Do Whales Drink Sea Water?

Some marine animals, such as seals and sea lions, spend part of their time in the ocean, but come out of the water too. Others, like manatees and dolphins, also swim in rivers or close to shore where they may find fresh water. But whales spend all of their time in the ocean. Since their bodies need water to survive, scientists believe it's reasonable to assume that whales do drink sea water. An adult blue whale takes up to 10,000 gallons of water into her mouth at one time while she's eating. She doesn't drink all that water, though; the baleen in the whale's mouth filters the food and the whale pushes most of the water out.

The salt content in whales' blood and other body fluids is about one-third as salty as sea water, similar to that of other mammals. That means when the whale drinks salt water, her kidneys must get rid of all that excess salt. The whale's kidneys are built for this job. They are super-sized, capable of filtering large amounts of water and separating most of the salt. They also have extra long tubes to hold large quantities of the salt-concentrated urine, which is then excreted. Other sea mammals seem to have similar kidney function, capable of filtering out large amounts of salt, whereas land animals and humans do not.

Whales don't get all the water their bodies need by drinking sea water. They also get water from their food. A whale's diet consists mainly of fish, which have a salt content similar to that in the whale's body. When her body breaks down the food, water is one of the by-products. So the water that is derived from her food is not extra salty.

Whales don't sweat, so they don't lose water through perspiration. They're not out baking in the hot sun, either; they're under water most of the time. And unlike land mammals, such as humans, whales don't lose water when they breathe. So pound for pound, whales don't need to take in as much water to stay healthy as other species do. Thank goodness, since many whales weigh as much as 50 tons.