The planet Earth is blue, the colour of our sky and the sea reflected in it. Over 3/4 of the planet is covered by oceans, and within the continents there are huge masses of water in fresh and salt water lakes. But the water is not always visible.
The Earth's oceans hold 96.5% of the water on Earth. 1,338 billion Km3 of water. But not a single drop of fresh water!
Glaciers and ice sheets on Earth are the largest reserve of fresh water on the planet, more than 24 million km3, 68.6% of the total ice mass, though this is only 1.74% of Earth's water.
Groundwater, stored in rocks and sediments, is the second largest fresh water reserve of the planet, almost as large as the water frozen in the ice caps and glaciers: 23.4 million km3 of water are hidden in the earth's lithosphere, though only 45 % of this is fresh water, whereas the other 55% is more or less salty water. Still, groundwater accounts for 30% of global freshwater reserves.
The lakes and wetlands of the interior of continents hold only 0.014% of the total water on Earth, and nearly half their volume is salt water, so that the volume of all freshwater lakes on Earth is around 102,000 km3, 0.29% of terrestrial reserves.
Despite its shallowness, edaphic-soil which nourishes and gives drink to terrestrial plants – holds 0.05% of Earth's fresh water: 16,500 km3, which is essential for life on the continents.
The atmosphere contains the equivalent of 12,900 km3 of liquid water. Although this is only 0.04% of the planet's fresh water, the water in the atmosphere is quickly renewed – every 9-10 days on average – thereby discharging enough water as rain or snow to maintain the hydrological cycle.
Earth's rivers contain 2,120 km3 of fresh water: 0.006% of total freshwater.
Living beings have in their bodies one millionth of the Earth's total water or, which is the same, half of the water flowing through the rivers.
The permafrost or frozen ground is an important reservoir of fresh water as, though they are found only in polar areas and high mountains, these frozen soils can be hundreds of metres in depth and accrue an estimated volume of 300,000 km3 of fresh water, 0.86% of the total reserves, more than all the Earth's lakes, rivers and clouds