Why does hot water freeze faster than cold water?

At what temperature does water freeze? It would seem - the simplest question that even a child can answer: the freezing point of water at normal atmospheric pressure of 760 mmHg is zero degrees Celsius.

However, water (despite its extremely wide distribution on our planet) is the most mysterious and not fully understood substance, so the answer to this question requires a detailed and reasoned discussion.

In Russia and Europe, the temperature is measured on the Celsius scale, the highest value of which is 100 degrees.
The American scientist Fahrenheit developed his own scale with 180 divisions.
There is another unit of temperature measurement - kelvin, named after the English physicist Thomson, who received the title of Lord Kelvin.

States and types of water

Water on planet Earth can take three main states of aggregation: liquid, solid and gaseous, which can transform into different forms that simultaneously coexist with each other (icebergs in sea water, water vapor and ice crystals in clouds in the sky, glaciers and free-flowing rivers ).

Depending on the characteristics of the origin, purpose and composition, water can be:

fresh;
mineral;
nautical;
drinking (here we include tap water);
rain;
thawed;
brackish;
structured;
distilled;
deionized.

The presence of hydrogen isotopes makes water:

light;
heavy (deuterium);
superheavy (tritium).

We all know that water can be soft and hard: this indicator is determined by the content of magnesium and calcium cations.

Each of the types and aggregate states of water we have listed has its own freezing and melting point.

Freezing point of water

Why does water freeze? Ordinary water always contains some amount of suspended particles of mineral or organic origin. It can be the smallest particles of clay, sand or house dust.

When the ambient temperature drops to certain values, these particles take on the role of centers around which ice crystals begin to form.

Air bubbles, as well as cracks and damage on the walls of the vessel in which water is located, can also become crystallization nuclei. The rate of water crystallization is largely determined by the number of these centers: the more of them, the faster the liquid freezes.

Under normal conditions (at normal atmospheric pressure), the temperature of the phase transition of water from a liquid to a solid state is 0 degrees Celsius. It is at this temperature that water freezes on the street.

Why does hot water freeze faster than cold water?

Hot water freezes faster than cold water - this phenomenon was noticed by Erasto Mpemba, a schoolboy from Tanganyika. His experiments with mass for making ice cream showed that the rate of freezing of the heated mass is much higher than the cold one.

One of the reasons for this interesting phenomenon, called the "Mpemba paradox", is the higher heat transfer of a hot liquid, as well as the presence of a larger number of crystallization nuclei in it compared to cold water.

Are the freezing point of water and altitude related?

With a change in pressure, often associated with being at different heights, the freezing point of water begins to radically differ from the standard, characteristic of normal conditions.
Crystallization of water at a height occurs at the following temperature values:

paradoxically, at an altitude of 1000 m, water freezes at 2 degrees Celsius;
at an altitude of 2000 meters, this happens already at 4 degrees Celsius.

The highest freezing temperature of water in the mountains is observed at an altitude of over 5,000 thousand meters (for example, in the Fann Mountains or the Pamirs).

How does pressure affect the process of water crystallization?

Let's try to link the dynamics of changes in the freezing point of water with changes in pressure.

At a pressure of 2 atm, water will freeze at a temperature of -2 degrees.
At a pressure of 3 atm, the temperature of -4 degrees Celsius will begin to freeze water.

With increased pressure, the temperature of the beginning of the water crystallization process decreases, and the boiling point increases. At low pressure, a diametrically opposite picture is obtained.

That is why in conditions of high mountains and a rarefied atmosphere it is very difficult to cook even eggs, since the water in the pot boils already at 80 degrees. It is clear that at this temperature it is simply impossible to cook food.

At high pressure, the process of ice melting under the blades of the skates occurs even at very low temperatures, but it is thanks to it that the skates glide on the ice surface.

The freezing of skids of heavily loaded sleds in the stories of Jack London is explained in a similar way. Heavy sleds that put pressure on the snow cause it to melt. The resulting water facilitates their sliding. But as soon as the sleds stop and linger for a long time in one place, the displaced water, freezing, freezes the skids to the road.

