Water Planet

Looking down at our planet from outer space, most of what you see is water. About 71% of Earth’s surface is covered by ocean, which is why Earth is sometimes called the Water Planet. But that name is a little deceiving when it comes to our ability to supply clean drinking water to the nearly seven billion people on the planet.

“Water of love, deep in the ground
But there ain’t no water here to be found
Someday baby when the river runs free
It’s gonna carry that water of love to me.”
—Mark Knopfler, Dire Straits

   Oceans account for 97.25% of our water. The other 2.75%—fresh water—is divided up between glaciers and polar ice (2.04%), ground water (0.68%), lakes and rivers (0.01%), and the rest in clouds, vapor and precipitation.

Visualizing Earth’s water supply as spheres.

   Think of it another way. If you could gather up all the water on the planet into a sphere it would have a diameter of 1,380 km, or about 40% that of the Moon. Pretty massive, right? But how much of that is drinkable? First lets remove all the salt water. That leaves us with a sphere that is 458 km in diameter. But most of this water—almost three-fourths of it—is locked up in glaciers and polar ice. If we remove that, our sphere of drinking water shrinks considerably, down to 265 km in diameter. Yet most of this water is still not available to drink, being trapped underground. The sum total of all the drinkable fresh water, available in lakes, rivers, and other reservoirs, would make a sphere just 66 km in diameter. So even though we live on the Water Planet, its easy to see why we have a Water Problem.
   Take Lake Mead for example. Fed by the mighty Colorado River, it’s the largest reservoir in the United States.  Since 2000, its water level has steadily declined from 370 m to a low of 330 m in November of 2010, only two meters above the critical level that would automatically trigger water rationing for much of the southwestern United States. And according to a 2008 study done by the Scripps Institution of Oceanography, there is a 50% chance that Lake Mead could run dry by 2021 if climate change and use projections hold true.