You need water to generate steam to turn a turbine and make electricity (same for coal, natural gas, fusion). However, many advanced reactor designs do not use water for the reactor coolant itself, unlike light water reactors that do. They use gas, molten salt, or liquid metals. As a result, you can get to quite high temperatures useful for process heat, such as hydrogen production. Direct desalination might also be doable, the issue/question being on the design of the non-nuclear side of the plant.

A lot of Gen IV designs are in the process of commercialization now, with demonstrations slated for later this decade.