Water

For water in its solid state, see ice.

For water in its gas state, see Water vapor.

Water (H₂O) is a simple chemical compound made of two hydrogen atoms and one oxygen atom. It is clear, has no taste or smell, and is almost colorless. All living things need water to survive. Water molecules stick together because of hydrogen bonds. These bonds give water special properties. For example, water has high surface tension, and can dissolve many substances. Water exists in three forms on Earth: solid (ice), liquid (water), and gas (water vapor). The word "water" comes from the Old English word wæter.

Water (H2O)
IUPAC name	water, oxidane
Other names	Hydrogen hydroxide (HH or HOH), hydrogen oxide, dihydrogen monoxide (DHMO) (systematic name), hydrogen monoxide, dihydrogen oxide, hydric acid, hydrohydroxic acid, hydroxic acid, hydrol, μ-oxido dihydrogen, κ1-hydroxyl hydrogen(0)
Identifiers
CAS number	7732-18-5
PubChem	962
ChEBI	CHEBI:15377
RTECS number	ZC0110000
SMILES	O
Beilstein Reference	3587155
Gmelin Reference	117
Properties
Molecular formula	H2O
Molar mass	18.01528(33) g/mol
Appearance	White crystal-like solid, almost colorless liquid with a hint of blue, colorless gas
Odor	None
Density	Liquid: 0.9998396 g/mL at 0 °C 0.9970474 g/mL at 25 °C 0.961893 g/mL at 95 °C Solid: 0.9167 g/ml at 0 °C
Melting point	0.00 °C, 273 K, 32 °F
Boiling point
Solubility in water	N/A
Solubility	Poorly soluble in haloalkanes, aliphatic and aromatic hydrocarbons, ethers. Improved solubility in carboxylates, alcohols, ketones, amines. Miscible with methanol, ethanol, propanol, isopropanol, acetone, glycerol, 1,4-dioxane, tetrahydrofuran, sulfolane, acetaldehyde, dimethylformamide, dimethoxyethane, dimethyl sulfoxide, acetonitrile. Partially miscible with Diethyl ether, Methyl Ethyl Ketone, Dichloromethane, Ethyl Acetate, Bromine.
Vapor pressure	3.1690 kilopascals or 0.031276 atm
Acidity (pKa)	13.995
Basicity (pKb)	13.995
Thermal conductivity	0.6065 W/(m·K)
Refractive index (nD)	1.3330 (20 °C)
Viscosity	0.890 cP
Structure
Crystal structure	Hexagonal
Point group	C2v
Molecular shape	Bent
Dipole moment	1.8546 D
Thermochemistry
Std enthalpy of formation ΔfHo298	−285.83 ± 0.04 kJ/mol
Standard molar entropy So298	69.95 ± 0.03 J/(mol·K)
Specific heat capacity, C	75.385 ± 0.05 J/(mol·K)
Hazards
Main hazards	Drowning Avalanche (as snow) Water intoxication (see also Dihydrogen monoxide parody)
NFPA 704	0 0 0
Flash point	Non-flammable
Related compounds
Other cations	Hydrogen sulfide Hydrogen selenide Hydrogen telluride Hydrogen polonide Hydrogen peroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Water in three states: liquid (including the clouds, which are aerosols), solid (ice) and gas (water vapour)

About 71% of Earth’s surface is covered by water. Most of this water (about 97%) is in the oceans. This water is salt water, which we cannot drink or use for farming. Only 3% of Earth’s water is fresh water, and even that is not easy to get. 69% of all fresh water is frozen in glaciers and ice caps. 30% is stored underground in aquifers. Less than 1% is in lakes, rivers, and swamps. If you look at all the water on Earth, only about 1% can be used by us. And most of that water is found underground. Water is always moving in a cycle. This is called the water cycle. It includes:

• Evaporation (water turns into vapor),
• Transpiration (plants release water vapor),
• Condensation (vapor forms clouds),
• Precipitation (rain or snow falls),
• Runoff (water returns to oceans and lakes).

Water has many unique abilities. One is that it expands when it freezes. This makes ice less dense than liquid water, so ice floats. Water also has a high specific heat capacity. Water also has a high specific heat. It can absorb or lose a lot of heat without changing temperature much. This helps keep Earth's climate stable. Water’s surface tension lets it form droplets. It also lets small insects walk on water. Water is an excellent solvent. It can dissolve more substances than any other liquid. This is why it is called the "universal solvent." However, it cannot dissolve oily or nonpolar substances well. These special abilities come from water's polar nature and the hydrogen bonds between them.

Water is important for all living things. Every kind of life we know needs water to survive. This includes tiny living things like bacteria, archaea, and protists, and bigger ones like fungi, plants and animals. The human body is about 50-60% water. Water helps move nutrients, gases, and waste inside the body. Inside cells, water is where most chemical reactions happen. It also helps cells keep their shape. Water is needed for digestion in animals, and photosynthesis in plants. It also helps control body temperature. Without water, life could not exist. That is why water is one of the most important substances for all living things.

Water is also very important to the world economy. About 70% of the fresh water people use goes to farming. Water is used to grow crops and raise animals. Fish from oceans, lakes, and rivers are an important source of food. Many products, like crude oil and other goods, are moved around the world by ships through oceans, rivers, and canals. Water is also used to heat and cool buildings and machines. Because it can dissolve many substances, it is very useful in factories, cooking, and cleaning. Water can also be used to make electricity, in hydroelectric plants. It is also used for fun activities like swimming, boating, fishing, diving, ice skating, snowboarding, and skiing.

Many civilizations in history began near rivers or other places where they could get water easily. For example, Mesopotamia began between the Tigris and Euphrates rivers. Ancient Egypt depended on the Nile. The Indus Valley civilization started near the Indus River. Ancient Rome was built near the Tiber River. Even today, many big cities like London, New York, and Shanghai grew near water. Being close to rivers or oceans made it easier to trade and travel. Islands with good harbors, like Singapore, also became rich and powerful because ships could stop there easily. In dry places like North Africa and the Middle East, clean water has always been important. Having water often made the difference between a small village and a strong civilization.

Water is not just found on Earth. Scientists have discovered water in many places in space. Ice has been found on Mars, and even on the Moon. Some moons in our solar system, like Europa and Ganymede (around Jupiter), and Enceladus (around Saturn) may have liquid water under their icy surfaces. Water vapor has also been found in the atmosphere of some exoplanets. These are planets that orbit stars far away from our solar system. Water has even been found in clouds of gas and dust in space where new stars are being born.

