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Most water in Earth's atmosphere and crust comes from saline seawater, while fresh water accounts for nearly 1% of the total. The vast bulk of the water on Earth is saline or salt water, with an average salinity of 35‰ (or 3.5%, roughly equivalent to 34 grams of salts in 1 kg of seawater), though this varies slightly according to the amount of runoff received from surrounding land.
Water is a basic necessity of life. Since two thirds of the Earth is covered by water, the Earth is also called the blue planet and the watery planet. [notes 1] The hydrosphere plays an important role in the existence of the atmosphere in its present form. Oceans are important in this regard.
Hydrology (from Ancient Greek ὕδωρ (húdōr) 'water' and -λογία 'study of') is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydrologist.
Antarctica provides the water hemisphere with the majority of Earth's ice. Most of the Pacific Ocean and the Indian Ocean, and the whole Southern Ocean, are in the water hemisphere. The water hemisphere is approximately 89 percent water (almost all pertaining to the World Ocean), 6 percent dry land and 5 percent polar ice cap. [1]
The deuterium to hydrogen ratio for ocean water on Earth is known very precisely to be (1.5576 ± 0.0005) × 10 −4. [35] This value represents a mixture of all of the sources that contributed to Earth's reservoirs, and is used to identify the source or sources of Earth's water.
Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles). [24] Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is seawater. Water is also present in the atmosphere in solid ...
Hydrometeorology – the study of the transfer of water and energy between land and water body surfaces and the lower atmosphere Isotope hydrology – the study of the isotopic signatures of water Surface hydrology – the study of hydrologic processes that operate at or near the Earth 's surface
Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. These resources can be either freshwater from natural sources, or water produced artificially from other sources, such as from reclaimed water or desalinated water (). 97% of the water on Earth is salt water and only three percent is fresh ...