Water is necessary for all "life as we know it". There could be configurations we don't know about that allow life to form from radically different constituents

Water is necessary for all "life as we know it". There could be configurations we don't know about that allow life to form from radically different constituents. The universe is big enough to allow for the possibility, but it's so theoretical that we have no framework for understanding how these kinds of exotic lifeforms would work or how to look for evidence of their existence. So while we shouldn't exclude the possibility, "life as we know it" is the most sensible place to start.