Water is an essential compound for all known life forms to date on Earth, but not on other planets. Its chemical formula is H2O, in which each molecule contains one oxygen and two hydrogen atoms linked by covalent bonds. Water covers almost 71% of the Earth's surface. There are 1.4 trillion cubic kilometers (330 million mi³) of water available on Earth. Water is mostly found in the ocean (salt water) and in ice sheets (at the poles and mountain peaks). In addition, water can also be found in clouds, rain, rivers, surface fresh water, lakes, water vapor, and sea ice. The water in these objects moves following a water cycle, namely: through evaporation, rain, and the flow of water over the land surface (runoff, including springs, rivers, estuaries) to the sea. Clean water is important for human life.
Apart from Earth, large amounts of water are also thought to be present at the north and south poles of the planet Mars, as well as on the moons Europa and Enceladus. Water can be in the form of solid (ice), liquid (water) and gas (water vapor). Water is the only substance that naturally exists on the surface of the Earth in all three of its forms. Poor management of water resources can lead to water shortages, monopolization and privatization and even spark conflict. Indonesia has had a law that regulates water resources since 2004, namely Law No. 7 of 2004 concerning Water Resources. However, because the law was deemed to be contrary to the 1945 Constitution, the Constitutional Court annulled all the articles contained in the law. Thus, Law Number 11 of 1974 concerning Irrigation was again applied to fill the legal vacuum until the formation of a new law.
Chemical and physical properties
Water is a chemical substance with the chemical formula one water molecule is composed of two hydrogen atoms covalently bonded to one oxygen atom. Water is colorless, tasteless and odorless under standard conditions, namely at a pressure of 100 kPa (1 bar) and a temperature of 273.15 K (0 °C). This chemical is an important solvent, which has the ability to dissolve many other chemicals, such as salts, sugars, acids, certain gases and many kinds of organic molecules.
The liquid state of water is unusual under normal conditions, especially considering the relationship between other similar hydrides in the oxygen column of the periodic table, which suggests that water should be a gas, as hydrogen sulfide. By looking at the periodic table, it can be seen that the elements surrounding oxygen are nitrogen, fluorine, and phosphorus, sulfur and chlorine. All of these elements when combined with hydrogen will produce gases at normal temperatures and pressures. The reason why hydrogen bonds with oxygen to form a liquid state is because oxygen is more electronegative than the other elements (except fluorine).
The oxygen atom's attraction to the bonding electrons is much stronger than that of the hydrogen atom, leaving a net positive charge on both hydrogen atoms, and a total negative charge on the oxygen atom. The presence of a charge on each of these atoms makes the water molecule have a number of dipole moments. The electric attraction between water molecules due to the presence of this dipole brings each molecule close to each other, making it difficult to separate and ultimately increasing the boiling point of water. This attraction is known as hydrogen bonding.
Water is often referred to as the universal solvent because it dissolves many chemicals. Water is in dynamic equilibrium between the liquid and solid phases under standard pressure and temperature. In its ionic form, water can be described as a hydrogen ion (H+) associated with a hydroxide ion (OH-).
Here are the physical constants of water at a certain temperature: