It has some interesting properties.
It's an excellent solvent, which means that various complex molecules can be held in suspension in the liquid, free to interact. It's liquid across a relatively wide temperature range, which means these complex molecules are less likely to end up frozen in place or lying on a dry lake bed if the temperature shifts. It has a high specific heat capacity, so it is slow to change temperature, producing a more stable environment. And solid water floats on liquid water (a very unusual property), so an insulating layer forms over freezing water, which serves again to preserve the liquid phase.
It's also cosmically common, which means we don't need to specify unusual conditions for a planet to end up with a watery environment.

And, of course, we know it's possible for life to exist in water, since we have an example of that already.

Grant Hutchison