Water information!

Water (H2O) is an inorganic substance composed of hydrogen and oxygen, and it is a colorless and odorless transparent liquid at normal temperature and pressure. Water is one of the most common substances, an important resource for all life, including human beings, and the most important component of organisms. Water plays an important role in the evolution of life. Human beings have known about aquatic products for a long time. In the simple material view of ancient China and the West, water is regarded as one of the basic elements and five elements. There was also water in the four-element theory of ancient western countries.

Nature of water

Water is a colorless and odorless transparent liquid at normal temperature and pressure. In nature, pure water is very rare. Water is usually a solution of acid, alkali, salt and other substances, and is still customarily called water. Pure water can be obtained by several distillations with platinum or seasonal utensils. Of course, this is pure water in a relative sense, and it is impossible to be absolutely free of impurities. Water is a substance that can be converted between liquid, gas and solid. Solid water is called ice; The state of gas is called water vapor. When the temperature of steam is higher than 374.2℃, gaseous water cannot be converted into liquid water by pressurization.

At 20℃, the thermal conductivity of water is 0.006 J/s? cm？ K, the thermal conductivity of ice is 0.023 J/s? cm？ K, when the density of snow is 0. 1× 103 kg/m3, the thermal conductivity of snow is 0.00029 J/s? cm？ K at 3.98℃, the maximum density of water is 1× 103kg/m3. When the temperature is higher than 3.98℃, the density of water decreases with the increase of temperature. At 0 ~ 3.98℃, water does not obey the law of thermal expansion and cold contraction, but its density increases with the increase of temperature. At 0℃, the density of water is 0.99987× 103 kg/m3, and the density of ice is 0.9 167× 103 kg/m3. So ice can float on the water.

Water has strong thermal stability. When steam is heated above 2000K, only a small amount of water will be dissociated into hydrogen and oxygen, but water will be dissociated into hydrogen and water when it is electrified. It has great cohesion and surface tension. Except mercury, the surface tension of water is the largest, which can produce obvious capillary phenomenon and adsorption phenomenon. The conductivity of pure water is very weak, but ordinary water contains a small amount of electrolyte and has conductivity.

Water itself is also a good solvent, and most inorganic compounds are soluble in water.

At -2 13. 16℃, water molecules will show hydrophobicity.

The source of water

The earth is the only planet covered with liquid water among the eight planets in the solar system. There are great differences in academic circles about the origin of water on the earth, and there are dozens of different theories of water formation at present. Some people think that in the early days of the earth's formation, hydrogen in the primitive atmosphere was oxidized into water, and water vapor gradually condensed to form the ocean; There is also a view that water originally existed in the nebula material that formed the earth. Another view is that silicate and other substances in the original crust react under the influence of volcanoes and precipitate water. There are also views that comets and meteorites attracted by the earth are the main sources of water on the earth, and even now the water on the earth is still increasing.

Impact on climate

Water can regulate the climate. Water vapor in the atmosphere can block 60% of the earth's radiation and protect the earth from being cooled. Ocean and land water bodies can absorb and accumulate heat in summer, so that the temperature will not be too high; Heat can be released slowly in winter, so that the temperature will not be too low.

Water on the surface of the ocean and the earth evaporates into the sky to form clouds. Water in the clouds falls into the rain through precipitation and turns into snow in winter. Water falling to the surface seeps into the ground to form groundwater; Groundwater gushes out from the stratum again, forming spring water, which flows into the sea through streams and rivers. Form a water cycle.

Precipitation activities such as rain and snow have an important influence on climate formation. In temperate monsoon climate, monsoon brings abundant moisture, forming obvious dry and wet seasons.

In addition, in nature, due to different climatic conditions, water will appear in the form of hail, fog, dew and frost, which will affect the climate and human activities.

Impact on geography

0% of the earth's surface is covered with water. Seen from the sky, the earth is a blue planet. Water erodes rock and soil, scours and silts rivers, transports sediments, builds plains and changes the surface morphology.

The surface water of the earth constitutes the hydrosphere, including oceans, rivers, lakes, swamps, glaciers, snow, groundwater and water in the atmosphere. Because the water injected into the ocean contains a certain amount of salt, and it accumulates and evaporates all the year round, the sea and ocean water are salty and cannot be directly drunk. The water in some lakes is also salty. The largest body of water in the world is the Pacific Ocean. The Great Lakes of North America are the largest fresh water system. The Caspian Sea on Eurasia is the largest saltwater lake.

