There are a number of other possibilities. Dr. Isaac Asimov, a biochemist, suggested that on certain large planets, plants might split water into oxygen and hydrogen, and use the oxygen, combined with ambient methane to make carbohydrates.
Animals, possibly including intelligent ones, could consume those plant carbohydrates, and breathe the hydrogen, exhaling water vapor and methane, which the plants could use.
A veritable cycle and an alternate biochemistry.
Life based on silicon is not out of the question, either. In combination with oxygen, it can form complex chains, and giant molecules, as silicones. These have the basic form of alternating silicon-oxygen-silicon-oxygen 'backbones' with a methyl radical like CH3 attached at each silicon atom.

like some of you answered...there are some possibilities to have extraordinary Life, but water is abundant in Space...to using water & carbon & it's compounds usually results in our way of breathing...
not our genome, or figure...but same principle of breading atmosphere...
;)

some creatures do exists that are Arsenic based:
http://news.nationalgeographic.com/news/2010/12/101202-nasa-announcement-arsenic-life-mono-lake-science-space/
but haven't found to be more than bacteria based...

also, MW - do you have a link to that Asimov text about different lifecycle?!

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non-profit org. Play4Life in Zagreb, Croatia, EU

but water is abundant in Space

I rather think not. I would like to see some evidence for that.

Read books...about Space, star formation & types, planet formation, comet & planetoid composition, etc.
;)

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non-profit org. Play4Life in Zagreb, Croatia, EU