Crystallization temperature of aqueous solutions

Being an excellent solvent, water easily reacts with various organic and inorganic substances, forming a mass of sometimes unexpected chemical compounds. Of course, each of them will freeze at different temperatures. Let's put this in a visual list.

The freezing point of a mixture of alcohol and water depends on the percentage of both components in it. The more water added to the solution, the closer to zero its freezing point. If there is more alcohol in the solution, the crystallization process will begin at values close to -114 degrees.
It is important to know that water-alcohol solutions do not have a fixed freezing point. Usually they talk about the temperature of the beginning of the crystallization process and the temperature of the final transition to the solid state.
Between the beginning of the formation of the first crystals and the complete solidification of the alcohol solution lies a temperature interval of 7 degrees. So, the freezing point of water with alcohol of 40% concentration at the initial stage is -22.5 degrees, and the final transition of the solution to the solid phase will occur at -29.5 degrees.

The freezing point of water with salt is closely related to the degree of its salinity: the more salt in the solution, the lower the position of the mercury column it will freeze.

To measure the salinity of water, a special unit is used - "ppm". So, we have found that the freezing point of water decreases with increasing salt concentration. Let's explain this with an example:

The salinity level of ocean water is 35 ppm, while the average value of its freezing is 1.9 degrees. The degree of salinity of the Black Sea waters is 18-20 ppm, so they freeze at a higher temperature in the range from -0.9 to -1.1 degrees Celsius.

The freezing point of water with sugar (for a solution whose molality is 0.8) is -1.6 degrees.
The freezing point of water with impurities largely depends on their amount and the nature of the impurities that make up the aqueous solution.
The freezing point of water with glycerin depends on the concentration of the solution. A solution containing 80 ml of glycerin will freeze at -20 degrees, when the glycerol content is reduced to 60 ml, the crystallization process will begin at -34 degrees, and the beginning of freezing of a 20% solution will be minus five degrees. As you can see, there is no linear relationship in this case. To freeze a 10% solution of glycerin, a temperature of -2 degrees will suffice.
The freezing point of water with soda (meaning caustic alkali or caustic soda) presents an even more mysterious picture: a 44% caustic solution freezes at +7 degrees Celsius, and 80% at + 130.

Freezing of fresh water

The process of ice formation in freshwater reservoirs occurs in a slightly different temperature regime.

The freezing point of water in a lake, just like the freezing point of water in a river, is zero degrees Celsius. The freezing of the cleanest rivers and streams does not start from the surface, but from the bottom, on which there are crystallization nuclei in the form of bottom silt particles. At first, snags and aquatic plants are covered with a crust of ice. As soon as the bottom ice rises to the surface, the river instantly freezes through.
Frozen water on Lake Baikal can sometimes cool down to negative temperatures. This happens only in shallow water; the water temperature in this case can be thousandths, and sometimes hundredths of one degree below zero.
The temperature of the Baikal water under the very crust of the ice cover, as a rule, does not exceed +0.2 degrees. In the lower layers, it gradually rises to +3.2 at the bottom of the deepest basin.

Freezing point of distilled water

Does distilled water freeze? Recall that for water to freeze, it is necessary to have some crystallization centers in it, which can be air bubbles, suspended particles, as well as damage to the walls of the container in which it is located.

Distilled water, completely devoid of any impurities, does not have crystallization nuclei, and therefore its freezing begins at very low temperatures. The initial freezing point of distilled water is -42 degrees. Scientists managed to achieve supercooling of distilled water to -70 degrees.

Water that has been exposed to very low temperatures but has not crystallized is called "supercooled". You can place a bottle of distilled water in the freezer, get it supercooled, and then demonstrate a very effective trick - see the video:

By gently tapping on a bottle taken from the refrigerator, or by throwing a small piece of ice into it, you can show how it instantly turns into ice, which looks like elongated crystals.

Distilled water: does this purified substance freeze or not under pressure? Such a process is possible only in specially created laboratory conditions.