On Earth

A graphical distribution of the locations of water on Earth

Visualisation of the distribution of water on Earth (by volume). Each tiny cube (such as the one representing biological water) corresponds to approximately 1,000 km³ of water. This amount of water has a mass of about 1 trillion tonnes (200,000 times that of the Great Pyramid of Giza or five times that of Lake Kariba, arguably the heaviest man-made object). Comprising 1 million tiny cubes, the entire cube would measure about 1,102 km on each side.

Hydrology is the science that studies how water moves, where it is found, and its quality all over the Earth. It is part of a larger group of sciences that study water in different places and forms:

• Hydrography studies where water is located on Earth's surface.
• Hydrogeology focuses on groundwater, water stored underground.
• Glaciology studies ice and glaciers.
• Limnology looks at inland water bodies like lakes and rivers.
• Oceanography studies the oceans.
• Ecohydrology explores how water interacts with ecosystems and living things.

All the water on Earth (in oceans, rivers, lakes, ice, underground, and even in the air) is called the hydrosphere. The Earth holds about 1.386 billion cubic kilometers of water. Water on Earth is not distributed equally. Most of the water on Earth is found in the oceans. About 96.5% of all the water on Earth is salt water in the oceans. This cannot used for drinking or farming. That leaves only 2.5% of the Earth's water as fresh water. Of this small percentage of freshwater, most of them are in hard to reach places. Around 68.7% of Earth's fresh water is stored in ice caps, glaciers, and permanent snow. This is mainly in Antarctica and Greenland. Another 30.1% is found as groundwater, stored in aquifers deep under the Earth's surface. This groundwater is an important source of water for wells and springs. It is very important in agriculture and for drinking. Only about 1.2% of all fresh water is water that can be found on the surface of the Earth. This includes water in lakes (about 20.9%), swamps and marshes (2.6%), and rivers (0.49%). Water can also be found in the atmosphere as vapor, clouds, and precipitation, and in soil moisture, permafrost, and living organisms. But these make up only a tiny fraction of all the water on Earth (less than 0.01%).

Fresh water is not evenly distributed across the Earth. Some places have more water than others. Countries like Canada, Brazil, and Russia have large supplies of fresh water because of lots of rivers and rainfall. In contrast, dry places like North Africa, the Middle East, and parts of Central Asia have very limited freshwater. Some tropical and temperate regions get lots of rainfall, while others may go months without much rain.

Water plays a big role on Earth. It helps break down rocks through weathering. It moves soil and sediments through erosion. It helps form layers of sedimentary rock over time. Deep inside the Earth, water helps create magma, which leads to volcanoes, especially where tectonic plates meet.

Properties of water

A water molecule consists of two hydrogen atoms and one oxygen atom.

Water is a chemical substance. It is made of two hydrogen atoms and one oxygen atom. These atoms are held together by something called a covalent bond. At room temperature and normal pressure, water is a liquid. It has almost no color, taste or smell. Water is often called the "universal solvent" because it can dissolve more substances than any other liquid. But it cannot dissolve nonpolar substances like oil very well. Water is also the only common material on Earth that can naturally exist as a solid, liquid, and gas.

Hydrogen bonds

Tetrahedral structure of water

Hydrogen bonds between molecules of water

A water molecule is made of two hydrogen atoms and one oxygen atom. Its chemical formula is H₂O. The shape of a water molecule looks like a bent "V". The angle between the hydrogen atoms is about 104.5°. This shape happens because the oxygen atom has two pairs of extra electrons. These push the hydrogen atoms closer together. This can be seen in the picture above. Oxygen pulls on electrons more strongly than hydrogen does. So, when oxygen and hydrogen share electrons in a water molecule, the electrons spend more time near the oxygen atom. This makes the oxygen side of the molecule slightly negative and the hydrogen side slightly positive. Because of this, water is called a polar molecule. This polarity lets water molecules to stick to each other using hydrogen bonds. These are weak bonds. They form between the positive side of one water molecule and the negative side of another.

Water is special because it stays as a liquid at room temperature. That might not seem surprising until you compare it to similar substances. Take hydrogen sulfide (H₂S), for example. It is like water, but it has sulfur instead of oxygen. Even though ydrogen sulfide is heavier than water, it is a gas at room temperature. The reason water stays a liquid is because of hydrogen bonds. These weak bonds help water molecules stick together. They are not as strong as covalent bonds. But they are strong enough to make water act in very interesting ways.

Cohesion and adhesion

Water beading on a leaf

Water striders walk on water because of surface tension

Water molecules stick to each other. This is called cohesion. Inside a drop of water, each molecule is pulled in all directions by the other water molecules around it. These pulls are balanced, so the water molecule stays still. But at the surface, there are no water molecules above. So the molecules at the top are only pulled from the sides and below. This creates a strong pull inward, which makes the surface act like a stretched skin. This is called surface tension. Surface tension is why water forms round drops. It is also why small insects, like water striders, can walk on water.

When water sticks to other materials, like the side of a glass, it is called adhesion. Whether water forms flat puddles or round beads depends on the balance between cohesion and adhesion. If water sticks more to the surface, it spreads out. If water sticks more to itself, it forms beads. Because of surface tension, water droplets naturally become round. A sphere is the shape with the smallest surface area for a given volume. Since surface tension tries to shrink the surface area, droplets become almost spherical. This is a way for water to use the smallest amount of energy. Because water molecules at the surface have more energy than the ones inside. So by making the surface smaller, there are less water molecules at the surface.

When water climbs up a thin tube or material, it is called capillary action. You can see this when you dip the end of a piece of toilet paper in water. The water slowly climbs up the toilet paper. In plants, capillary action helps water move from the roots to the leaves. As water evaporates from the leaves, it pulls more water up behind it. Adhesion helps the water stick to the sides of the plant's tubes. Cohesion keeps the water molecules connected like a chain, so they move upward together. This allows them to move up against gravity.

Heat and water

The oceans can store heat helping to keep Earth's temperature stable

Water is very at staying at the same temperature. It does not heat up or cool down quickly. This is because water has a high specific heat capacity. That means it takes a lot of heat to make water warmer, and it cools down slowly too. Specific heat is the amount of heat needed to change the temperature of 1 gram of a substance by 1°C. For water, this is 1 calorie. That is more than most other substances. For example, alcohol only needs 0.6 calories to do the same, so it heats up faster than water.

