Some plants can survive for many years as seeds. Insects and unicellular life forms can also wait out drought. Sooner or later, however, liquid water is necessary. Survival is essential, but it is not all of life. Without growth and reproduction, life is on hold, not progressing.
Salinity can also interfere with an organism's use of water.
Fresh water fish cannot live in the ocean, and land plants watered with sea water will die. The excess salt in briny water pulls water out of the organism and dehydrates it. If you put a salt water fish in fresh water it will die, too, because the organism will retain too much water in its cells. Plants use sunlight for photosynthesis. Lack of light in caves and under deep water make these environments unsuitable for photosynthesizing plants.