Water is practically a miracle in itself. Reasonable range between freezing and boiling, simple structure, polar solvent and non-flammable. The hydrogen bonds

Water is practically a miracle in itself. Reasonable range between freezing and boiling, simple structure, polar solvent and non-flammable. The hydrogen bonds allow lots of interesting processes, and it gets used in many many foundational biological functions as hydroxyl groups. The chemistry of such a simple molecule is difficult if not impossible to replace, and if you have it, the processes that we are familiar with are already efficient enough that there wouldn't be an advantage to not using them. Is it possibly there are configurations of life, such as not using either DNA or RNA? Sure. Is it likely that we wouldn't recognize that it is life? I doubt it very much. Aside from virii which likely devolved from living things rather than forming along side them, it's not hard to make a distinction at all.