If you touch a metal pot with warm water inside, the metal might feel hotter than the water. That is because metal heats up faster. Water takes longer to warm up because energy is first used to break the hydrogen bonds between water molecules. Once those bonds are broken, the molecules can move faster, and the temperature rises. When water cools down, the hydrogen bonds form again and release heat. This helps keep temperatures steady. Oceans and lakes can absorb heat from the sun during the day or in summer and release it slowly at night or in winter. That is why places near water usually have milder temperatures. Water’s high specific heat also keeps the ocean from getting too hot or too cold. This is very important for ocean life. And because our bodies are mostly made of water, this also helps us keep a steady body temperature.

Water molecules usually stay close together. But if some molecules move fast enough, they can break free and escape into the air as gas. This process is called evaporation. Even at low temperatures, the fastest molecules can still escape. This is why a glass of water will slowly disappear over time. Heating water makes its molecules move faster, so it evaporates faster too. The heat of vaporization is the amount of heat needed to turn 1 gram of liquid water into gas. For water, it takes about 580 calories to evaporate just 1 gram at 25°C. This is nearly double the amount needed for ammonia and alcohol. Water’s high heat of vaporization is because of its strong hydrogen bonds. Breaking those bonds takes a lot of energy.

This high heat of vaporization has important effects on Earth. Tropical oceans take in a lot of heat from the Sun. Some of this heat is used to evaporate water. When that water vapor travels to cooler places and turns back into rain, it releases heat. This helps balance Earth’s climate and spread heat around the planet. Evaporation also cools things down. When water evaporates, the fastest (hottest) molecules leave first. This lowers the temperature of the water that is left behind. This is called evaporative cooling. It helps keep lakes, plants, and animals from getting too hot. When we sweat, the sweat takes heat from our skin as it evaporates. This is why sweating cools down. On hot, humid days, the air already has a lot of water vapor. That makes it harder for sweat to evaporate, so we feel even hotter. Some animals that cannot sweat, like elephants, cool themselves by spraying water on their skin.

It also takes a lot of energy to melt ice. This is called the heat of fusion. For example, the same amount of energy needed to melt ice could warm that same ice from –160 °C all the way up to 0 °C. The hydrogen bonds need to be broken first. This is why ice melts slowly. In nature, this helps ice last longer. Before we had refrigerators, people used ice to keep food cool because it stayed frozen for a long time.

Density of ice

Iceberg floating on water

Water is one of the only substances that becomes less dense when it freezes. This means that ice floats on water. Most substances get smaller and denser when they freeze. But water is different. It expands (or gets bigger) when it freezes. This strange behavior happens because of hydrogen bonds. At temperatures above 4°C, water acts like most liquids. It expands when heated and shrinks when cooled. But between 4°C and 0°C, something strange happens. As the water gets colder, the molecules slow down. They do not have enough energy to break the hydrogen bonds between them. At 0°C, the molecules line up into a solid crystal shape. Each molecule connects to four others with hydrogen bonds. These bonds hold the molecules further apart. So the ice takes up more space than the liquid water, even though it has the same number of molecules. That is why ice is about 10% less dense than water at 4°C. When ice melts, the bonds break and the molecules move closer together. Water is densest at 4°C. It becomes less dense if it gets warmer or cooler from that temperature.

The fact that ice floats is very important for life on Earth. If ice sank, lakes and oceans could freeze all the way to the bottom. This would make it hard or even impossible for fish and other living things to survive. Instead, ice floats on top, and acts like a blanket. This helps keep the water below from freezing. Fish and other organisms can stay alive under the ice. Also, floating ice provides homes for animals like polar bears and seals.

Water as a universal solvent

Sodium ion from salt dissolved in water

When you drop a sugar cube into a glass of water, the sugar slowly dissolves and spreads out. This creates a mixture. This type of mixture is called a solution. In a solution, the solvent is the substance that does the dissolving (in this case, water), and the solute is the substance that gets dissolved (the sugar). If water is the solvent, the solution is called an aqueous solution.

Water is a very good solvent. Because of this, it is often called the "universal solvent". This is because it can dissolve more substances than any other substance. This happens because water molecules have slightly positive and negative parts. These parts attract other charged or polar substances. For example, when you add salt (sodium chloride, or NaCl) to water, it breaks into sodium (Na⁺) and chloride (Cl⁻) ions. The negative side of water pulls on the sodium, and the positive side pulls on the chloride. Water molecules surround each ion. They then pull them away from the salt crystal. After that, they spread them out in the water. This group of water molecules around an ion is called a hydration shell. Other ionic compounds, like potassium chloride, also dissolve in water this way. Seawater is full of dissolved ions like these. But a substance does not have to be made of ions to dissolve in water. Polar molecules like sugar can also dissolve. This is because they can form hydrogen bonds with water. Even large molecules, like proteins, can dissolve in water if they have polar or charged areas on their surfaces.

Water is the main solvent for living things. Many important substances are dissolved in the water in blood, plant sap, and cells. Any substance that mixes well with water is called hydrophilic (water-loving). Some hydrophilic substances do not dissolve in water. For example, some molecules in cells are too big to dissolve. Another example is cotton. Cotton is made up of giant molecules of cellulose. Cellulose does not dissolve in water. It has lots of positive and negative parts that can form hydrogen bonds with water. Water sticks to the cellulose. That is why cotton towels drys things well, but does not dissolve in the washing machine. Plants also use cellulose in the tubes that carry water from roots to leaves. Water sticks to the hydrophilic walls of these tubes, helping it move upward against gravity. On the other hand, substances that do not mix with water are called hydrophobic (water-fearing). These include oils and fats. They don’t dissolve because they do not have charges that attract water. That is why oil and water do not mix. Hydrophobic molecules can be found in cell membranes. Without them, cells would dissolve in water. Life would be impossible.

States of water

The three common states of matter

Water can exist in three main forms: solid, liquid, and gas. These are called states or phases. Which one water is in depends on the temperature and pressure.

When people say "water" in everyday life, they usually mean liquid water. This is the form that comes from taps, fills oceans, rivers, and lakes, and is used for drinking, cooking, and cleaning. Liquid water is the most common form found on Earth's surface. When water gets cold enough, it freezes and becomes a solid called ice. Ice can be in the form of hard cubes (like in your freezer) or soft, loose crystals, like snow. There are also other strange kinds of ice. These are often found in extreme environments like outer space deep inside Uranus. When water gets hot enough, it turns into a gas called water vapor. This is what we see as steam rising from boiling water.

