LEANING RIGHT-We all stand around with baited breath and turn our parched faces skyward as drops of needed rain from heaven above fall on Southern California. Let’s look at how much water is out there and later look at current desalinization and recovery efforts.
About 70% of the earth’s surface is covered with water of which 97% is salt water and, of course, we cannot drink it. Less than 1% is fresh water.
How much water is there on, in, and above the Earth?
The drawing above shows the blue sphere representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that this water sphere looks so small? It is only small in relation to the size of the Earth.
This image attempts to show three dimensions, so each sphere represents "volume." The volume of the sphere, representing all water on, in, and above the Earth, would be about 332,500,000 cubic miles (mi3) and be about 860 miles in diameter. This equates to roughly 40 cubic miles of water for each human on earth.
Water is on and in the Earth -The vast majority of water on the Earth's surface, over 96 percent, is saline water in the oceans. The freshwater resources, such as water falling from the skies and moving into streams, rivers, lakes, and groundwater, provide people with the water they need every day to live.
Water sitting on the surface of the Earth is easy to visualize, and your view of the water cycle might be that rainfall fills up the rivers and lakes. But, the unseen water below our feet is critically important to life, also. How would you account for the flow in rivers after weeks without rain?
In fact, how would you account for the water flowing down this driveway on a day when it didn't rain?
The answer is that there is more to our water supply than just surface water, there is also plenty of water beneath our feet.
Even though you may only notice water on the Earth's surface, there is much more fresh water stored in the ground than there is in liquid form on the surface. In fact, some of the water you see flowing in rivers comes from seepage of groundwater into river beds. Water from precipitation continually seeps into the ground to recharge the acquifiers, while at the same time water in the ground continually recharges rivers through seepage.
Humans are happy this happens because people make use of both kinds of water. In the United States in 2005, we used about 328 billion gallons per day of surface water and about 82.6 billion gallons per day of groundwater.
Although surface water is used more to supply drinking water and to irrigate crops, groundwater is vital in that it not only helps to keep rivers and lakes full, it also provides water for people in places where visible water is scarce, such as in the desert towns of the western United States. Without groundwater, people would be sand-surfing in Palm Springs, California instead of playing golf.
It seems strange that water should be such a scarce resource when our planet is drenched in 326 million trillion gallons of the stuff. But it turns out that less than one-half of 1 percent of it is drinkable.
Out of the rest, 98 percent is oceanic salt water and 1.5 percent remains locked up in icecaps and glaciers. The stark irony of Samuel Coleridge's immortal line "Water, water, everywhere / Nor any drop to drink" is manifest each year in coastal disasters around the world, like Hurricane Katrina, the 2004 Indonesian tsunami and the 2010 Haiti earthquake, as people within sight of entire oceans are threatened with dehydration.
Between droughts, natural disasters and the large-scale redistribution of moisture threatened by climate change, the need for new sources of potable water grows with each passing day. Each year, the global population swells by another 85 million people, but worldwide demand for freshwater increases at twice the rate of population growth, doubling every 20 years or so.
Throughout the world, our most vital resource is under stress from pollution, dam construction, wetland and riparian ecosystem destruction, and depletion of groundwater aquifers, with poor and marginalized populations getting the worst of.
So why can't we convert seawater into drinking water? Actually, we can and we do. In fact, people have been making seawater drinkable at least as far back as the ancient Greeks. But when taken to the scale of cities, states and nations, purifying seawater has historically proven prohibitively expensive, especially when compared to tapping regional and local sources of freshwater.
However, as advancing technology continues to drive costs down and freshwater continues to grow scarcer and more expensive, more cities are looking to seawater conversion as a way to meet this vital demand.
Next week we will look at desalinization and recovery efforts.
(Kay Martin is an author and a CityWatch contributor. His new book, Along for the Ride, is now available. He can be reached at [email protected] This email address is being protected from spambots. You need JavaScript enabled to view it. )
-cw
CityWatch
Vol 12 Issue 97
Pub: Dec 2, 2014
