Which type of salinity is generally considered to be freshwater?

Freshwater is defined by its low salinity, which is typically close to 0 parts per thousand (ppt). In aquatic environments, freshwater refers to water bodies that contain minimal dissolved salts. The threshold of salinity for freshwater is usually considered to be less than 1 ppt, but for the purpose of this question, 0 ppt accurately reflects the concept of freshwater.

Salinities of 15 ppt, 35 ppt, and 50 ppt would all be categorized as brackish or saltwater, which are associated with higher concentrations of dissolved salts. For instance, 15 ppt is usually representative of brackish water, where freshwater and seawater mix, while 35 ppt is characteristic of typical ocean water. Salinities as high as 50 ppt would be highly saline and typically seen in certain marine environments or artificially created conditions, which are far from freshwater standards.

Therefore, the value of 0 parts per thousand correctly identifies the conditions under which water would be classified as freshwater, thereby confirming its accuracy as the answer.