From long term records of annual rainfall we get 53" for P. The USGS
measures stream flow and ground-water discharge and they estimate an
annual amount of about 36" for Et.
thus, 53" = 36" + R, or R = 17"
This 17" is the average annual "water crop" that is potentially available for
Each inch of water over a square mile equals 17. 4 mgy (million gallons per
year). -With 17" available we have 295. 8 mgy "new" water for our one-time
use for each square mile in the District.
This seems a staggering amount of water, however, we cannot hope to cap-
ture all of it. If we harvest half of it, we're doing exceptionally well. We
can expect, by carefully planned withdrawals, to actually capture about one-
third. The remainder of the "crop" must be saved to keep our lakes and
streams reasonably supplied with water --for navigation; for pleasure (boating,
swimming, fishing); for dilution of waste and transporting of wastes; for
sufficient flow to keep salt-water of the Gulf from invading our fresh waters;
for beauty, of the landscape, and many other purposes.
This one-third or 98. 6 mgy or 270, 000 gallons per day is what we have to
use for each square mile of the District. Any time we exceed this amount
we either dip into our water bank savings, or we must use that 98. 6 mgy
* over more than once, perhaps several times.
The USGS in its 1965 water use evaluation of the Nation's uses of water
showed the daily usage per person to be 1,600 gallons per day. They got
this by dividing the total gallons of water per day withdrawn from streams,
lakes and aquifers in the U. S. by the total population of the U. S. Thus, it
includes water for irrigation, manufacturing, light and heavy industrial
uses, cooling, flushing, fire-fighting, and all other municipal and home
uses. But it does not include water used for such purposes as generation
of electricity by hydroelectric plants, for such uses do not deplete the supply.
I doubt that in our District we use this much, but I do believe that with our
heavy withdrawals for the phosphate industry and for irrigation of citrus
Sand vegetable crops we use about 1,000 gallons per person per day (1,440
gallons would be 1 gpm), or each square mile would support 270 persons.
*You can readily see that the densely populated areas cannot support them-
selves even now.
On a District-wide basis, we estimate our population as 150 persons per
square mile. Therefore, we are now using about 55% of the available water
crop. By doubling the population, which has been forecast for this area by
About 1985, we will then be using not only all of the annually available water
crop but more -- we'll be drawing out of the water bank. ..
What remedies can we see to rectify this challenging situation? How may
we live within the water budget? Or can we ? I hope to be able to answer
these and other related questions for you in next month's issue of "The