From the ancient Greek hydro "water" + sphere "ball".

The discontinuous water envelope of the globe, representing the totality of all water bodies of the Earth - oceans, seas, lakes, rivers, reservoirs, ponds, swamps, streams, as well as water accumulations in the form of glaciers and snow cover.

The hydrosphere is commonly divided into the world's oceans, continental surface waters and glaciers, and underground waters. The volume of the hydrosphere is 1370.3 million km3 , which is about 1/800 of the volume of the planet. 98.3% of the mass is concentrated in the world's oceans and 1.6% in the land ice. 

Most of the water is concentrated in the ocean, with much less in glaciers, continental reservoirs and groundwater. Salt ocean water makes up 96.4% of the hydrosphere; glacier water accounts for 1.86%; groundwater, 1.68%; and surface land water, just over 0.02%. The volume of fresh water is 2.5% -35 mln km³, extractable 0.3% -4.2 mln km³. 

The oceans cover about 71% of the Earth's surface. Their average depth is 3800 m, and their maximum depth (the Mariana Trench in the Pacific Ocean) is 10,994 m. The oceanic crust is composed of sedimentary and basaltic layers. 

The waters of the World Ocean contain dissolved salts (3.5% on average) and a number of gases. In particular, the upper layer of the ocean contains 140 trillion tons of carbon dioxide and 8 trillion tons of oxygen.

Surface continental waters occupy only a small proportion of the total mass of the hydrosphere, but nevertheless play a crucial role in the life of the terrestrial biosphere, being the main source of water supply, irrigation and watering. In addition, this part of the hydrosphere is in constant interaction with the atmosphere and the Earth's crust. 

Water that is in a solid state (in the form of glaciers, snow cover and permafrost) is united under the name of the cryosphere.

The transition of water from one part of the hydrosphere to another constitutes the complex water cycle on Earth. The hydrosphere overlaps with the biosphere throughout its entire thickness, but the greatest density of living matter occurs in the surface layers warmed and illuminated by the Sun, as well as the coastal zones. The hydrosphere is thought to be where life on Earth originated. It was only at the beginning of the Paleozoic Era that animals and plants gradually emerged on land.