There is a hard limit on the number of atomic elements, and an even smaller limit on the number of soluble compounds that facilitate chemical reactions, and water is demonstrably both the best and the most common in the universe.
So while it may be possible for life to exist without water, any alternatives should be reasonably expected to be even more rare than water-based life
There's a reason life is carbon-based, and it's not random. It's the only element that works, due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable. There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy. And no other elements have any hope. If you have carbon-based life, you need water as solvent and medium.
It's a pretty safe assumption that all life requires water.
> due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable
Well, the thing is that all of those are environment-dependent.
We do have data on a somewhat diverse set of environments, and it's enough to confirm what we knew about the flexibility of carbon. But it's not enough to disprove the alternatives.
1. xbmcuser’s point:
They challenge the anthropocentric (Earth-centric) assumption — “we only know life as we know it.” Philosophically valid, but scientifically weak without proposing a viable alternative chemistry.
2. joshuahedlund’s reply:
Grounds the argument in chemistry and probability.
There are only ~90 stable elements → a finite combinatorial chemistry space.
Among possible solvents, water is the most abundant and chemically versatile (dipolar, wide liquid range, high heat capacity, good at dissolving ions and organics).
→ So even if other solvents can work (like ammonia, methane, formamide), the odds heavily favor water-based life.
3. caymanjim’s addition:
Brings in carbon’s unique valence behavior:
4 valence electrons → can form stable, complex chains and rings.
Bonds are strong but not too strong → dynamic yet stable biochemistry.
Silicon (next best candidate) forms brittle, static lattices and poorly soluble oxides → bad for metabolism.
→ Therefore: if life is carbon-based, water is the only sensible solvent.
But when you dig down deep on theories like that it just doesn’t make sense from a chemistry or physics standpoint. Everyone saw that Star Trek episode about silicon based life and ran with it as being possible. It’s just a show.
