Seawater
From Glossary of Meteorology
seawater
The water of the seas, distinguished from freshwater by its appreciable salinity.
The distinction in usage of saltwater and seawater is not very sharply drawn. Commonly, seawater is used as the antithesis of specific types of freshwater, as river water, lake water, rainwater, etc., whereas saltwater is merely the antithesis of freshwater in general.