>>11672931So it's not a global assumption but it is a common one for some good reasons.
1. It's a good solvent
2. It has a lot of complex emergent properties in phase changes
3. It works well as a hydrogen ion donor and acceptor without needing some wild pH swings
4. Lots of unique chemistry relies on water as an intermediate
5. It has strong inter molecular interactions
6. Good geometry for symmetric reactions
Those are just off the top of my head. Water is a unique substance that we still don't really understand all that well. I wouldn't be shocked if there were other solvents capable of forming life. But my guess would put water as the most likely candidate for the formation of life due to it's diversity of properties.
