Water necessary for life ? Perhaps not - back in the long ago, I remember someone talking about a theory of life based on silica rather than carbon. In fact there are diatoms with silicious shells but even then the little critters are based on carbon and need water to survive. So at this point a silicon based life form is still a theory.

Although It may be possible that some life form or other might not require water to survive it doesn't seem likely to me.I think it is a matter of what is likely and what is detectable with a limited budget rather than what is necessary.