Oceanography

Population pressure, growing individual water use, severe local water problems, and a growing consciousness of the far-reaching effects of some pollutants force us to look at the Earth’s water resources with an eye to measurement.

If we regard the total water in the oceans, in ice, in streams, lakes and rivers, and underground, as an available total supply, the water problem seems to disappear. When 71% of the earth’s surface is covered by oceans averaging two and a half miles deep, how could there be a water shortage? The great Pacific Basin covers half the globe; there were times in the flights of the earth-circling astronauts when they could see almost half the earth at once and yet see only an ocean, dotted here and there with a few tiny islands.

One way to try to visualize the total amount of water is to make it into ice cubes, thirty miles on an edge, each one big enough to cover up most of the city of New York and extending up to the limits of the atmosphere. We would have to melt 12,000 such cubes to make the oceans. Compared to the oceans, the amount of water at anyone time in all the other “reservoirs” is tiny. We think of streams and lakes as important but they contain much less than 1 percent of the total amount of water on earth. We hear of the dire consequences of melting all the glaciers, which would raise sea level two hundred feet and destroy hundreds of coastal cities, yet this two hundred feet on a global basis is only 1 Y2 percent of the depth of the oceans. Underground water, water trapped in or moving through the pores of rocks, is the second greatest supply of water and may be as much as 10 percent of the oceanic total. We estimate that all these reservoirs together contain four hundred billion, billion gallons of water.

Another way to look at the total supply is to divide it by the number of people who need to use it. A quart and a half per day is required for sheer survival of every human being. There are 3.5 billion people on earth; what is each one’s share of the total? The answer is somewhere in the vicinity of 120,000 million gallons of water for every human being now in existence. If each person could have a tank to hold his share of water, the tank would be half a mile on each side. If each person’s tank were to be filled from a mixture of sea water, river water, lake water, melted glaciers, and underground water, it would be almost as salty as the ocean itself for 88 percent of all water comes from the ocean basins and would dominate the mixture. So we see that water supply is not a problem of total-at least not for a long time-but of water suitable for various needs and available for use.

Moreover, fresh water has a thousand uses. Water is needed for drinking, for washing, for plumbing, for air-conditioning, for swimming pools, for irrigation, for industry, for boating and fishing and swimming, for pure scenic enjoyment, for transportation, and for the raising of food of any kind. For each use the water requirements differ and for each type of water the supply varies.

Drinking water, if it is to be used continuously with no harmful effects, must fulfill a great number of requirements. It cannot even be perfectly pure, for many of the elements needed for good health come from the dissolved minerals in drinking water. If only pure water is drunk it acts somewhat like a leaching agent and robs the body of essential salts as it passes through our systems. Nor can it contain more than about one tenth of one percent dissolved minerals before it develops a strong, unpleasant taste, and begins to upset digestion.

We are the most complex water treatment factories that can be imagined, taking in enormous quantities of water, extracting and using the elements we need, then expelling them in many ways: through skin, kidneys, intestines, through mouths and noses. When the chemical elements are taken in they are segregated appropriately into the different body fluids and sent on to perform their proper functions. Calcium, strontium, and phosphorus are sent to the bones, potassium is enriched many times within cells, iron goes into red blood cells. The human factory is pretty well geared to a diet of average stream water, but despite the flexibility of the system, a marked increase of almost any element in the water supply causes impairment of the functions of the factory. The dynamic and current nature of the human factory is almost unbelievable. If a person is completely immobilized, he begins to excrete more calcium than is taken in. His bones literally begin to dissolve and do it so fast that the calcium cannot be excreted fast enough to prevent its climbing to dangerous levels in the blood. Astronauts exercise regularly in flight; one of the reasons is to prevent calcium toxemia, as it is called.

“Average” drinking water contains about two hundredths of one percent of dissolved minerals (the same as 200 parts of minerals in a million of water, or 200 ppm). A quart boiled to dryness leaves only about one two-hundredth of an ounce of solid residue behind. This residue is made up mostly of three “salts”: common salt (sodium chloride), limestone (calcium carbonate), and gypsum (calcium sulfate), plus some silica (silicon oxide). There are traces of magnesium and potassium salts as well, and miniscule amounts of almost every other element known.

The proportions of the three chief salts differ markedly from place to place; water reflects the compositions of the rocks and soils through or over which it has passed, collecting dissolved minerals as it goes. High sodium and chloride and calcium have little influence on the taste of water, but when the sulfate content goes up water takes on an unpleasant astringent quality. Often when sulfates are high, magnesium is too. Many waters in the arid and semi-arid western states contain a lot of magnesium and sulfate. The combination wreaks havoc with the intestinal tracts of tourists, commonly having a strong laxative action. But the adaptability of the human body is remarkable; natives of the magnesium-sulfate water areas accommodate so well to their drinking water that they not only live happily with it, they may complain that the waters of other places are bland and uninteresting.

It is the flexibility (within limits) of the human body that makes it difficult to say exactly which dissolved minerals and what amount in the water supplies are safe or beneficial. The U.S. Public Health Service sets up standards for the permissible amounts of the various elements in the public water supplies. The task is a continuing one, for careful long-term records are needed to know whether any given substance is good or bad. Because waters differ so much and contain so many different elements, the job of isolating the effects of a given element requires vast amounts of information about the medical histories of the inhabitants of regions served by a particular kind of water.

There are tests for toxic elements like lead and arsenic. There are tests for radioactive substances. There is a growing list of tests for new compounds like insecticides.

One of the surprising bits of information that comes from reading about the limitations of water composition for the good health of fish, for boiler feed, or for irrigation, is the relative liberality of the standards for drinking water. We seem to be more adaptable than many species of animals and plants in the range of substances we can drink and still survive in good health. We think of ourselves as being delicate; it may be that because of our adaptability we would be among the last survivors in a world of uncontrolled degeneration of water quality.

But no matter what our intake of water we all need a minimum amount for survival. We can go for perhaps eighty days without food, but only ten days without water. A 1 or 2 percent variation in body water is painful; with a loss of 5 percent the skin shrinks, the mouth and tongue become dry and hallucination begins; a 15 percent loss is fatal. We can also have too much water, causing nausea, weakness, mental confusion, disorientation, convulsions and even death.

The body regulates itself quite well and keeps a remarkably constant composition, 70 percent of which is water.