The volume of water on the earth is about10.36 billion cubic kilometers, of which

Ocean accounts for1320,000,000 cubic kilometers (or 97.2%).

Glaciers and ice sheets account for 25 million cubic kilometers (or 1.8%).

Groundwater accounts for13 million cubic kilometers (or 0.9%).

Freshwater in lakes, inland seas and rivers accounts for 250,000 cubic kilometers (or 0.02%).

Water vapor in the atmosphere accounts for 13 000 cubic kilometers (or 0.05438+0%) at any given time.

Influence on life

Life on earth first appeared in water. Water is an important part of all living things. Water in the human body accounts for 70%; Jellyfish is 98% water. A large number of aquatic plants and other aquatic organisms live in the water.

Water is beneficial to chemical reactions in the body and also plays the role of transporting substances in the living body. Water plays an important role in maintaining the stability of biological body temperature.

Types of water

Different disciplines have different names for water:

According to the different water quality, it can be divided into:

Soft water: Water with hardness below 8 degrees is soft water.

Hard water: water with hardness higher than 8 degrees is hard water. Hard water will affect the effect of detergent, and heating with hard water will have more scale.

According to the content of sodium chloride, drinking water can be divided into:

Fresh water.

salt water

In addition, there are: biological water: water in different States existing in various living systems.

Natural water:

Soil water: Water stored in soil.

Groundwater: Water stored underground.

Ultra-pure water: water with high purity, mostly used in integrated circuit industry.

Crystal water: also known as hydrated water. In crystalline matter, a certain number of water molecules are bound to ions or molecules through chemical bonds.

The chemical formula of heavy water is D2O, and each heavy water molecule consists of two deuterium atoms and one oxygen atom. Heavy water accounts for less than two ten thousandths of natural water, and the heavy water obtained by electrolysis is more expensive than gold. Heavy water can be used as moderator and heat carrier for atomic reactors.

The chemical molecular formula of super heavy water is T2O, and each heavy water molecule consists of two tritium atoms and one oxygen atom. Ultra-heavy water is extremely rare in natural water, and its proportion is less than one billion. The production cost of ultra-heavy water is tens of thousands of times higher than that of water.

The chemical formula of deuterated water is HDO, and each molecule contains one hydrogen atom, one deuterium atom and one oxygen atom. Not very useful.

Water-related chemical reactions

Ionization of water and pH value of solution

Water is a very weak electrolyte, which can ionize weakly: H2O+H2O? H3O++OH- H3O+ is usually abbreviated as H+

Ionic product kw of water = [h+] [oh-]

At 25 degrees, kw =/kloc-0 /×10-14.

pH=-log 10([H+])

PH<7, the solution is acidic, pH=7, the solution is neutral, pH >；; 7. The solution is alkaline.

Water-soluble acidic oxides or basic oxides can react with water to generate corresponding oxyacids or bases. The neutralization reaction between acid and alkali produces salt and water. Under the action of electric current, water can be decomposed into hydrogen and oxygen. Alkali metals will burn when exposed to water.

Under the action of catalyst, inorganic matter and organic matter can be hydrolyzed with water;

Hydrolysis of organic matter: some atoms or groups in organic matter molecules are replaced by hydrogen atoms or hydroxyl groups (-OH) of water molecules, such as methyl acetate hydrolysis;

Hydrolysis of inorganic substances: usually hydrolysis of salts, such as sodium acetate, a weak acid salt, which combines with H+ in water to form a weak acid, making the solution alkaline;

In addition, water itself can also be used as a catalyst.

Problems and Countermeasures of Shortage of Freshwater Resources

The total water reserve on the earth is about1.36x1kloc-0/8m3, but only 2.5% of it is fresh water except the salt water resources such as the ocean. Fresh water mainly exists in the form of glaciers and deep groundwater, and the fresh water in rivers and lakes accounts for only 0.3% of the total fresh water in the world.

The World Meteorological Organization pointed out at the beginning of 1996 that water shortage is the primary problem facing cities all over the world. It is estimated that by 2050, 46% of the urban population in the world will be short of water. For areas lacking water resources, water has surpassed the category of biological resources and become a strategic resource. Because of the scarcity of water resources, the possibility of water war is getting higher and higher.

