Why is water essential to life on a chemical level?

Well Water is essential to life for a number of reasons. It is a useful solvent that exists as a liquid at the ideal range of temperatures for life as we know it on Earth, behaving as a perfect medium across which biochemical reactions can occur. Your cells transport resources across the spaces within and between them facilitated by this medium, just as your blood serves as the ideal medium for transporting oxygen-carrying corpuscles and a rich soup of nutrients, hormones, and even waste products being sent for filtration. The very structure of your tissues is reliant upon water content; consider the difference between a fresh loaf of bread and a stale (dry)one that can be crumbled between the fingers. Plant cells, just like animals cells, require hydration to function, too. In fact, right down to unicellular life forms, life as we know it on this planet relies upon water existing as a liquid in order to function on a biochemical level. I hope that helps you.