Because we live on land, it’s easy to forget that the Earth’s surface is mostly covered in water. In fact, about 71 percent of the total surface of the globe is underwater.
The world’s oceans hold about 96.5 percent of all of the Earth’s water, all of which is saline, or salt water. Freshwater lakes, streams, rivers and groundwater are the primary water source for people to drink, making it critical for the support of life.
Then there is water in the vast glaciers and ice caps on the Earth’s poles, as well as water vapor in the air and aquifers beneath the ground.
Scuba Dive in Hawaii — Water Is Constantly on the Move
Water is constantly moving. The water cycle evaporates water from the seas and lifts this moisture into the air, before dropping it back down again in the form of rain or snow.
This rainfall is what fills up rivers and lakes, providing freshwater that supports all forms of life. But some of this water also seeps into the ground, feeding the underwater aquifers beneath our feet.
In reality, there is more freshwater stored in the ground than there is in liquid form on the planet’s surface. In fact, much of the water you see flowing past in rivers is actually formed by seepage of groundwater into the riverbeds rather than from rainfall.
Rain will recharge underground aquifers while water in the ground recharges the rivers that feed into the seas, to create one big planetary water ecosystem.
Scuba Dive Hawaii — Daily Water Use
Humans use both river water and the aquifer. In the US alone, about 275 billion gallons of surface water are used per day, as well as about 79.3 billion gallons of groundwater.
Surface water is more likely to supply drinking water and for irrigation of crops. Groundwater helps keep rivers and lake levels constant, as well as providing a water source for places where visible water is scarce, such as in desert towns.