In order to make the whole world care about the shortage of fresh water resources, the 47th United Nations General Assembly designated March 22nd as World Water Day.

Utilization of water

Water is an important resource for human life, especially for agricultural irrigation, and the origin of human civilization is mostly in the big river basin. Early cities were generally built near the water to solve the problems of irrigation, drinking water and sewage. In human daily life, water plays an indispensable role in drinking, cleaning and washing.

With the development of science and technology, people build water conservancy projects to fight against natural disasters such as floods and waterlogging. Therefore, some special research fields related to water have been formed, such as hydraulics, hydrological science, water treatment and so on. , and even has produced water-based industrial aquaculture.

This cheap raw material is widely used in industrial production and chemical production. However, the arbitrary discharge of untreated wastewater will cause water pollution. In order to solve this problem, sewage treatment becomes very necessary. (See Water Pollution and Sewage Treatment. )

Development of water and agriculture

In 3000 BC, China

The oldest known irrigation technology is used for rice cultivation. The farmer built a rice field, surrounded by dams, similar to a shallow pond, and then drew water from a nearby stream and poured it into it. This ancient technology is still widely used in Southeast Asia, East Asia and South Asia.

In 2000 BC, Egypt

Farmers in Egypt invented a way to get water from the Nile. The tool they use is called orange juice, which is to lift the bucket from the river conveniently with a horizontal bar. Water from the river irrigates farmland through canals. This orange is still used in Egypt, India and some other countries.

In 700 BC, Assyria

Assyria is a country in the ancient East. Its king, Senna Shirley, planted fruit trees, cotton and other rare plants around the capital Nineveh. In order to irrigate these plants, he built a canal 10 km long and a stone trough to get water from the nearby mountains.

In 500 AD, Mexico

There are many swamp lakes around Tenoch, the former Mexican capital, in which the Aztecs built terraces. They spread the fertile soil at the bottom of the lake on terraces and planted corn. Netted ditches around OTA ensure water for crops, and farmers can also sail through OTA.

Us ad 1870

Agricultural water in the arid Great Plains of the central United States can only rely on groundwater. When the settlers who have allocated all government land come there, they use the power of windmills to extract groundwater, then dig ditches and introduce the extracted groundwater into farmland for irrigation.

Israel, A.D. 1990

Water is the basis of survival in desert areas. Drip irrigation is an irrigation method in which a small hole is made in the water pipe and water is directly dripped into the soil next to the root of each plant. This method can minimize the loss of irrigation water.

Treatment of drinking water

1. First filtration: the water flow introduced from rivers and other places is filtered through a filter screen to remove fish, leaves and garbage;

2. Adsorption: Alum is added into the water filtered for the first time to form viscous flocs, and particles such as soil and bacteria are attached to the alum flowers, and then the water flows through the sedimentation tank to filter out the alum flowers;

3. Second filtration: water slowly flows through sand or gravel to filter out algae, bacteria and some chemical components;

4. Chlorination: adding chlorine to water to kill residual organic organisms;

5. Ventilation: forcing air into the treated water to drive away the gas generated by chlorine and reduce unpleasant smell and taste;

6. Additional treatment: Sodium or lime can be added to soften hard water. Some communities add fluoride to prevent chlorine from corroding teeth.

(domestic) wastewater treatment

1. Primary treatment: When wastewater flows through the treatment equipment, the flow rate slows down and some large solids settle down. When water passes through the sedimentation tank, smaller particles sink to the bottom to form mud;

2. Re-treatment: In the trickling filtration system, the wastewater is filtered by gravel, and the surface of the gravel can be covered with a layer of bacterial community to decompose the waste in the sewage;

3. Additional treatment: Water is discharged into the open-air pond, where it is naturally purified by sunlight and air. After entering the atmosphere, pure water vapor is formed. Chlorine is usually added before treated water is discharged again.

Water in ancient world view

In the early days of civilization, people began to explore the composition or classification of various things in the world, in which water played an important role. The four elements put forward by the ancient west said that there was water; There are also water in the four major Buddhists; In China's ancient theory of five elements, water represents all liquids and things with flowing, moist and feminine properties.

Water worship

In human childhood, water has the ability to nurture and destroy, and its unpredictable temperament produces feelings of love and fear, which leads to water worship. By endowing water with the spirit of God, we pray that water can bring peace, harvest and happiness to mankind.

