Explorable Water Gaps

We have learned that the way in which we use water resources at one point can have effects for good or ill on the use and control of water at other points. Flow regulation, for example, may benefit a wide range of activities over extensive areas; surface water used for irrigation often incidentally recharges groundwater aquifers; and cool water eased from from the bottom strata of reservoirs may benefit game fish. On the other hand, wastes introduced into a stream at one point affect the cost, if not the feasibility, of downstream activities; artificial recharge of an aquifer raises the water table and may cause drainage problems at another point; and hot water effluent from a power plant reduces the oxygen saturation level of the water downstream and makes it a less efficient assimilator of organic wastes.

Knowledge of such causes and effects, part of today's slowly acquired learning in the field of water management, is small compared with the vast areas that are still unknown. For all our successes with irrigation and our experimentation with desalination and cloud seeding, we are a long way from making the deserts bloom in any large-scale way. The climatic changes needed to increase evaporation—and distribute fresh water more evenly upon the earth's surface—would involve altering the reflectivity of large areas, modifying the circulation of ocean currents, and otherwise affecting the temperatures of the earth or atmosphere. But we lack the knowledge to understand the total effects of such techniques.

The need for further knowledge in the hydro-science field is far more acute when we lower our sights to smaller, more familiar problems. Gaps in our understanding of the uses of water are becoming increasingly costly in preventing efficient water use both in areas where water is in short supply and in areas where it is plentiful and therefore exploited for many varied purposes. The examples that follow are just a few out of many.

In arid areas, coordinated planning for the use of surface and groundwater storage is becoming vital, largely because evaporation from reservoir surfaces is high and because deltas become infested with phreatophytes—water-loving weed trees and shrubs like the salt cedar—which, like camels, can adapt themselves to drought conditions but soak up water when it is there. Evaporation from reservoirs and transpiration by phreatophytes in the seventeen western states amount to more than twice the water withdrawn for public supplies in the entire United States, and perhaps twenty times the amount that disappears in that use. In the Colorado Basin and the Great Basin, reservoir losses alone are nearly one-third as large as all irrigated agriculture. Methods of controlling reservoir evaporation and phreatophytes are known, but their costs are high and they often yield unsatisfactory results. We need to know much more about how to retain water through transpiration control.

It is equally important to find better means of tracing and predicting groundwater movement and quality, improve techniques for forecasting the capacity of aquifers and recharge areas, and investigate the possibilities of using treated wastewater for artificial groundwater recharge.

On the Colorado River, salinity levels are rising as depletion of dependable flow rises. And in several of the underdeveloped countries in which the United States is sponsoring irrigation schemes, salinity has proved to be the major obstacle. Where rainfall is insufficient for leaching out accumulating water-soluble salts in the soil, crop yields are rapidly reduced. This can necessitate the use of large quantities of irrigation water for leaching salts from the soil.

We still do not know satisfactory ways of controlling salinity conditions and adapting to them—through breeding salt-tolerant crops, for example. And if we could predict the effects of irrigation on water quality, our system planning could be made vastly more efficient.

In the humid regions, the major water problem centers around pollution. But our water purification methods are primitive in relation to the increasing problems of organic wastes and associated algae growth. Left unchecked, algae, thriving on plant nutrients dissolved in the effluent of even treated sewage, can decrease the oxygen content of a stream to a level at which such wastes cannot be assimilated through the stream's natural self-purification process. Appearance, taste, and odor of the water become affected, and fish cannot live. A few people have experimented with harvesting algae from ponds in which rapid growth is stimulated. But we are still a long way from developing methods that will effectively and economically deal with organic chemicals and plant nutrients. Meantime, large-scale plans for river development involving dilution of plant nutrients must be based on arbitrary rules of thumb, since there is disagreement among scientists as to the critical factors affecting algae growth and the effect of algae on oxygen balance.

Methods of separating the wide variety of pollutants from water, it is true, would incur large operating expenditures; yet, were such methods satisfactorily developed, they still would have a comparative economic advantage over devices requiring large investments of capital (like dams) which now are designed to maintain a stream standard at extreme and rarely occurring low flows in order to cope with the pollution such flows would incur.

We need to know more about pollution abatement measures that can be flexibly applied during critical low periods. And, just as importantly, we need to develop the data that would permit a systematic inclusion of waste disposal costs in planning for integrated water resources systems.

Of some 500,000 organic substances known, a substantial number are found in water bodies and in treated water supplies. The vast majority of such trace pollutants occurring in public water supplies is never identified because procedures for detection are difficult and expensive—estimates run from $50,000 to $250,000 a compound. Meantime, we are almost completely ignorant of the chronic physiological effects caused by absorption of minute amounts of chemical substances in drinking water. Because chemical production and use are increasing much faster than population and economic activity, we should devote more of our resources to finding ways of dealing with the problem.

Few, if any, sophisticated statistical studies of the physiological aspects of water quality have ever been made. Studies to find significant differences in general health and in degenerative and other diseases between different communities and population groups could shed light on the effects of differences in water quality and on the factors accounting for these differences. They could also point to more fundamental scientific studies deserving of emphasis in this hitherto largely ignored area of public health.