Water, water, every where, Nor any drop to drink?
In one of the more vexing ironies about human life on Earth, we rely on water for life, yet 96.5 percent of all Earth's water is sea water, which we cannot drink. Where did we go wrong??
But what about whales, dolphins, sea lions and other marine mammals? Did they figure this out a little better than we did? They live in saltwater; but do they also drink it?Marine biologist Robert Kenney of the University of Rhode Island explains that some marine mammals have been known to occasionally partake in the salty stuff, but they rely on other options. The often get the water they need from the food they eat, very clever. The New York Times writes that they can get low-salt water from dinner: "Whales, for example, have the specialized kidneys but need far less water than land mammals. Whales get water mostly from the small sea creatures, like krill, that form much of their diet."
Marine mammals can also produce non-salty water on their own from the metabolic breakdown of food, says Kenney, as "water is one of the by-products of carbohydrate and fat metabolism."
Even so, marine mammals get a lot of salt ... and they have ways to get rid of it. Seawater is three times saltier than blood (of both terrestrial and marine invertebrates). So sea animals get rid of extra salt by producing super salty urine. Kenney explains that in some seals and sea lions, for example, their urine contains up to two and a half times more salt than seawater does and seven or eight times more salt than their blood.
Some seals will eat snow to get their fresh water; meanwhile, California sea lions can get enough water from the fish they eat and can live without actually drinking any fresh water at all.
And while you might think that seabirds have it easier, given that their gift of flight can take them out of the sea and to freshwater sources, they still have some pretty nifty tricks up their wings. As The Times explains, "seabirds have special organs called salt glands above their eyes that extract excess salt from the bloodstream and excrete it through the nostrils."
It will be interesting to see if over time we could start adapting to saltwater a little better, especially given that we're screwing up our freshwater supply so magnificently. Maybe future humans will have salt-extracting organs above our eyes! But in the meantime, maybe we should just take care of Earth's 3.5 percent of precious freshwater ... we can't all be whales and dolphins.