Water is extreemly common in the universe. It also enables a lot of useful chemistry that complex molecules need. In turn it is reasonable to expect water is part of all life - not a given but most of the other options rely on something far less likely to occure.

This assumes there is life. Not a debate I'm touching. Although if there is physics is against us ever discovering it. Even if earth is an extreem outlier in taking so long to develop intelligent life and every other star has it in a few hundred years few will never detect another lifeform