the oceans are 100% water... lol If you're talking about pure water, without salt or liquid waste, probably about 97%... I'm not sure what the salt-to-water ratio is, but it does fluctuate depending on what part of the ocean you're drawing your sample from.
80 percent evaporates from the ocean. Incorrect !!! All water in the water cycle of Earth evaporates from oceans and works its way back to the ocean. Evaporation from rivers, lakes, ponds etc. is a temporary stage of the overall trip back to its origin in the oceans.
It you mean in specific, "The Pacific, Atlantic, Indian, and Arctic Oceans." In general, probably "Oceans, rivers, lakes, and streams. You also would try groundwater,precipitation,surface water, and sea water.
Under-GROUND oceans? Probably not; the current estimates for Europa indicate that the surface is probably ice, with perhaps oceans beneath the ice. If the oceans are made of water rather than some more exotic liquid, then there's at least a possibility that life might exist in that ocean.