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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.
Only 3% of the world's population lived in urban areas in 1800; this proportion had risen to 47% by 2000, and reached 56% by 2020. [ 38 ] The world's population is over 8 billion [ 39 ] and Earth 's total surface area (including land and water) is 510 million square kilometres (197 million square miles). [ 40 ]
Population density (people per km 2) by country. This is a list of countries and dependencies ranked by population density, sorted by inhabitants per square kilometre or square mile. The list includes sovereign states and self-governing dependent territories based upon the ISO standard ISO 3166-1.
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 ...
Water can be polluted, abused, and misused but it is neither created nor destroyed, it only migrates. There is no evidence that water vapor escapes into space." [12]: 26 Every year the turnover of water on Earth involves 577,000 km 3 of water. This is water that evaporates from the oceanic surface (502,800 km 3) and from land (74,200 km 3).
Scientists analyzed water samples flowing through eight large publicly owned wastewater plants across the US, all of similar size and using similar technologies to those serving 70% of the population.
Most of Earth's surface is ocean water: 70.8% or 361 million km 2 (139 million sq mi). [96] This vast pool of salty water is often called the world ocean, [97] [98] and makes Earth with its dynamic hydrosphere a water world [99] [100] or ocean world. [101] [102] Indeed, in Earth's early history the ocean may have covered Earth completely. [103]
In the future, even more water will be needed to produce food because the Earth's population is forecast to rise to 9 billion by 2050. [63] In 2000, the world population was 6.2 billion. The UN estimates that by 2050 there will be an additional 3.5 billion people, with most of the growth in developing countries that already suffer water stress ...