Water (H
₂O) is a polar compound that is an important solvent for polar molecules in chemistry, and known as the "universal solvent" for its ability to dissolve many substances.^[1] At room temperature, it is a tasteless and odorless liquid, nearly colorless with a hint of blue. It is commonly found in its solid, liquid and gas forms in nature.

Water has hydrogen bonding and is strongly polar. This polarity allows it to separate ions in salts and strongly bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form, a relatively high boiling point of 100 ºC for its molar mass, and a high heat capacity.

Water is amphoteric, meaning it can act as both an acid and a base; it can also self ionize to produce H⁺
and OH⁻
ions. This means the product of the concentrations of H⁺
and OH⁻
has to be constant.

Because water is a very good solvent, water is rarely pure and some of its properties may vary from those of the pure substance. However, there are also many compounds that are essentially, if not completely, insoluble in water, including fats, oils and other nonpolar substances.