I am not a biologist, but my impression is that the only kind of life we have ever seen has been based on water. We do not know what other kinds of life are possible. Even exotic anaerobic bacteria contain water, even though their respiration process has nothing to do with the oxygen cycle.
Biologists now speak of 'Xerophiles' which need little water to survive. For example in a review article by Dave Roberts (Department of Zoology, The Natural History Museum, London):
The driest regions can support eukaryotic life, for instance in the lichens which grow on stones, or even in the Negev Desert (Palmer & Friedmann, 1990). However, the ability to grow in conditions out of liquid water seems to be restricted in the microbes to the fungi. It is an everyday observation in food spoilage that the first colonisers are normally fungi, especially of foods with reduced water activity as a means of preservation (jams, marmalades and similar conserves). The fungi are also able to utilise the filamentous habit to grow through regions unsuitable for growth including bridging air spaces in the search of suitable habitats. The capacity to distribute nutrients through the filamentous colony is clearly an important adaptation for this niche as well as the capacity to withstand desiccation whilst growing out of water.
Still, these life forms require some water in their chemistry, and no organisms have yet been found that don't need it at all.
Copyright 1997 Dr. Sten Odenwald
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