How Much Water Is on Earth?

­The oceans are huge. They cover about 70 percent of the planet, and the average depth of the ocean is about 12,100 feet (3,688 meters). About ninety-seven percent of the water on the planet is in the oceans, and therefore, is unusable as drinking water because of the salt.

The Pacific Ocean is the largest ocean by a significant margin. The basin can hold all of the continents. Following the Pacific Ocean is the Atlantic Ocean, then the Indian Ocean, the Southern Ocean and the Arctic Ocean.

Less than 3 percent of Earth's water is fresh, but about 1.6 percent of the planet's water is not in liquid form, locked in the polar ice caps and glaciers. Another 0.36 percent is underground in aquifers and wells.

Only about 0.036 percent of the planet's total water supply is surface water, found in freshwater lakes and rivers. That's still thousands of trillions of gallons, but it's a very small amount compared to all the water available.

Now That's a Lot o' Lakes

At last count, there were 117 million lakes in the world, covering nearly 4 percent of the world’s land surface, (excluding the glaciers of Greenland and Antarctica). There are 1,681 lakes in the United States, but Lake Baikal in Russia is the largest freshwater lake by both volume and depth.

The rest of the water on the planet is either floating in the air as clouds and water vapor, or inside plants and animals, or hiding as soil moisture. Your body is 65 percent water, so if you weigh 100 pounds, 65 pounds of you is water.

With all the soda pop, milk and orange juice you see at the store and in your refrigerator, there are probably several billion gallons of water sitting on a shelf at any one time!

In the United States, drinking water primarily comes from two main sources: surface water and groundwater. Sources of surface water include reservoirs, lakes and rivers. Groundwater, found beneath the Earth's surface in aquifers, also serves as a significant source of drinking water, especially in rural and less populated regions.

Both sources undergo rigorous treatment processes to ensure the water is safe and meets the stringent quality standards set by the Environmental Protection Agency (EPA) before it reaches homes and businesses for consumption.

The water cycle, also known as the hydrologic cycle, is a continuous and dynamic process that describes the movement of water on, above and below the Earth's surface. It plays a pivotal role in distributing and renewing Earth's water resources.

The cycle begins with evaporation, which is when the Sun's heat causes water from surface sources like oceans, rivers and lakes to transform into water vapor, rising into the atmosphere. This then condenses to form clouds. After that comes precipitation, where water droplets in clouds combine and fall as rain, snow, sleet or hail.

Some of this water returns to bodies of water through runoff, while another part of it ends up absorbed into the ground. Evaporation of the runoff begins the cycle anew.

The Effects of Climate Change

Climate change impacts the water cycle, altering its dynamics. Climate change causes shifts in sea levels and precipitation patterns, leading to more intense rainfall events in some regions and prolonged droughts in others.

Climate change can also influence water quality, affecting the concentration of pollutants and contaminants in bodies of water.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.