Water is an extremely abundant chemical compound that is necessary for all life on Earth that has the chemical formula H2O/HOH. At room temperature, it is a highly viscous, tasteless, orderless and almost colorless liquid with a blue tinge. When it is a solid, it is called ice and it is known as vapor when it has reached the gaseous phase. It covers almost 75% of the Earth's surface in the form of oceans, seas and lakes. It is present in the atmosphere in the form of clouds and it exists in its solid form in the ice caps. Because it can dissolve just about anything (hence the term, universal solvent), water is almost never found pure in nature.
Water is a polar molecule; meaning that there is a great difference between the electronegativites of its atoms. In this case, the electrons in the covalent bond are more attracted towards the highly electronegative oxygen (electronegativity: 3.46) rather than the hydrogen atom (electronegativity: 2.20), giving it a negatively charged pole and a positively charged pole. This polarity allows water to easily interact with and dissolve most other polar substances such as sugars, alcohols and salts. Certain materials, such as oils, fats and steroids, mix poorly with water because they're non-polar.
The atraction ability of hydrogen to have an attraction to a neighboring molecule is known as a hydrogen bond and it allows for water molecules to be closer together when compared to other fluids (this hydrogen bond is also the reason as to why water tends to have a higher boiling point when compared to other molecules of similar size). Water's ability to atract itself towards another amount of water is known as cohesion, while its ability to become attracted to another substance is known as adhesion.
In addition, water has an extremely high surface tension; meaning that any sample of water it has a surface that strongly resists being stretched due to its cohesion (this is what allows certain insects to literally walk on the liquid). Furthermore, the high specific heat capacity of water is what allows this compound to act as a major influence on the movement of heat throughout the Earth. Having a high specific heat means that water can absorb much heat before it actually gets hot and it also exlpains as to why temperature change is rather gradual between seasons instead of being sudden.
It is considered an amphoteric substance because it can either accept a proton or donate it depending on the chemical reaction. It has a natural pH of seven, so it cannot be considered basic or acidic.
Water also has two isotopologues (almost identical molecules that only differ in their isotopic composition); heavy water (deuterium oxide) and super heavy water (tritium oxide). The first is almost identical to water, but it serves no biological role and should not replace water completely (however, poisoning due to excessive heavy water levels is unlikely since it'd take a considerable amount of deuterium oxide to replace most of the water in the human body). Deuterium oxide has been used in nuclear reactors as a neutron moderator. The latter of the two isotopologues, super heavy water, is corrosive because of radiolysis (the tritium atom is radioactive and has a half-life of 12.38 years) and it can be used to date vintage wines.
Water helps to deliver nutrients to cells in plants. This is due to the water's capillary action; the ability of a water to sample to continuously crawl unto another body because of its adhesion. It also acts as the backbone for the structure of blood (blood also contains iron, copper and so on). Interestingly, the human body is almost 67-70 % water.