Freezing point of salt water

Which water freezes faster, hot or cold, is influenced by many factors, but the question itself seems a little strange. It is understood, and it is known from physics, that hot water still needs time to cool down to the temperature of comparable cold water in order to turn into ice. this stage can be skipped, and, accordingly, she wins in time.

But the answer to the question of which water freezes faster - cold or hot - on the street in frost, any inhabitant of the northern latitudes knows. In fact, scientifically, it turns out that in any case, cold water simply has to freeze faster.

So did the teacher of physics, who was approached by the schoolboy Erasto Mpemba in 1963 with a request to explain why the cold mixture of future ice cream freezes longer than a similar, but hot one.

"This is not world physics, but some kind of Mpemba physics"

At that time, the teacher only laughed at this, but Deniss Osborne, a professor of physics, who at one time went to the same school where Erasto studied, experimentally confirmed the existence of such an effect, although there was no explanation for this then. In 1969 a popular scientific journal published a joint article by the two men who described this peculiar effect.

Since then, by the way, the question of which water freezes faster - hot or cold, has its own name - the effect, or paradox, Mpemba.

The question has been around for a long time

Naturally, such a phenomenon has taken place before, and it was mentioned in the works of other scientists. Not only the schoolboy was interested in this question, but Rene Descartes and even Aristotle thought about it at one time.

Here are just approaches to solving this paradox began to look only at the end of the twentieth century.

Conditions for a paradox to occur

As with ice cream, it's not just ordinary water that freezes during the experiment. Certain conditions must be present in order to start arguing which water freezes faster - cold or hot. What influences this process?

Now, in the 21st century, several options have been put forward that can explain this paradox. Which water freezes faster, hot or cold, may depend on the fact that it has a higher evaporation rate than cold water. Thus, its volume decreases, and with a decrease in volume, the freezing time becomes shorter than if we take a similar initial volume of cold water.

Freezer has long been defrosted

Which water freezes faster, and why it does so, can be affected by the snow lining that may be present in the freezer of the refrigerator used for the experiment. If you take two containers that are identical in volume, but one of them will have hot water and the other cold water, the container with hot water will melt the snow under it, thereby improving the contact of the thermal level with the refrigerator wall. A cold water container can't do that. If there is no such lining with snow in the refrigerator, cold water should freeze faster.

Top - bottom

Also, the phenomenon of which water freezes faster - hot or cold, is explained as follows. Following certain laws, cold water starts to freeze from the upper layers, when hot water does it the other way around - it starts to freeze from the bottom up. It turns out that cold water, having a cold layer on top with ice already formed in some places, thus worsens the processes of convection and thermal radiation, thereby explaining which water freezes faster - cold or hot. A photo from amateur experiments is attached, and here it is clearly visible.

The heat goes out, tending upwards, and there it meets a very cool layer. There is no free path for heat radiation, so the cooling process becomes difficult. Hot water has absolutely no such barriers in its path. Which freezes faster - cold or hot, on which the probable outcome depends, you can expand the answer by saying that any water has certain substances dissolved in it.

Impurities in the composition of water as a factor influencing the outcome

If you do not cheat and use water with the same composition, where the concentrations of certain substances are identical, then cold water should freeze faster. But if a situation occurs when dissolved chemical elements are present only in hot water, while cold water does not possess them, then hot water has the opportunity to freeze earlier. This is explained by the fact that the dissolved substances in water create centers of crystallization, and with a small number of these centers, the transformation of water into a solid state is difficult. Even supercooling of water is possible, in the sense that at sub-zero temperatures it will be in a liquid state.

But all these versions, apparently, did not suit the scientists to the end, and they continued to work on this issue. In 2013, a team of researchers in Singapore said they had solved the age-old mystery.

A group of Chinese scientists claim that the secret of this effect lies in the amount of energy that is stored between water molecules in its bonds, called hydrogen bonds.

The answer from Chinese scientists

Further information will follow, for the understanding of which it is necessary to have some knowledge in chemistry in order to figure out which water freezes faster - hot or cold. As you know, it consists of two H (hydrogen) atoms and one O (oxygen) atom held together by covalent bonds.

