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Water and Life

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Dihydrogen oxide or dihydrogen monoxide. Does this chemical sound dangerous?

Another name for this compound is…water. Water can create some absolutely beautiful sights. Iguassu Falls is the largest series of waterfalls on the planet, located in Brazil, Argentina, and Paraguay. And water is necessary for life. The importance of water to life cannot be emphasized enough. All life needs water. Life started in water. Essentially, without this simple three atom molecule, life would not exist.



Water, Water Everywhere


Percentage of fresh water on Earth

Most of the water on Earth consists of saltwater in the oceans. What percent of Earth’s water is fresh water? Where is most of the fresh water found?

Structure and Properties of Water

No doubt, you are already aware of some of the properties of water. For example, you probably know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food.

Chemical Structure of Water


Structure of water molecule and solvation


Opposites attract when it comes to charged molecules. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules, as shown in Figure below . The type of bond that forms between molecules is called a hydrogen bond . Bonds between molecules are not as strong as bonds within molecules. There are just many more hydrogen bonds in water (between water molecules) than there are covalent bonds within a molecule. The hydrogen bonds may not be strong, but in water they are strong enough to hold together nearby molecules.

Hydrogen Bonding in Water Molecule

Hydrogen Bonding in Water Molecules. Hydrogen bonds form between nearby water molecules. How do you think this might affect water’s properties?

Properties of Water

Hydrogen bonds between water molecules explain some of water’s properties. For example, hydrogen bonds explain why water molecules tend to stick together. Have you ever watched water drip from a leaky faucet or from a melting icicle? If you have, then you know that water always falls in drops rather than as separate molecules. The dew drops in Figure below are another example of water molecules sticking together.

Droplets of dew clinging to a spider web

Droplets of Dew. Drops of dew cling to a spider web in this picture. Can you think of other examples of water forming drops? (Hint: What happens when rain falls on a newly waxed car?)

Hydrogen bonds cause water to have a relatively high boiling point of 100°C (212°F). Because of its high boiling point, most water on Earth is in a liquid state rather than in a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (mass/volume) than liquid water. The lower density of ice means that it floats on water. For example, in cold climates, ice floats on top of the water in lakes. This allows lake animals such as fish to survive the winter by staying in the water under the ice.

Water and Life








  • Water is needed by all known forms of life.
  • Due to the difference in the distribution of charge, water is a polar molecule.
  • Hydrogen bonds hold adjacent water molecules together.
  • Water is involved in many biochemical reactions. As a result, just about all life processes depend on water.

Explore More

Use these resources to answer the questions that follow.

Explore More I

  1. How do hydrogen and oxygen bind to form water?
  2. Why is water a polar molecule?
  3. Describe the bond between water molecules.

Explore More II

  1. Describe two properties of water that make it important to life.
  2. Why is the specific heat of water important?
  3. Why does ice float?


  1. Where is most of Earth’s water found?
  2. What percent of Earth’s water is fresh water?
  3. What is polarity? Describe the polarity of water.
  4. How could you demonstrate to a child that solid water is less dense than liquid water?
  5. Explain how water’s polarity is related to its boiling point.
  6. Explain why metabolism in organisms depends on water.

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