cancer through nitrite in water. General human one-time safe intake of nitrite for each kilogram of body weight 0.2 mg, living drinking water health standards, the provisions of nitrite content does not exceed 10 mg / liter, if you do not drink more than 10 liters of water at one time, then it is safe.

As for the thousand rolls of water, resulting in "nitrite" content of the same statement is only a speculation. "Thousand rolls of water harmful to human health rumors are no scientific basis, to be poisoned by a thousand rolls of water is very difficult." Wu Zhigang said.

This time there is data to support the conclusion of the experiment from a university: with the increase in the number of times of boiling, the nitrite content of the water does not have a significant upward trend. And all water samples of nitrite content, are lower than China's "drinking water health standards" (GB5749-2006) in the nitrite content limit of 10 mg / liter. Specific data can be seen in the picture on this page, the nitrite content of thousand rolls of water is even lower than mineral water.

A cup of life of up to 16 hours?

Experts: the day of boiling water is best drunk on the same day

Internet original:

A cup of water has a shelf life of only 16 hours, the total number of bacteria in the overnight white water is higher than that in the tap water.

According to experimental data, boiled white water, placed in the air for 16 hours, the total number of E. coli bacteria will be a serious exceeding of the phenomenon, therefore, the white water in the boiling 3 minutes after turning off the fire the moment you start, there is a 16-hour shelf life.

Expert answer:

Hu Wengang agreed that water has a shelf life, but he felt that "16 hours" is not based on science.

He said the water has a shelf life, in fact, quite understandable, drinking raw water is easy to diarrhea, because the water will have a variety of micro-organisms, bacteria, and after high-temperature cooking, these micro-organisms, bacteria can not survive, are killed.

However, in the process of boiling water cooled down, the temperature is just perfect for microorganisms, bacteria reproduction, the longer the time to reproduce the more, just like a pot of water outside, time will be spoiled.

How long will go bad, will not be suitable for drinking, in fact, there is no fixed time, because it is also affected by the objective environment. For example, the temperature, in the summer, the temperature is more than 30 degrees Celsius, the air humidity is high, the bacteria multiply faster, it is very easy to be contaminated and cause diarrhea.

So, it's best not to drink overnight water in summer, and in winter it's best to put it in a cup with a lid and drink it the next morning with boiled water to warm water.

Wu Zhigang suggests, "Cold white water should not be left for too long, and it is best to drink the boiled water on the same day."

While Hu Wengang that the online rumors of boiling water in the air shelf life of only 16 hours belongs to the netizen's personal views, there is no relevant experiments and data to prove that the boiling water should not be placed for too long, even if there is no shelf life, after several days of boiled water is best not to drink again.

Finally, a little knowledge about water -

The water at home is white?

The water that comes out of your home starts out white and after a few minutes turns clear again.

In fact, this is a normal phenomenon. This phenomenon in the water supply inside the small knowledge called water vapor mixing phenomenon, is by the water supply pump impeller in high-speed rotation of water, part of the air decomposition to the water, and then released from the tap, the pressure becomes smaller, the dissolved air re-decomposition of water from the water will produce fine bubbles, then it looks like the water will show the phenomenon of whiteness, and wait for the gradual disappearance of the bubbles, the water will return to the color of the transparent, the case! This will not affect the normal water quality.