Water can also exist in a very strange state called a supercritical fluid. This only happens at extremely high temperatures above (374°C or 705°F) and very high pressures (above 22.064 megapascals). Here, water acts like a gas and a liquid at the same time. It can flow like a liquid and spread out like a gas. Supercritical water is useful because it can dissolve many things that normal water cannot. It can dissolve nonpolar organic compounds like oil. This strange state of water does not happen naturally on Earth’s surface. But it can happen deep in the ocean. One example is near hydrothermal vents. This happens at around 2200 meters deep. The ocean is much deeper than that on average at about 3800 meters.

Changing states

Phase diagram of water

Water as a solid, liquid and gas at the same time

A phase diagram is a special graph. It shows how a substance like water changes between solid, liquid, and gas depending on the temperature and pressure. On this graph, the bottom (horizontal) line shows temperature. The side (vertical) line shows pressure. The graph is divided into three parts. One part shows where water is a solid (ice). Another part shows where it is a liquid (water). And another part shows where it is a gas (steam). There is a special point on the graph called the triple point. At this temperature and pressure, water can exist as a solid, liquid, and gas at the same time. For water, this happens at 0.01 °C and a pressure of 611.657 pascals.

At normal air pressure (1 atmosphere), water freezes into ice at 0 °C (32 °F) and boils into steam at 100 °C (212 °F). The freezing point is the temperature at which water turns to ice. The boiling point is the temperature at which water turns into gas. Water does not need to be boiling to become gas. Even at low temperatures, some water molecules can move fast enough to evaporate. This is why a glass of water when left alone will slowly dry out. But when water is heated, the molecules move faster and evaporate quicker. When water reaches 100 °C, bubbles of water vapor form inside the liquid. These bubbles rise to the top and release steam into the air.

Water vapor (gas) can turn directly into ice without becoming liquid first. This is called deposition. You can see this when frost forms on cold windows. It also happens when snowflakes form in clouds. In clouds, tiny pieces of dust or pollen help water vapor turn straight into ice. The opposite of deposition is called sublimation. This is when ice turns straight into water vapor without becoming a liquid. One use of sublimation is in freeze-drying food. a method of preserving food. First, the food is frozen. Then it is put into a vacuum (a space with no air). The ice inside the food turns into vapor. This leaves the food dry, without using heat.

Water usually freezes at 0 °C (32 °F) at normal air pressure. But in special conditions, pure water can stay liquid even it is colder than that. If it is not shaken or disturbed, it can cool all the way down to about –42 °C (–44 °F) without freezing. This is called supercooling.

The melting and boiling points of water change with pressure. For most things, if you add more pressure, they melt at a higher temperature. But water is different because ice is less dense than liquid water. That is why ice floats. When pressure is added to ice, the melting point actually goes down. That means ice can melt even when it is colder than 0 °C if there is enough pressure. This can happen deep under a glacier. The heavy ice on top pushes down with a lot of pressure. This pressure can melt the ice under it, even though it is very cold. That is how lakes can form under glaciers.

Steam (which is water in gas form) takes up much more space than liquid water. That means it is less dense. When the pressure is high, it becomes harder for water to boil, so it needs to be hotter to turn into steam. In places with a lot of pressure, water can stay as a liquid even when it gets hotter than 100 °C (212 °F), which is the normal boiling point. For example, in geysers like Old Faithful, water can get over 205 °C (401 °F) without boiling. And near underwater volcanoes called hydrothermal vents, water can reach 400 °C (752 °F) and still stay liquid.

At sea level, water boils at 100 °C (212 °F). But when you go up higher like up the mountains, the air pressure gets lower. When pressure is lower, water boils at a lower temperature. For every 274 meters (or about 900 feet) you go up, the boiling point goes down by about 1 °C. For example, at 274 meters (about 900 feet), the boiling point becomes 99°C (210.2°F) instead of 100°C (212°F). That is why food takes longer to cook at higher altitudes. The water boils before it gets really hot. A pressure cooker works the opposite way. It traps steam inside, which raises the pressure. This lets water boil at a higher temperature, so food cooks faster. In places with no air at all, like in a vacuum, water can even boil at room temperature. This is because there is no pressure holding the water molecules together.

Taste and odor

People often say that water has no taste or smell. But in real life, most of the water we drink has some taste or smell. This is because there are usually tiny amounts of other substances dissolved in the water. Pure water does not have a taste, but our tongues can tell if something is mixed in. For example:

• Salts in water can give it a “mineral” taste, like water from springs.
• Water that is very acidic tastes sour.
• Water that is very basic (alkaline) tastes bitter.
• Tap water often has chlorine added to kill germs. This can give it a chemical or medicine-like taste.
• Metals like iron or copper can cause a metallic taste. This can be found in water from old pipes.

Even tiny amounts of these substances can change the taste. How strongly people taste them can depend on how cold or warm the water is and even a person's genes.

• Water can smell earthy or musty. This often come from natural chemicals like geosmin or 2-methylisoborneol (MIB) made by algae or bacteria in lakes and rivers.
• A rotten egg smell means the water might have hydrogen sulfide gas in it.
• Tap water might smell a little like chlorine, from the treatment process.

Some of these smells are so strong that the human nose can detect them even in very small amounts. Some animals, like frogs, can even smell water itself.

Mechanical properties

Water is often called incompressible. This means that even if you push on it really hard, it doesn’t shrink much. For example, at the bottom of the ocean, about 4 kilometers (2.5 miles) deep, the pressure is 400 times greater than at sea level. But water only gets about 1.8% smaller. This happens because water has a high bulk modulus (about 2.2 gigapascals). This means it resists being squeezed.

Viscosity is how easily a liquid flows. Water has low viscosity, so it flows quickly and easily, like in rivers or through pipes. Honey or syrup have high viscosity, so they flow slowly and are thick. Water flows smoothly through rivers, pipes, and the human body (like in blood vessels and cells). Viscosity changes with temperature. When a liquid gets warmer, it becomes thinner and flows more easily. When it gets colder, it becomes thicker and flows more slowly. So, warm water flows faster, and cold water flows slower. Water is called a Newtonian fluid. This means its viscosity stays the same even if you stir it fast or slow.

Sound travels through water at about 1,400 to 1,540 meters per second, depending on how warm, salty, or deep the water is. That is over 4 times faster than in air. Whales use sound to talk and find food underwater. Humans use tools like sonar to find things under the sea.

Electrical properties

Animation of the self-ionization of water

Water is a polar molecule. This means it has slightly charged ends. In water molecules, the hydrogen atoms have a small positive charge, and the oxygen atom has a small negative charge. This happens because oxygen pulls electrons closer to itself. That is because oxygen is more electronegative. It likes to attract electrons more than hydrogen does. This polarity helps water surround and pull apart other substances, especially those made of charged particles, like table salt (NaCl). When salt is added to water, the negative part of water (the oxygen) surrounds the positive sodium ions (Na⁺). The positive part (the hydrogen) surrounds the negative chloride ions (Cl⁻). This helps break the salt apart and keep the ions floating around in the water.

