Salinity is a measure of saltiness. The more salt in a body of water, the higher its salinity. Fresh water is less than 0.1 percent salt. Ocean water is, on average, about 3.5 percent salt. The Dead Sea has famously high salinity. It’s about 30 percent salt! All that salt makes the water extremely dense. As a result, swimmers can easily float in it.
Water that is too salty is not safe to drink. It also is not safe to use for watering crops or many other purposes. But salt water in the oceans makes up about 97 percent of all water on Earth. Some other sources of water, such as groundwater, can also have very high salinity. To tap into these water sources, engineers are coming up with new ways to filter salt out of water. This process is called desalination.
In a sentence
An estuary is a place where a freshwater river meets the ocean, where water has a higher salinity.