But hydrogen atoms of one molecule are also attracted to neighboring molecules, to their oxygen component. These bonds are called hydrogen bonds.

At the same time, it is worth remembering that at the same time, water molecules act repulsively on each other. Scientists noted that when water is heated, the distance between its molecules increases, and this is facilitated by repulsive forces. It turns out that occupying one distance between molecules in a cold state, one can say that they stretch, and they have a greater supply of energy. It is this energy reserve that is released when water molecules begin to approach each other, that is, cooling occurs. It turns out that a larger supply of energy in hot water, and its greater release when cooled to sub-zero temperatures, occurs faster than in cold water, which has a smaller supply of such energy. So which water freezes faster - cold or hot? On the street and in the laboratory, the Mpemba paradox should occur, and hot water should turn into ice faster.

But the question is still open

There is only theoretical confirmation of this clue - all this is written in beautiful formulas and seems plausible. But when the experimental data, which water freezes faster - hot or cold, will be put in a practical sense, and their results will be presented, then it will be possible to consider the question of the Mpemba paradox closed.

Mpemba effect(Mpemba paradox) - a paradox that states that hot water under certain conditions freezes faster than cold water, although it must pass the temperature of cold water in the process of freezing. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a hotter body needs more time to cool down to a certain temperature than a cooler body to cool down to the same temperature.

This phenomenon was noticed at the time by Aristotle, Francis Bacon and Rene Descartes, but only in 1963, the Tanzanian schoolboy Erasto Mpemba found that a hot ice cream mixture freezes faster than a cold one.

Erasto Mpemba was a student at Magambin High School in Tanzania doing practical cooking work. He had to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and procrastinated on the first part of the assignment. Fearing that he would not be in time by the end of the lesson, he put the still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to a given technology.

After that, Mpemba experimented not only with milk, but also with ordinary water. In any case, already being a student at Mkwawa High School, he asked Professor Dennis Osborne from the University College in Dar es Salaam (invited by the director of the school to give a lecture on physics to students) about water: "If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35 ° C, and in the other - 100 ° C, and put them in the freezer, then in the second the water will freeze faster. Why? Osborne became interested in this issue and soon in 1969, together with Mpemba, they published the results of their experiments in the journal "Physics Education". Since then, the effect they discovered is called Mpemba effect.

Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection, or the effect of liquefied gases on water at different temperatures.

The paradox of the Mpemba effect is that the time during which the body cools down to the ambient temperature must be proportional to the temperature difference between this body and the environment. This law was established by Newton and since then has been confirmed many times in practice. In the same effect, water at 100°C cools down to 0°C faster than the same amount of water at 35°C.

However, this does not yet imply a paradox, since the Mpemba effect can also be explained within known physics. Here are some explanations for the Mpemba effect:

Evaporation

Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water with the same temperature freezes faster. Water heated to 100 C loses 16% of its mass when cooled to 0 C.

The evaporation effect is a double effect. First, the mass of water required for cooling is reduced. And secondly, the temperature decreases due to the fact that the heat of evaporation of the transition from the water phase to the vapor phase decreases.

temperature difference

Due to the fact that the temperature difference between hot water and cold air is greater - hence the heat exchange in this case is more intense and hot water cools faster.

hypothermia

When water is cooled below 0 C, it does not always freeze. Under certain conditions, it can undergo supercooling while continuing to remain liquid at temperatures below the freezing point. In some cases, water can remain liquid even at -20 C.

The reason for this effect is that in order for the first ice crystals to begin to form, centers of crystal formation are needed. If they are not in liquid water, then supercooling will continue until the temperature drops enough that crystals begin to form spontaneously. When they start to form in the supercooled liquid, they will start to grow faster, forming an ice slush that will freeze to form ice.

Hot water is most susceptible to hypothermia because heating it eliminates dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals.

Why does hypothermia cause hot water to freeze faster? In the case of cold water, which is not supercooled, the following occurs. In this case, a thin layer of ice will form on the surface of the vessel. This layer of ice will act as an insulator between the water and cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be less. In the case of hot water undergoing subcooling, the subcooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top.

