There is a way to differentiate between the turtles that live solely in water, the ones that only live on land, and there are turtles that do some of both. The best way to understand the answer is to understand turtles as a whole.
Turtles are one of the oldest reptile groups in prehistory. Many people refer to all Chelonia as turtles, but you can really break it down a bit further if you want to be scientifically accurate. Turtle is most accurately used when referring to Testudines that live exclusively in water except during the brief shore visit laying of eggs. Turtle is most commonly used for marine or sea turtles and not freshwater or land-dwelling turtles.
Tortoise is a more accurate way to refer to Testudines (or Chelonia) that live almost exclusively on land. Tortoises do not swim.
Not as many people use the word Terrapin, but it’s loosely used to refer to turtles that spend some time on land and some in the water. Most animals known as terrapins live near swampy water and love a wet environment even though they aren’t technically water-dwelling turtles that live and swim underwater for life.
The type of turtle that will best fit the description is the terrapin. Sea turtles never come back to land after hatching, other than just the females when they come back to nest. Tortoises live exclusively on land. This leaves only the terrapin, which spends most of their time in the water, but also returns to land to bask in the sun and rest.