Water also has a high dielectric constant. It is about 80 at room temperature. That is much higher than most other liquids. This means water can reduce the electrical attraction between opposite charges. As a result, ions (like those from salt) can separate more easily in water. This is why it is so good at dissolving electrolytes. This makes it easier for ions to stay separate and move around freely. This is important for conducting electricity in biological and chemical systems. Thanks to its polarity and dielectric nature, water is one of the best solvents in the world. That is why it is called the "universal solvent".

Water can go through a special process called autoionization (also called self-ionization). This means that two water molecules can react with each other to make two new particles: a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻). One water molecule, takes a hydrogen from the other becoming a hydronium ion while the other is left with one hydrogen becoming a hydroxide ion.

The reaction looks like this:

H₂O + H₂O H₃O⁺ + OH⁻

This reaction does not happen often. At room temperature (25 °C), only a tiny number of water molecules do this. In pure water, the amounts of H₃O⁺ and OH⁻ are each 1 × 10⁻⁷ mol/L (moles per liter). That tiny amount makes water neutral and gives it a pH of 7. The pH scale, which tells us if something is acidic or basic, is based on this. Because there are so few ions, pure water does not conduct electricity well. That means pure water is more like an insulator than a conductor.

But water can dissolve ionic substances like salt very well. When you add even a little table salt (NaCl) to water, it releases lots of ions. The conductivity goes up a million times. That is why tap water and seawater conduct electricity so well. Seawater, for example, has ions like Na⁺, Cl⁻, and Mg²⁺, making it highly conductive. This matters in real life. Distilled water, which has no ions, can’t carry electricity. But regular water, with minerals or salts in it, can carry electric current. This is important in batteries, electrolysis, and even in cells in your body.

Optical properties

An indoor swimming pool appears cyan from above, as light reflecting from the bottom of the pool travels through enough water that its red component is absorbed. The same water in a smaller bucket looks only slightly cyan, and observing the water at close range makes it appear colorless to the naked eye.

In small amounts, water looks clear, but pure water actually has a slight blue tint. You can see the blue color more easily when you look at a large amount of water, like in a swimming pool, lake or ocean. The color comes from the way water interacts with light. Pure water absorbs some colors of light more than others. Those colors include the red, orange, and yellow parts of sunlight. This leaves more blue light to be reflected into our eyes. This is why water looks blue. You cannot see this in a glass of water. You can only see this when you are looking at deeper water, like in a swimming pool or lake. The deeper the water, the more light gets absorbed, and the more the blue color is seen. If water has something dissolved in it or tiny particles floating in it, the color can change. For example, algae and organic matter can make water look green or brown. Minerals and sediments in the water can change its color. Tannins from decaying plants can give water a tea-like, brownish color.

Visible light can mostly go through water. Blue and green light go the deepest in water. On the other hand, red, orange, and yellow light gets absorbed by the water, so they do not go very deep. In clear ocean water, sunlight can reach down to about 200 meters. This upper layer is called the photic zone. It is where there is enough light for plants and tiny algae like phytoplankton to do photosynthesis. Deeper than that, there is not enough light for plants to do photosynthesis.

Water bends light because it has a higher refractive index than air. The refractive index of water at room temperature (20°C or 68°F) is about 1.333. The refractive index of air is about 1.0. This means that when light enters water from the air, it slows down and bends. This is called refraction. It is this bending of light that causes a straw to look bent or broken in a glass of water. It is also why things under water look closer or larger than they actually are. Ice has a slightly lower refractive index (about 1.31). Because of this, light bends a bit less when passing through ice than through liquid water. The refractive index of water is similar to some liquids like ethanol and alkanes. But, it is lower than substances like glycerol, benzene, carbon disulfide, or glass (which range from 1.4 to 1.6). Also, the refractive index of water can change a little depending on the how how or cold it is, the pressure, or how much salt is in the water.

Chemical reactions of water

Water can react with some metals. It reacts with metals more reactive than hydrogen. When this happens, the metal reacts with water to make hydrogen gas and a metal hydroxide. Some metals, like the alkali metals (such as lithium, sodium, and potassium), react very strongly with water. Alkaline earth metals like calcium and magnesium react less violently. For example, sodium reacts violently and makes sodium hydroxide and hydrogen gas:

2Na + 2H
2O → 2NaOH + H
2

This reaction gives off a lot of heat (exothermic). It can even cause the hydrogen gas to catch fire.

Water is amphoteric. This means it can act like an acid or a base. This depends on what it is reacting with. When water is with a strong base, it gives away a hydrogen ion (H⁺) and acts like an acid. When water is with a strong acid, it takes in a hydrogen ion and acts like a base.

Water can also react with itself in a process called self-ionization:

H
2O + H
20 ⇌ H
3O+
+ OH−

This creates a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻). This reaction does not happen much in water. It helps set the pH scale, which tells us how acidic or basic a liquid is.

Water can also break one molecule into two smaller ones in a process called hydrolysis. The word comes from Greek: "hydro" meaning water, and "lysis" meaning to break or unbind. In hydrolysis, one molecule breaks into two molecules. A water molecule then breaks apart into a hydrogen ion and a hydroxide ion. The hydrogen ion attaches itself to one of the two new molecules. The hydroxide ion attaches itself to the other molecule. In industry, hydrolysis is used to break down compounds like esters or salts. In biology, proteins are broken into amino acids through hydrolysis. Fats (lipids) are broken into glycerol and fatty acids. Carbohydrates, such as sucrose, are broken into simpler sugars like glucose and fructose:

C
12H
22O
11 (sugar) + H
2O → C
6H
12O
6 (glucose) + C
6H
12O
6 (fructose)

Hydrolysis is the opposite of a condensation reaction. Condensation combines two molecules and releases water. Hydrolysis breaks one molecule into two smaller ones by adding water.

Water can be broken down into hydrogen gas (H₂) and oxygen gas (O₂), using a process called electrolysis. In this process, an electric current is passed through water that contains small amounts of an electrolyte like sulfuric acid or salt. This helps the water conduct electricity. The electricity breaks down the water molecules:

2H
2O → 2H
2 + O
2

Electrolysis is important because it produces clean hydrogen fuel when powered by renewable energy like solar or wind. This is often called green hydrogen. It can be used to store energy, power fuel cells, or replace fossil fuels in industry and transportation.

