مستخدم:سبا8\5/ملعب
water[عدل]
Water is a transparent, colorless and odorless substance. It is the main constituent of streams, lakes, seas and oceans, as well as the fluids of all living organisms. It is the most prevalent chemical compound on the Earth's surface. A water molecule consists of a central oxygen atom to which two hydrogen atoms are covalently bonded on both ends, so that its chemical formula is H2O. At standard conditions of pressure and temperature, water is a liquid; As for the solid state, it forms at the freezing point, and it is called ice; As for the gaseous state, it forms at the boiling point, and it is called water vapor
Water is the basis for the existence of life on the planet, and it covers 71% of its surface, and sea and ocean waters represent the largest percentage of water on Earth, reaching about 96.5%. The remaining percentages are distributed between groundwater and polar ice (1.7% for both), with a small percentage in the form of water vapor suspended in the air in the form of clouds (clouds), and sometimes in the form of fog or dew, in addition to rain or snow showers. Fresh water is only about 2.5% of the water on Earth, and most of this amount (about 99%) is found in glaciers in the polar regions, while 0.3% of fresh water is found in rivers, lakes and the atmosphere.
In nature, the state of water changes between the three states of matter on the surface of the earth constantly through what is known as the water cycle (or the water cycle), which includes the occurrence of evaporation and transpiration (evaporative transpiration), then condensation, precipitation, and then runoff to reach the mouth of water bodies.
Access to a clean source of drinking water was important for the emergence of civilizations throughout history. In recent decades, fresh water shortages have been recorded in many regions of the world, and United Nations statistics have estimated that about one billion people on Earth still lack the available means to access a safe source of drinking water, and that about 2.5 billion lack an adequate means to Water disinfection.
