There’s actually nothing carved-in-stone anywhere in Science which dictates that all forms of life throughout the Cosmos absolutely “must have Water.” H2O is the ‘universal solvent’ to undergrad students, it’s also a sufficiently robust & ubiquitous molecule (esp. rocks/meteorites/comets/hydrosphere), and it nicely (conveniently/familiarly for an undergrad) hosts Acid-Base chemical reactions, as well as Redox teactions, & Photochemical reactions; but a chemist could certainly conceive of other solvents/reagents that might fit-the-bill elsewhere, such as NH3.