Water cycle

Water cycle

The water cycle (also called the hydrologic cycle) is the constant movement of water through the Earth's atmosphere and surface. Water moves between the air, ground, rivers, oceans, lakes, plants, and even underground. The main parts of the water cycle are:

• Evaporation: Water from oceans, lakes, and rivers changes into vapor (gas) and rises into the air.
• Transpiration: Plants release water vapor into the air through their leaves.
• Condensation: Water vapor in the air turns into clouds.
• Precipitation: Water vapor in the air cools, turns into liquid or solid, and falls back to Earth as rain, snow, or hail.
• Runoff: Water flows across the land into rivers, lakes, and oceans.

The sun is the main source of energy that drives the water cycle. When sunlight heats up water, the water molecules move faster and can turn into vapor. This a process called evaporation. This happens in oceans, lakes, rivers, and even from the land. Plants also release water vapor through their leaves in a process called transpiration. Together, evaporation and transpiration are called evapotranspiration. The term evapotranspiration is commonly used by geologists. Water vapor is invisible to our eyes.

Winds carry water vapor in the atmosphere over long distances. When water vapor cools down, it changes back into liquid water. This is called condensation. This can happen when warm air meets cool air. The water forms tiny drops around dust or salt called condensation nuclei in the air. These drops come together to form clouds. As more droplets stick together, they grow bigger. When they get heavy enough, they fall to Earth as rain, snow, or hail. This is called precipitation.

When precipitation reaches the ground, it can do the following. It can evaporate again. It can flow over the land as runoff into rivers and lakes. Or soak into the ground to become groundwater. Water that flows in rivers and lakes is called surface water. Water that moves underground through soil and rock is called groundwater. Groundwater moves slowly and can come back to the surface through springs. It can also flow into rivers, lakes, or oceans. This shows how surface water and groundwater are connected.

Most water that evaporates from the ocean goes back to the ocean. But wind blows water vapor to land at the same rate it goes back to the ocean. Each year, about 47 trillion tons of water vapor move from the ocean to the land. About 72 trillion more tons of water vapor comes from land evaporation and plants. That adds up to 119 trillion tons of precipitation falling on land each year. Precipitation over land has many forms. Most commonly rain, snow, and hail, with some being fog and dew. Dew are small drops of water that form when warm, wet air touches a cool surface, usually in the early morning. Water droplets in the air may also refract sunlight to produce rainbows.

Water that flows over land collects in places called watersheds. They then travel through rivers, carving out valleys and deltas. These areas usually have very good soil, which is good for farming and building cities. Sometimes, too much water causes a flood. This can happen when rivers overflow or big storms push water onto the land. Other times, there is not enough water. A drought happens when a place gets very little rain for a long time. This is often because of the place or shape of the land.

Water and Earth's geography

The Stone Forest near Kunming, China has hundreds of tall, sharp towers of limestone shaped by water

Water plays an important role in shaping the Earth’s surface and what is happening under it. It helps form landscapes. It breaks down rocks. It even affects volcanic activity from deep under the surface. Water changes the land through both physical actions, like erosion, and chemical reactions, like breaking down minerals in rocks.

Water plays a big role in breaking down rocks on Earth’s surface. This is a process called weathering. There are two main types: physical and chemical. In physical weathering, water gets into cracks in rocks. When it freezes, it expands and makes the cracks bigger. Over time, this causes the rock to break apart. In chemical weathering, water mixes with carbon dioxide from the air or soil. This creates a weak acid called carbonic acid. Carbonic acid can dissolve some types of rock, especially limestone. When this acid gets to limestone underground, it can create large cracks, caves, and tunnels. On the surface, it can create a type of landscape called karst. Here the ground has sinkholes, caves, and holes. One amazing example of karst is the Stone Forest near Kunming, China. It has hundreds of tall, sharp towers of limestone made by water. Another example is Carlsbad Caverns in New Mexico, USA. This park has over 119 caves, all formed by water breaking down limestone. The biggest one, called the Big Room, is so large it could fit six football fields inside.

Once rocks are broken down by weathering, the pieces are moved by a process called erosion. Water moves bits of rock and minerals away. No rock is strong enough to resist weathering and erosion forever. These powerful forces have created some of Earth’s most famous landmarks. For example, the Grand Canyon in Arizona, USA, was made by the Colorado River over millions of years. The canyon is about 446 kilometers (277 miles) long, up to 29 kilometers (18 miles) wide, and about 1.6 kilometers (1 mile) deep.

Water is also very good at moving sediment. Sediment is made up of small pieces of rock, sand, and soil. Rivers, glaciers, rain, and even ocean currents move sediment over long distances. Eventually, this sediment settles in new places. Sediment is important because it adds nutrients to the soil. This helps plants grow. Places with lots of sediment, like riverbanks and deltas, are usually great for farming. They have a lot of different plants and animals. For thousands of years, the Nile River in Egypt flooded every year. This brought about 4 million metric tons of nutrient-rich sediment. Even today, the land next to the Nile is Egypt’s best farmland. Over millions of years, layers of sediment can press together to form sedimentary rocks. These rocks can contain fossils and clues about Earth’s past, like what the climate was like long ago.

Deep inside the Earth, water plays an important role in forming magma. Magma is the hot, melted rock that can lead to volcanoes. The mantle is the thick layer under the Earth's crust. It is made of solid rock even though it is hot enough to melt rocks. This is because the pressure deep inside the Earth is so strong that it stops the rock from melting. But in places called subduction zones, one of Earth's tectonic plates goes under another plate. This brings water down into the mantle. This water lowers the melting point of the rock. This means the rock can start to melt even though it is still under very high pressures. This creates magma, which can rise and cause volcanic eruptions. So, water does not just shape the land on the surface, it also helps cause big changes deep underground. Over millions of years, water has helped shape how Earth looks and behaves.

In the Universe

Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.

Water is not only found on Earth. It can be found all over the universe. Astronomers have found ice, vapor, and sometimes liquid water in many places in the universe. Water ice has been found on the Moon, Mars, and comets. It has also been found on the icy moons of the outer planets, such as Europa and Enceladus. Even in interstellar space, the space between the stars, water exists as ice around tiny dust grains. It also exists as vapor in molecular clouds where new stars are born. Water has even been found in the atmospheres of exoplanets, planets outside our solar system.

