Saltwater is water that contains dissolved salt, like the water in oceans and seas. When you swim in the ocean and accidentally swallow a mouthful, that salty taste comes from the minerals dissolved in the water. About 97% of Earth's water is saltwater, which covers roughly 70% of our planet's surface.

The salt in saltwater makes it very different from the freshwater in lakes, rivers, and streams. You can't drink saltwater because the salt would dehydrate you rather than quench your thirst. Fish and other sea creatures that live in saltwater have special adaptations that let them handle the salty environment. If you put a freshwater fish like a trout into saltwater, or a saltwater fish like a tuna into fresh water, it wouldn't survive.

People use the word as an adjective too: saltwater fish, saltwater pools, or saltwater taffy (a candy originally made in seaside towns). Some people keep saltwater aquariums at home, though these require more careful management than freshwater tanks because ocean creatures need precise salt levels to stay healthy.