What is Water?

What exactly is water?

Water is two atoms of hydrogen (H) and one atom of oxygen (O) which join together with a covalent bond to form one water molecule (H₂O). Once these atoms are joined with covalent bonds, they are difficult to separate. This is why water molecules remain so stable throughout Earth's environment!

In fact...

Water is the only common substance on Earth that occurs in all three states of matter: liquid, solid (ice), and gas (water vapor)!

This is because Earth is at the perfect distance from the Sun to place it within a temperate zone different from all other planets in our solar system. This temperate location allows all three states of water - liquid, solid, and gaseous - to co-exist on Earth!

This picture shows water in all its material states: liquid (ocean water), solid (frozen as sea ice), and gaseous (water vapor in clouds).

Water as a resource

Water is a renewable resource, meaning it will replenish through natural processes on a human time scale. In the case of water, it is constantly cycling through the environment via the hydrologic cycle (discussed in more detail on the next page).

However, even though water is considered a renewable resource, access to safe drinking water is deeply uneven. Consider some of the following statistics:

• An estimated 2.2 billion people - or one in three people globally Links to an external site. - lack access to safe drinking water. However, some researchers estimate that this number is closer to 4.4 billion people in low- and middle-income countries Links to an external site. - or half the world's population.
• 1.5-2 billion people lack access to basic sanitary facilities such as a toilet or latrine.
• Unsafe water sources are responsible for over 1 million deaths per year. Links to an external site.

Salt Water

The vast majority of Earth's water is contained in its oceans - in fact, about 96.5% of all water is in Earth's oceans! Approximately 48% of that water (by surface area, not volume) is in the Pacific ocean. This water is not available for human consumption due to its salt content.

Fresh Water

Only ~2.5% of Earth's water is fresh (non-saline) water.

• Roughly 1.7 to 2.1% is contained in the cryosphere (polar ice caps, glaciers, permafrost, etc.)
• ~0.75% is in groundwater
• ~0.007% is in surface water (e.g. lakes, rivers, swamps, marshes)
• Only ~0.0009% of Earth's water is located in the atmosphere as water vapor

The majority (between 65-75%) of Earth's fresh water is stored in glaciers, making glaciers the largest reservoir of freshwater on Earth!