You probably know all animals require water to live. Humans drink fresh water and get water from the foods we eat. If we eat foods that contain enough water, we could get the water we need without actually drinking it. If we drink seawater the salt overwhelms our kidneys, essentially making us thirstier. However, whales ingest some seawater with the foods they eat, yet are fine. Just like us, whales need fresh water in order to live. They get most of this water from the food they eat (krill, fish, or plankton). Whale kidneys are made to extract water from their food and possibly some seawater. This is similar to the way terrestrial desert animals get water from their food.
Water Intoxication | Sports Drinks Versus Water