As a liquid it is the basic fluid of animal blood, tree sap and cell plasma. Yet when water evaporates, it no longer forms combinations. This allows it to diffuse in the atmosphere so it doesn't stifle life by lying on the earth's surface as an unbreathable gas. Water is also a universal solvent, dissolving the necessary solid chemicals so they can circulate in the bloodstream, plant sap, and living cells. All other liquids which can dissolve a comparable number of chemicals are highly corrosive and deadly to living things.
Water is unusual in being able to absorb a large amount of heat for a given change in temperature.
As a result it moderates the climate of the earth and helps stabilize the body temperature of animals. Like few other substances, it expands rather than contracting on freezing. Truly water is a most amazing substance. The earth's environment is unique in the solar system and at least very rare in our galaxy. The temperature varies substantially from pole to equator, summer to winter, and from the Dead Sea to Mt. Everest.