The traditional Dragon King in China deified water. Where there is water, there is the Dragon King, whose temples and churches are all over the country. Sacrificing the Dragon King and praying for rain are traditional beliefs and customs in China.

And colloquialism

Describe people who are not ambitious or do things well enough.

For example, that's how you mix water. You are so bad at it. )

High mountains and Running water

Guqin music During the Warring States Period, there was a story of Qin Le about high mountains and flowing water, so it was also said that "high mountains and flowing water" was written by Boya. The music score was first seen in The Secret Music of the Ming Dynasty (written by Zhu Quan at 1425). The solution of this score is: "Mountain Flowing Water is two songs, but there is only one. The first ambition is to care about mountains and rivers, saying that benevolent people are Leshan. The ambition of the future is to care about running water, which means that the wise are happy with water. The Tang dynasty is divided into two songs, regardless of section. The highest mountain is divided into four sections and eight sections of flowing water. " For more than 2,000 years, two famous guqin songs, Mountain and Running Water, together with the story of Boya guqin meeting a bosom friend, have been widely circulated among the people.

"Mountain Flowing Water" takes "Boya Guqin meets a bosom friend" as the main line, and there are many kinds of Le Shu. There are two kinds of Qin music and Zheng music, both of which have the same name and different styles.

With the development of Qin's performing arts since Ming and Qing Dynasties, "mountain" and "water" have undergone great changes. The legendary secret score is not segmented, but later the piano score is segmented. Among the numerous music scores since Ming and Qing Dynasties, Running Water, which was adapted by Zhang Kongshan, a pianist of Sichuan School, was included in Tian Wen Song Score (1876) compiled by Tang Dynasty in Qing Dynasty. The sixth paragraph of the technique of "rolling, brushing, dialing and noting", also known as "seventy-two rolling and brushing water", is widely used because of its vivid image and blending of scenes. According to the Qin family's textual research, before the publication of Tianwenge's piano score, there was no sixth paragraph played by Zhang Kongshan in all the scores, and the whole song had only eight paragraphs, which was consistent with the solution of the magical secret score, but Zhang Kongshan passed it on. I'm Yan Xin? Oh, danger, are you like a seed?

There is also a guzheng song "Mountain Stream and Running Water", the music is quite different from piano music, and it is also based on "Boya Guqin meets a bosom friend". There are many genres of music books. The most widely circulated and influential is the Biography of Zhejiang Wulin School, with elegant melody and meaningful charm, which has the appearance of "majestic mountains and flowing water".

Lu Pai's "Mountain Flowing Water" is an ensemble of four ditties: Qin Yun, the wind shaking the bamboo, the bell ringing at night and the rhyme, also known as four paragraphs and four paragraphs of brocade.

The Mountain Flowing Water of Henan School is based on the folk song Old Liu Ban, with a fresh and lively rhythm. Folk artists often play this song when they meet for the first time to show respect and make friends. There is no * * in common between the three and the guqin song "Mountain Flowing Water", and they are all different songs with the same name.

General regulations

It is said that Boya, a pianist in the pre-Qin period, once played the piano on a barren land, but Zhong Ziqi, a woodcutter, can understand that this is a description of "ambition in the mountains" and "running water with ambition". Boya was surprised and said, "Well, my son's heart is with me." After the death of the hippo chef, Boya lost her bosom friend, her piano broke and she didn't exercise for life, so there was a song of mountains and flowing water.

During the Spring and Autumn Period, there was a man named Yu Boya, who was proficient in temperament and superb in piano skills. He was a famous pianist at that time. When Yu Boya was young, he was smart and eager to learn. He has learned from others and his piano skills have reached the level. But he always feels that he can't express his feelings about all kinds of things in a superb way. Boya's teacher knew his idea and took him to Penglai Island in the East China Sea by boat, so that he could enjoy the natural scenery and listen to the waves of the sea. Boya looked up and saw the waves surging and splashing; Seabirds are roaring and singing; The lush trees in the forest are like entering a fairyland. A wonderful feeling arises spontaneously, as if the harmonious and beautiful music of nature rises in my ear. He couldn't help playing the piano, his voice turned at will, and the beauty of nature was integrated into the sound of the piano. Boya experienced an unprecedented realm. The teacher told him, "You have learned."

