Salt and Water

noaa.gov

Behold the ocean.  As you no doubt learned in school, oceans make up 71 percent of the earth's surface.  This is true, but it seriously understates the amount of saltwater on the earth.  

Here are the facts:

     -- 96 percent of the earth's water is saltwater.

     -- 4 percent of the world's water is freshwater.  Of that, more than two thirds is held as frozen water in glaciers and ice caps. Much of the rest is vapor in the atmosphere

     

     --  The remainder, less than 1 percent of all the water on earth, is freshwater available for the sustenance of land animals, plants and, today, more than 7 billion human beings. 

In early times, humans located their communities near rivers or lakes or wells, for the obvious reason. 

As human engineering allowed for diversion of water, the settlement of large cities in other places became possible.  Recently I have discussed how this came to pass in two American cities, San Francisco and Los Angeles.   The phenomenon was a worldwide one, however, and certainly not limited to cities on the American West Coast.

Engineering progress also allowed for deeper excavation of wells and, with it, increased agricultural production that fed growing populations.

Over thousands of years, several problems arose.  First was that climate changed from time to time and from one area to another.   It turned out that droughts were unpredictable elements in climate cycles.

The second problem was that, also over time, industrious humans drew water out of underground wells faster than rains could replace it.

There are not easy solutions to problems like these.  Cities and states are taking the obvious steps -- limiting household water use, recycling gray water and promoting dry-weather plantings.  

Another less obvious but promising step is desalination -- taking the salt out of some of the ocean water.  This might provide insurance against severe droughts and reduce the raiding of inland water sources that are essential for animal habitat and agriculture. 

This is actually a very old idea, dating at least to the time of Aristotle.  His thought was similar to the one sketched below.  In it, ocean water is collected in a container, evaporated by heat and then condensed into a tank, leaving the salt behind.

usgs

I am not old enough to have discussed this procedure with Aristotle, but my guess is that he may have been at least as eager to collect salt for the preservation of food as to gather fresh water for drinking. Who knows?

In any event, the idea offers possibilities.  Groundwater tables have been drawn down to dangerously low levels in parts of the Americas, Asia, Africa and Australia.  Some countries have committed major resources to desalination, and even slow, slow America is starting to dip its toe into the water.

More about that later.