A water molecule is made of two hydrogen atoms and one oxygen atom. Hydrogen came from the Big Bang. Oxygen was created inside big stars, much larger than the Sun. When these stars die and explode, they release oxygen into space. Oxygen can then combine with hydrogen to make water. Huge clouds of gas and dust, called stellar nurseries, are where new stars are born. These places often contain huge amounts of water vapor. For example, the Hubble Space Telescope found water molecules in the Helix Nebula. Water has also been found in young planetary systems around other stars. Around the star Beta Pictoris, which is about 20 million years old, scientists found water in a giant disk of gas and dust. This is likely from comets smashing into each other, asteroids, and forming planets. In the Orion Nebula, one of the biggest and most famous star-forming regions, water is still being made today. It is so large that it makes enough water every day to fill Earth’s oceans 60 times. All of this water, and the other molecules made in these star factories becomes part of new planets. On 22 July 2011, scientists found a gigantic cloud of water vapor that had 140 trillion times more water than the Earth's oceans combined around a quasar 12 billion light years from Earth. According to the researchers, the discovery shows that water has been in the universe for a very long time.

To find water in space, scientists make use of various tools and techniques. Telescopes with spectrometers can study the light coming from far away objects. Every molecule absorbs and emits light at specific wavelengths. By studying them, scientists can figure out whether there is water. Radio telescopes on the ground and space telescopes like the Hubble Space Telescope, the James Webb Space Telescope, and the Herschel Space Observatory have all helped us find water across the universe. In our own solar system, spacecraft missions have also been very important. NASA’s Galileo and Cassini missions found strong evidence of subsurface oceans on Jupiter's and Saturn’s moons. Cassini found geysers on Enceladus, with water vapor and ice particles erupting from the moon’s surface. On Mars, orbiters and rovers have found polar ice caps and certain rocks, which suggests that Mars might have had water in the past.

In the solar system

The gas released from the comet contains water vapor

Model of Europa's possible interior structure, with a thin ice crust and a subsurface ocean under it

South polar ice cap of Mars during Martian summer in the year 2000

Water can be found in many places in our Solar System. Earth is the only planet we know of that has liquid water on its surface all the time. Water can be found as: solid (ice), liquid (water), and gas (water vapor) on Earth. Scientists have found tiny amounts of water vapor in the Sun’s atmosphere. The Sun is very hot. Its surface is about 5,500°C (9,932°F) and the inside is even hotter. Normally, water breaks down into hydrogen and oxygen in such heat. But there are cooler spots on the Sun, like sunspots. At sunspots, temperatures can drop to about 3,000°C (5,432°F). That is still very hot, but cool enough for water molecules to form for a short time before they break apart into hydrogen and oxygen again.

The Moon and Mercury both have water ice hidden in craters near their poles. These craters are always in the dark and never get sunlight. Because of this, the ice has stayed frozen for billions of years. NASA spacecrafts, like the Lunar Reconnaissance Orbiter and MESSENGER, have found that these ice do exist. Venus has water vapor in its atmosphere, just like Earth. But its surface is very hot and harsh. This means it does not have any liquid water on its surface. Scientists think Venus may have had water in the past, but it was lost into space. This is because Venus does not have a magnetic field to protect it like Earth does. Mars has ice caps at its poles made of water and carbon dioxide. There is also ice under the ground in many places. Rovers and orbiters have also found hydrated minerals. This means that liquid water once flowed on the surface of Mars a long time ago.

Asteroids are found near a part of the solar system called the “frost line”. This is the distance from the Sun where it is cold enough for water to freeze into ice. Beyond this line, you usually won’t find liquid water because it is very cold. It can only be found hidden under ice, mixed with salt that keep it from freezing, or trapped under pressure in an atmosphere. One example is Ceres, a dwarf planet. It may have a layer of dust and rock on the outside, with salty water ice deep under the surface. Asteroids were once thought to be dry, but now scientists have found some that contain water ice or hydrated minerals. NASA’s OSIRIS-REx mission is helping us learn more about how much water some asteroids might have. Comets are pieces of ice leftover from the early solar system. They have a lot of frozen water. When a comet gets close to the Sun, the ice turns into gas, creating the famous glowing tails. There also exists a massive cloud of comets called the Oort cloud at the edge of the solar system.

The outer planets, Jupiter, Saturn, Uranus, and Neptune also have water. They are big gas giants or ice giants. They do not have a solid surface to walk on like our planet. Jupiter has water vapor in its thick atmosphere, but it is hard to see because of all the clouds. Saturn is like Jupiter. It has some water vapor in its atmosphere. Its beautiful rings are mostly made of water ice. Uranus might have an icy layer deep under its atmosphere. Neptune is similar to Uranus. Scientists think it also has an icy layer under its atmosphere that may contain water and other ices.

Some of the moons around the giant planets in our Solar System may have huge oceans of liquid water under their frozen surfaces. Europa, Ganymede, and Callisto, which orbit Jupiter, and Enceladus, and Titan, which orbit Saturn, might have underground oceans. Enceladus, a small moon of Saturn, shoots out jets of water vapor and ice from its south pole. A spacecraft named Cassini flew through these jets and found water, salts, and simple organic molecules. These are clues that there might be a hidden ocean with life. Titan, Saturn’s biggest moon, has lakes and seas on its surface, but they are filled with liquid methane and ethane, not water. Scientists think Titan has a salty water ocean deep underground, hidden under its icy surface. The moons of Uranus also have icy surfaces. Titania, the largest, has water ice and carbon dioxide ice. There might be liquid water under its surface. Triton, Neptune’s biggest moon, has a surface of frozen water ice. Deep under that ice, scientists also think it might have a liquid ocean.

The dwarf planet Pluto has a surface covered in frozen nitrogen and water ice. Pluto is extremely cold and far from the Sun. Scientists think Pluto might have a liquid ocean deep beneath its icy crust, about 100 kilometers deep. Pluto’s biggest moon, Charon, also has water ice. Beneath the surface, Charon may have had liquid water in the past. Some scientists think ice geysers might still happen on Charon.

In interstellar space

The Orion Nebula, a molecular cloud where stars are born, contains a huge amount of water mostly in the form of ice

Water is not only found on planets and moons. It can also be found in the vast spaces between stars, the interstellar medium. The interstellar medium (ISM), is the scattered mix of gas, dust and radiation that can be found in the space between the stars in a galaxy. Water can be mainly found as ice covering dust grains in the interstellar medium and dense molecular clouds, where new stars are born. It can also be found as water vapor inside dense molecular clouds. In the coldest parts of the ISM, water molecules condense onto the surfaces of dust grains, forming icy mantles. These icy grains are very important ingredients in the chemistry of making stars and planets.

