Water is important for all living organisms as many substances are able to dissolve in it (it is a solvent)
This makes it incredibly useful and essential for all life on Earth
Water is important as a solvent in the following situations within organisms:
Dissolved substances can be easily transported around organisms - eg xylem and phloem of plants and dissolved food molecules in the blood
Digested food molecules are in the alimentary canal but need to be moved to cells all over the body - without water as a solvent this would not be able to happen
Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine
Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells