FRESH WATER FOR ARID LANDS—JENKINS 287 
well as at home, bringing about a valuable international exchange of 
information on saline-water conversion. The strength of this mutual 
interest became apparent in the Washington Symposium [5] on the 
subject held in November 1957, and is evidenced again by the present 
gathering. 
The Washington Symposium confirmed that although we may im- 
prove present distillation processes, much exploratory research is 
needed to develop wholly new approaches to desalting. It is my 
firm conviction that nature has locked away from us temporarily 
one of her most fascinating secrets. From principles of physical 
chemistry and thermodynamics we know that theoretically we should 
be able to get fresh water from the ocean for an over-all cost of about 
10 cents a thousand gallons with reasonable allowances for inefficien- 
cies. Already science has succeeded in reducing the cost to about 
10 times that amount, with considerable promise of further reduc- 
tion to about 5 times or 50 cents. This will make it possible to supply 
water for a number of special new uses, particularly in areas of 
low-cost labor and materials. But to unlock this secret of nature 
so as to serve general irrigation uses will take a scientific development 
comparable to that which uncovered nuclear fission and fusion. Its 
accomplishment may well rival nuclear energy in its effect upon the 
world economy. 
How best can we solve this problem? Not knowing which approach 
may turn out ultimately to be the best, we must pursue all possible 
and logical leads. Many new approaches should be investigated, 
and effort should be devoted to such fundamental studies as the mech- 
anisms by which salt-water phreatophytes select nitrate and phos- 
phate ions but reject sodium and chloride, as well as to the functions 
of the kidneys in maintaining salt balance in the human, animal, or 
fish systems. Fortunately, some research is being directed to ap- 
proaches of this type. 
In order to separate water from a salt-water solution, we must 
expend energy [6]. The minimum theoretical thermodynamic energy 
needed to separate water molecules from salt ions can be calculated 
from the experiment shown in figure 2. At the same temperature and 
pressure, more water molecules will change into the vapor phase 
from the fresh water (left) than from the salt water (center). By 
compressing the vapor above the salt water to the same pressure as 
that above the fresh water, it can be made to condense to fresh water 
(right). The energy required is just equal to the energy that binds 
the water molecules to salt ions. For sea water this minimum re- 
quirement is 2.8 kilowatt-hours per 1,000 U.S. gallons. Inventors’ 
claims involving energy requirements less than this minimum are 
bound to be false. 