When the supercooling process ends and the water freezes, much more heat is lost and therefore more ice is formed.

Many researchers of this effect consider hypothermia to be the main factor in the case of the Mpemba effect.

Convection

Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence the loss of heat, while hot water begins to freeze from below.

This effect is explained by an anomaly in the density of water. Water has a maximum density at 4 C. If you cool water to 4 C and put it at a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at 4°C, it will stay on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water for a short time, but this layer of ice will serve as an insulator protecting the lower layers of water, which will remain at a temperature of 4 C. Therefore, further cooling will be slower.

In the case of hot water, the situation is completely different. The surface layer of water will cool more quickly due to evaporation and a greater temperature difference. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, lifting the warm water layer to the surface. This circulation of water ensures a rapid drop in temperature.

But why does this process not reach the equilibrium point? To explain the Mpemba effect from this point of view of convection, it would be necessary to assume that the cold and hot layers of water are separated and the convection process itself continues after the average water temperature drops below 4 C.

However, there is no experimental evidence to support this hypothesis that cold and hot water layers are separated by convection.

gases dissolved in water

Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to lower the freezing point of water. When the water is heated, these gases are released from the water because their solubility in water at high temperature is lower. Therefore, when hot water is cooled, there are always fewer dissolved gases in it than in unheated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main one in explaining the Mpemba effect, although there are no experimental data confirming this fact.

Thermal conductivity

This mechanism can play a significant role when water is placed in a refrigerator freezer in small containers. Under these conditions, it has been observed that the container with hot water melts the ice of the freezer under itself, thereby improving thermal contact with the wall of the freezer and thermal conductivity. As a result, heat is removed from the hot water container faster than from the cold one. In turn, the container with cold water does not melt snow under it.

All these (as well as other) conditions have been studied in many experiments, but an unequivocal answer to the question - which of them provide a 100% reproduction of the Mpemba effect - has not been obtained.

So, for example, in 1995, the German physicist David Auerbach studied the influence of water supercooling on this effect. He discovered that hot water, reaching a supercooled state, freezes at a higher temperature than cold water, and therefore faster than the latter. But cold water reaches the supercooled state faster than hot water, thereby compensating for the previous lag.

In addition, Auerbach's results contradicted earlier data that hot water is able to achieve more supercooling due to fewer crystallization centers. When water is heated, gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate.

So far, only one thing can be asserted - the reproduction of this effect essentially depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.

O. V. Mosin

Literarysources:

"Hot water freezes faster than cold water. Why does it do so?", Jearl Walker in The Amateur Scientist, Scientific American, Vol. 237, no. 3, pp. 246-257; September, 1977.

"The Freezing of Hot and Cold Water", G.S. Kell in American Journal of Physics, Vol. 37, no. 5, pp. 564-565; May 1969.

"Supercooling and the Mpemba effect", David Auerbach, in American Journal of Physics, Vol. 63, no. 10, pp. 882-885; Oct, 1995.

"The Mpemba effect: The freezing times of hot and cold water", Charles A. Knight, in American Journal of Physics, Vol. 64, no. 5, p 524; May, 1996.

Water is one of the most amazing liquids in the world, which has unusual properties. For example, ice - a solid state of liquid, has a specific gravity lower than water itself, which made the emergence and development of life on Earth in many ways possible. In addition, in the near-scientific, and indeed the scientific world, there are discussions about which water freezes faster - hot or cold. Whoever proves faster freezing of a hot liquid under certain conditions and scientifically substantiates his decision will receive an award of £1,000 from the British Royal Society of Chemists.

Background

The fact that, under a number of conditions, hot water is ahead of cold water in terms of freezing rate, was noticed back in the Middle Ages. Francis Bacon and René Descartes have put a lot of effort into explaining this phenomenon. However, from the point of view of classical heat engineering, this paradox cannot be explained, and they tried to bashfully hush it up. The impetus for the continuation of the dispute was a somewhat curious story that happened to the Tanzanian schoolboy Erasto Mpemba (Erasto Mpemba) in 1963. Once, during a dessert-making lesson at a cooking school, a boy, distracted by other things, did not have time to cool the ice cream mixture in time and put a solution of sugar in hot milk into the freezer. To his surprise, the product cooled somewhat faster than his fellow practitioners who observed the temperature regime for making ice cream.