One night boating in Boya. Facing the cool breeze and bright moon, he was full of thoughts, so he played the piano again, and the sound of the piano was melodious and getting better. Suddenly I heard someone screaming on the shore. When Boya heard the sound, he got out of the boat and saw a woodcutter standing on the shore. Knowing that the man was a bosom friend, he immediately invited the woodcutter aboard and played for him with great interest. Boya played a tune praising the mountains, and the woodcutter said, "How wonderful! Majestic and solemn, such as Mount Tai towering into the clouds! " When he played the surging waves, the woodcutter said, "How wonderful! Vast and boundless, it seems to see rolling water and boundless sea! " Boya was excited and said excitedly, "bosom friend!" You are really my bosom friend. "This woodcutter is Zhong Ziqi. Since then, the two have become very good friends.

One of the five elements. Kidney belongs to water in the five elements, so it is often called kidney water. In addition, it is also used to refer to the name of the disease or the pathological mechanism of edema disease.

Oxyhydrogen compounds. The chemical formula is H2O. In nature, there is little pure water, and water is usually a solution of polybasic acid, alkali, salt and other substances. Pure water is distilled many times with platinum or seasonable utensils. Water is a substance that can be converted between liquid, gas and solid. The conversion conditions are temperature and pressure. At standard atmospheric pressure, the freezing point of water is 0℃ and the boiling point is 100℃. When the temperature of water vapor is higher than 374.2℃, gaseous water cannot be converted into liquid water. The specific heat capacity of liquid water is 4. 18 Joule/(g-Celsius), and that of ice is about 2.09 Joule/(g-Celsius). At 1 standard atmospheric pressure and 100℃, the heat of vaporization of water is 2253.02 Joule/g, and at normal temperature and pressure, it is 244 1. 12 Joule/g. When water vapor condenses into liquid water, the same heat is released. At 0℃ and 1 standard atmospheric pressure, the heat of fusion of ice is 333. 146 Joule/g, and the same heat is released when water condenses into ice. The heat absorbed when water directly changes from solid to gas is called sublimation heat, which is equal to the sum of vaporization heat and heat of fusion. At 20℃, the thermal conductivity of water is 0.006 Joule/(sec. Centimeter. Celsius), the temperature of ice is 0.023 Joule/(second. Centimeter. Celsius), and the thermal conductivity of snow is 0.00029 Joule/(second. Centimeter. When the density of snow is 0. 1 kg/l, the maximum density of water is 65438 0 kg/l at 3.98℃. When the temperature is higher than 3.98℃, the density of water decreases with the increase of temperature. When the temperature is 0 ~ 3.98℃, the density of water increases with the increase of temperature. At 0℃, the density of water is 0.99987 kg/L, and the density of ice is 0.9 167 kg/L. The thermal stability of water is very strong. When water vapor is heated above 2000K, only a small part is dissociated into hydrogen and oxygen. Any water-soluble acidic oxide or alkaline oxide can react with water to generate corresponding oxyacid or alkali. The conductivity of pure water is extremely weak. The acidity and alkalinity of water is expressed by pH value, and the pH value of natural water is 6.8 ~ 8.5. Water has great cohesion and surface tension. Except for mercury, the surface tension of water is the largest, which can produce capillary phenomenon and adsorption phenomenon.

Water can regulate the climate. Water vapor in the atmosphere can block 60% of the earth's radiation and protect the earth from being cooled. Ocean and land water bodies can absorb and accumulate heat in summer, so that the temperature will not be too high, and heat can be released slowly in winter, so that the temperature will not be too low. Water erodes rock and soil, scours and silts rivers, transports sediments, builds plains and changes the surface morphology. Water brings life to the earth. It is the main component of all living things. There are about 65.438+065.438+02 billion tons of water in the world's animals and plants and 4 billion people. Human society depends on water for survival and development. In ancient times, human beings used water to avoid harm and adapt to water to survive; In modern times, mankind started water, built projects, developed water conservancy and controlled floods; Since modern times, with the development of society and production, the available water resources on the earth have become increasingly scarce, and water bodies have been polluted, which has seriously affected the living environment of human beings. Humans gradually realize that water is an important resource and environmental factor, so they start new activities to promote water and avoid harm at a higher level.