Molecular clouds, places where stars and planets are born, contain huge amounts of water. Water vapor has been found in many of these clouds, especially near newly forming stars. As young stars fuse hydrogen into helium they release heat around them. This warms up the surrounding ices, turning them into water vapor. This allows them to be observed by space telescopes such as the Herschel Space Observatory and the Spitzer Space Telescope. One of the most famous places where water has been studied is the Orion Nebula. Here, astronomers have found huge amounts of water vapor surrounding stars being born. In these environments, water is also very important in the chemistry that creates more complex organic molecules like amino acids. The Rho Ophiuchi cloud complex is a nearby molecular cloud about 460 light-years away. It contains protostars surrounded by water-rich ices. The ice in this region has been found using telescopes like Spitzer and JWST.

Ice and tiny grains of dust were the main ingredients that came together to form the Solar System. Scientists believe that the water in the solar system formed in space before our Sun or planets even existed. When star systems begin to form, gravity pulls together this gas and dust to make stars and planets. The dust already has water on it, which can become part of the new planets. That means planets like Earth might have been born with water already inside them.

On exoplanets

Artist's impression of K2-18b (right) orbiting red dwarf K2-18 (left). The exoplanet K2-18c is shown between them. How the planet actually looks like is unknown.

When looking for life on other planets, called exoplanets, water is one of the most important molecules scientists look for on other planets. We cannot use a telescope to look into other planets for water because they are very far away. But, astronomers have found others ways to look for water on some of these far away planets. The main way scientists study planets outside our Solar System is through something called transit spectroscopy. This means watching a planet as it passes in front of its star. When it does, some of the star’s light goes through the planet’s atmosphere to us. Depending on what the atmosphere is made of, certain parts of the light get blocked or bent. This creates a kind of “fingerprint” in the light that scientists can study. By looking closely, they can figure out which gases are in the atmosphere, like water or methane. Right now, studying the atmospheres of exoplanets is still very hard. Our tools are not perfect for this yet and it takes very careful measurements.

This method has found water vapor on many "hot Jupiters", such as HD 189733 b and HD 209458 b. These are large gas giants very close to their stars. Though these planets are far too hot for liquid water. Water exists as water vapor in the atmospheres of these planets. In recent years, telescopes have begun finding signs of water on smaller planets, especially sub-Neptunes and super-Earths. These are planets smaller than gas giants but larger than the Earth. One example is K2-18b, a super-Earth found by NASA's Kepler spacecraft in 2015. It is a planet with eight times the mass of the Earth that orbits a so called red dwarf star, which is much cooler than the sun. K2-18b can be found in the “habitable zone” of its star. This means it has the right temperature to have liquid water. Given its mass and radius, K2-18 b is not a gaseous planet. It is most likely a terrestrial planet with rocky surface. Observations with Hubble and the James Webb Space Telescope (JWST) have found water vapor in its atmosphere. Though scientists cannot say if it has clouds, oceans, or even rain.

The search for liquid surface water on rocky exoplanets is still going on and much harder. Scientists rely on indirect signs like planet size, density, temperature, and how close it is to its star to figure out whether a planet might have oceans. Planets in the so-called "habitable zone", where temperatures could allow water to remain liquid, are very good places to look with new technology like the James Webb Space Telescope.

Uses of water

Plants and animals (including people) are mostly water inside, and must drink water to live. It gives a medium for chemical reactions to take place, and is the main part of blood. It keeps the body temperature the same by sweating from the skin. Water helps blood carry nutrients from the stomach to all parts of the body to keep the body alive. Water also helps the blood carry oxygen from the lungs to the body. Saliva, which helps animals and people digest food, is mostly water. Water helps make urine. Urine helps remove bad chemicals from the body. The human body is between 60% and 70% water, but this value differs with age; i.e. a foetus is 95% water inside.

Water is the main component of drinks like milk, juice, and wine. Each type of drink also has other things that add flavor or nutrients, things like sugar, fruit, and sometimes alcohol. Water that a person can drink is called "potable water" (or "drinking water"). The water in oceans is salt water, but lakes and rivers usually have unsalted water. Only about 3% of all the water on earth is fresh water. The rest is salt water.

Drop of water falling from a faucet.

Many places, including cities and deserts, don't have as much water as people want. They build aqueducts to bring water there.

Though people can survive a few months without food, they can only survive for a day or two without water. A few desert animals can get enough water from their food, but the others must drink. Water has no smell, taste, or color.

Water is also used for recreational purposes, see list of water sports.

Water is used as both the coolant and the neutron moderator in most nuclear reactors. This may be ordinary water (called light water in the nuclear industry) or heavy water.

Water is also used for washing a lot of objects. Goods, services and people are transported to other countries in watercrafts on bodies of water.

Water is used in chemical reactions as a solvent or reactant. Water is also used in fire fighting. Water is also used for cooking.

Dihydrogen monoxide parody

The dihydrogen monoxide parody involves calling water by the unfamiliar chemical name "dihydrogen monoxide" (DHMO) and listing some of its harmful effects in an alarming way. Some examples include talking about how "it causes burning, suffocation and corrosion," when it is actually just talking about hot water, drowning and rust. Sometimes the parody calls for it to be banned and/or labelled as dangerous.

The prank works because it takes advantage of people's misunderstanding. Calling water by an unfamiliar name and making it sound like a harmful chemical can make people think it is dangerous.

"Dihydrogen monoxide" is an alternative chemical name for water, but nobody uses it. The word "dihydrogen" means two hydrogens, and "monoxide" means one oxygen. The chemical formula of water has two hydrogen atoms and one oxygen atom.

The parody gained most of its popularity in the 1990s, when a 14-year-old named Nathan Zohner collected anti-DHMO petitions for a science project about gullibility. Zohner fooled a lot of people, which has led to his project being used in lessons about critical thinking and the scientific method.

The website DHMO.org is a joke website which lists the harmful effects of water (DHMO), answers questions, and calls for it to be banned, among other things.

Water Media

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  Specific heat capacity of water

• 

  Overview of photosynthesis (green) and respiration (red)

• 

  Photo of a fountain in the Italian Garden section of en:Longwood Gardens in Kennett Square, en:Pennsylvania. Photo taken by Michael Parker. Original: Fountain

• Water distribution in subsurface drip irrigation

Related pages

• Ice
• Lake
• Life timeline
• Nature timeline
• Pond
• Rain
• River
• Sea
• Steam
• Water cycle
• Waterway
• Water vapor

Other websites

• Water Citizendium
• Importance of Water Archived 2021-09-28 at the Wayback Machine