A quick google search on “Water as the Basis of Life” will come up with all sorts of unsubstantiated claims and calls to action to stop polluting. I want to answer the question “WHY is water the basis of life as we know it?” (Please note: This is not a complete answer and I welcome additions in the comment section!)
The chemical structure of water is H2O meaning that for every Oxygen atom there are two Hydrogen atoms. Because of the electron structure of these atoms, both hydrogen atoms sort of get pushed to one side of the molecule (see picture). The angle between the two hydrogen atoms is 104.45 degrees. Unlike many other compounds, this somewhat awkward angle means that water doesn’t stack neatly in solid form. This is why water is less dense as a solid than it is as a liquid. The great majority of people will say, “So?” The real point to make here is that if ice sank, an entire body of water could freeze in the course of a winter and the lower layers of that body of water would never melt. The great mixing pot of our planet (the ocean), which threw together self-replicating molecules and vesicles to create the first cells, would never have existed at all if ice sank.
Water is one of many compounds that form Van der Waals bonds. Van der Waals bonds are weak electrostatic attractions between molecules. It takes a relatively large amount of energy to heat water until the Van der Waals bonds break, so heat gain/loss happens relatively slowly. This (and an atmosphere) is what keeps our planet at relatively stable temperatures, so that life has a relatively stable temperature platform to operate from.
The final point I’d like to make about water has to do with recent research into astrobiology. Scientists have discovered that common (non-water) compounds in comet-ice, when subjected to high rates of radiation, form Polycyclic Aromatic Hydrocarbons. These PAH’s are very similar to DNA/RNA and life on earth probably evolved because these compounds were present in the comets that bombarded earth early in her history. This is a really cool discovery all by itself, but it also supports my idea that life is water oriented, even life on other planets. Additionally, this means that life on other planets will have a genetic information storage mechanism similar (but probably not identical) to our DNA.
I have presented a couple of the many characteristics of water which make water a likely starting point for life on other planets. I welcome further additions/opposing hypotheses in the comment section so long as they are polite and relevant. Tune in next time I post for an explanation of why I think the aliens will be multi-cellular with differentiated tissues!