1At the beginning of 996, the World Meteorological Organization pointed out that water shortage is the primary problem facing cities all over the world. It is estimated that by 2050, more than two-thirds of the world's population will live in cities, and 46% of the world's urban population will be short of water. It is necessary to balance the relationship between social and economic development and urban fresh water supply management, and carry out large-scale engineering construction of water resources storage, transportation and management.

water

① The name of the disease, namely edema. Edema is mainly manifested as water-liquid metabolic disorder, hence the name. Su Wenping's theory of meteorology: "neck pulsation, wheezing and coughing are called water." The eyes are slightly swollen like lying silkworms, like water. " Then he said, "My shin is swollen with water."

② refers to the pathological mechanism of edema disease. Su Wen's Theory of Differentiation of Yin and Yang: "The knot of three yin is the water." Bing Wang's note: "Three yin knots mean that the veins of spleen and lung are cold knots, and the spleen and lung are cold knots, then they are vaporized into water."

③ One of the five elements. Su Wen Dirty Qi Law: "The five elements are Jin Mu's fire, water and earth." Kidney belongs to water in the five elements, so it is often called kidney water.

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Water is the general name of posts with little value on the forum. Every such post is called "Shuigang", the act of posting Shuigang is called "irrigation", and some posts with many posts and all Shuigang are called "Shuilou", which often occupies a position called "diving". Some forums like to post more posts and encourage irrigation, but academic forums generally prohibit irrigation.

There are two kinds of water pollution: one is natural pollution; The other is man-made pollution. At present, man-made pollution is the most harmful to water bodies. Water pollution can be divided into three categories: chemical pollution, physical contamination and biological pollution.

chemical pollution

Water pollution caused by chemical impurities. According to the specific pollution impurities, chemical pollution can be divided into six categories:

(1) Inorganic pollutants: Inorganic pollutants that pollute water bodies include acids, alkalis and some inorganic salts. Acid-base pollution changes the pH value of water, hinders the self-purification of water, corrodes ships and underwater buildings, and affects fisheries.

(2) Inorganic toxic substances: Inorganic toxic substances that pollute water bodies are mainly substances with potential long-term effects such as heavy metals, mainly elements such as mercury, cadmium, lead and arsenic.

(3) Organic toxic substances: The organic toxic substances that pollute water bodies are mainly various organic pesticides, polycyclic aromatic hydrocarbons and aromatic hydrocarbons. Most of them are synthetic substances with stable chemical properties, which are difficult to be biodecomposed.

(4) Aerobic pollutants: Organic substances such as carbohydrates, protein, fats, phenols and alcohols contained in domestic sewage and some industrial wastewater can be decomposed by microorganisms. In the process of decomposition, a lot of oxygen is needed, so it is called aerobic pollutant.

(5) Plant nutrients: mainly plant nutrients such as nitrogen and phosphorus in domestic and industrial sewage, and residual nitrogen and phosphorus in farmland drainage.

(6) Oil pollutants: mainly refer to the pollution of water by oil, especially the pollution caused by offshore oil production and tanker accidents.

Physical contamination

Physical contamination includes:

(1) suspended matter pollution: suspended matter refers to insoluble matter contained in water, including solid matter and foamed plastics. They are caused by the leakage of domestic sewage, garbage and waste from mining, quarrying, construction, food processing and paper making into water or farmland soil erosion. Suspended matter affects the appearance of water, hinders the photosynthesis of plants in water and reduces the dissolution of oxygen, which is unfavorable to aquatic organisms.

(2) Thermal pollution: If the cooling water produced by various industrial processes is not directly discharged into the water body, it may lead to an increase in water temperature, a decrease in dissolved oxygen content, and an increase in the toxicity of some toxic substances in the water, thus endangering the growth of fish and aquatic organisms.

(3) Radioactive pollution: Due to the development of atomic energy industry, the exploitation of radioactive mineral deposits, the establishment of nuclear tests and nuclear power plants, and the application of isotopes in medicine, industry, scientific research and other fields, radioactive waste water and waste have increased greatly, causing certain radioactive pollution.

biological pollution

Domestic sewage, especially hospital sewage and some industrial wastewater, often brings in some pathogenic microorganisms after polluting water bodies. For example, some pathogenic bacteria, such as typhoid fever, paratyphoid fever and cholera bacteria, which originally existed in human and animal intestines, can enter the water body through the pollution of human and animal feces and spread with the water flow. Some viruses, such as hepatitis virus and adenovirus, are often found in polluted water. Some parasitic diseases, such as amebic dysentery, schistosomiasis and leptospirosis, can also be transmitted by water. Preventing water pollution by pathogenic microorganisms is also an important issue to protect the environment and human health.