Water is an amazing solvent. It is liquid at temperatures that don't destroy organic molecules. It exhibits capillary action and surface tension. It starts to expand as the temperature drops below 4C (the calculation is that if water behaved "normally" in this regard, the oceans would be frozen solid from the bottom up and life on earth would be impossible). It has an amazing specific heat capacity. It facilitates chemical reactions in solution better than anything else. It is scarcely compressible in liquid form. It can exist as solid, liquid and gas all at the same time. Lotsastuff. I can't imagine any form of life other than extremely "primitive" that is not predicated on water. And don't get me started on carbon.