Our planet is often called the “Blue Planet” because water covers approximately 71 percent of its surface. This substance is fundamental for all known life forms, playing a role in cellular processes and shaping Earth’s landscapes. Water exists in various forms and resides in many locations across the globe.
Oceans as the Primary Reservoir
The vast majority of Earth’s water, around 96.5 to 97 percent, is held within the oceans. This volume, estimated at 321 million cubic miles, primarily consists of saltwater. The high concentration of dissolved salts, mainly sodium chloride, renders it unsuitable for direct human consumption or agricultural irrigation without extensive and costly desalination.
The Planet’s Freshwater Stores
While oceans dominate the total water supply, the planet’s freshwater, suitable for most human uses, represents a much smaller fraction, approximately 3.5 percent of all water. This limited resource is distributed across several significant reservoirs.
Over two-thirds of all freshwater, about 68.7 to 69 percent, is locked away in ice caps and glaciers. These frozen bodies are predominantly found in the polar regions, with the Antarctic and Greenland ice sheets containing over 99 percent of Earth’s surface ice. These ice formations represent the largest freshwater reserve on the planet.
Beneath the Earth’s surface lies the largest store of liquid freshwater, known as groundwater, accounting for roughly 30 to 30.1 percent of the total freshwater. This water saturates porous rock formations and sediment layers called aquifers. Groundwater serves as a significant source for drinking water and irrigation worldwide, accessed through wells and natural springs.
Surface water bodies, including lakes, rivers, and wetlands, hold the smallest visible portion of freshwater, less than one percent of the total freshwater supply. Lakes contain about 87 percent of this surface freshwater. Rivers, though comparatively small in volume, are a readily accessible and widely utilized source for human needs. Wetlands, such as swamps, also contribute to this surface water category.
Atmospheric and Biological Water
Beyond the major reservoirs, smaller but significant amounts of water exist in the atmosphere and within living organisms. Atmospheric water, present as vapor, clouds, and humidity, represents a minute fraction of Earth’s total water, approximately 0.001 percent. This atmospheric moisture plays a role in weather patterns and the global water cycle, facilitating water redistribution.
Water is also an intrinsic component of all biological life on Earth. Every living organism, from microscopic bacteria to vast forests, contains water within its cells and tissues. This biological water, while not a separate reservoir like oceans or glaciers, collectively represents a part of the planet’s water distribution.