Chemicals of Life
It is a liquid = good can dissolve things. It is a polar molecule - is has an unever distribution of charge, and is said to have polarity. This makes it a good solvent for polar solutes. It also has a hydrogen bond.
A substances heat capacity, is the amount of energy(joules) required to raise its temperature by 1oC. Water has a hgh heat capacity. So it generally doesn’t vary in temperature too much - not greatly affected by environmental heat changes. Most organisms and biological processes can only live/occur within a small range - making water ideal.
Water has a very high surface tension - the force that causes the surface of the water to contract to occupy least area. This is very important, because it plays a major role in getting water up tall trees/plants. It also allows some insects to stand on the water.
On freezing it increases volume and decreaes volume - which is not common. This means that in winter, the ice will form at the top, while warmer water resides underneath - allowing organisms to survive. If water froze at the bottom(ie more dense), then most of the ocean would be frozen.
If it were opaque then light would not get to primary producers. It also allows organisms to see.