Trying to understand the essence of the phenomenon, the boy turned to a physics teacher, who, without going into details, ridiculed his culinary experiments. However, Erasto was distinguished by enviable perseverance and continued his experiments no longer on milk, but on water. He made sure that in some cases hot water freezes faster than cold water.

Entering the University of Dar es Salaam, Erasto Mpembe attended a lecture by Professor Dennis G. Osborne. After graduation, the student puzzled the scientist with the problem of the rate of freezing of water depending on its temperature. D.G. Osborne ridiculed the very posing of the question, stating with aplomb that any loser knows that cold water will freeze faster. However, the natural tenacity of the young man made itself felt. He made a bet with the professor, offering to conduct an experimental test here, in the laboratory. Erasto placed two containers of water in the freezer, one at 95°F (35°C) and the other at 212°F (100°C). What was the surprise of the professor and the surrounding "fans" when the water in the second container froze faster. Since then, this phenomenon has been called the "Mpemba Paradox".

However, to date there is no coherent theoretical hypothesis explaining the "Mpemba Paradox". It is not clear what external factors, the chemical composition of water, the presence of dissolved gases and minerals in it, affect the rate of freezing of liquids at different temperatures. The paradox of the "Mpemba Effect" is that it contradicts one of the laws discovered by I. Newton, which states that the cooling time of water is directly proportional to the temperature difference between the liquid and the environment. And if all other liquids are completely subject to this law, then water in some cases is an exception.

Why does hot water freeze faster?t

There are several versions of why hot water freezes faster than cold water. The main ones are:

hot water evaporates faster, while its volume decreases, and a smaller volume of liquid cools faster - when water is cooled from + 100 ° С to 0 ° С, volume losses at atmospheric pressure reach 15%;
the intensity of heat exchange between the liquid and the environment is the higher, the greater the temperature difference, so the heat loss of boiling water passes faster;
when hot water cools, an ice crust forms on its surface, preventing the liquid from completely freezing and evaporating;
at a high temperature of water, its convection mixing occurs, reducing the freezing time;
gases dissolved in water lower the freezing point, taking energy for crystal formation - there are no dissolved gases in hot water.

All these conditions have been subjected to repeated experimental verification. In particular, the German scientist David Auerbach found that the crystallization temperature of hot water is slightly higher than that of cold water, which makes it possible to freeze the former more quickly. However, later his experiments were criticized and many scientists are convinced that the “Mpemba Effect” about which water freezes faster - hot or cold, can only be reproduced under certain conditions, which no one has been looking for and concretizing so far.

Purified by evaporation, cooling and condensation, the liquid has special physical properties. It is recommended to use it in the heating system, since there are no salts, as well as oxygen. This has a positive effect on the duration of the operation of the equipment.

But many are interested in the question, does distilled water freeze at temperatures below 0˚ C?

It is easy to conduct an experiment at home, and get an answer to this question. We will see that at 0˚ C it will remain liquid. Even if we lower the temperature, its physical state will not change.

So at what temperature does water freeze?

An interesting property of distilled water is observed at a negative temperature. If you lower a piece of ice, snow, air or dust into it, crystals will instantly appear throughout the entire volume.

This is due to the fact that tap water has many centers of crystallization: salts, air inside, the surface of the container, and so on. Purified liquids do not have such centers. Due to this, it can significantly supercool.

The laws of physics say that the more a liquid is purified from impurities, the lower the threshold for the transition to a solid state.

Distilled water freezes at -10˚C and below. This explains its advantage over other coolants during the heating period. Due to this property, when heating a room, it can compete with antifreeze.

At the same time, there are a number of additional advantages over other coolants:

ecological cleanliness;
safety for human life and health;
careful attitude to pipes;
ease of use;
availability.

Now you know that distilled water freezes at temperatures below 10 degrees, so you can be calm about your heating system.

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Have a nice day!

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