Global Water Supplies
The planet contains an essentially constant quantity of water, 1.45 trillion cubic kilometers of it! Though it is used over and over again, changes form, passes through human bodies, through animals, through plants, through the soil, through the atmosphere, it never really goes away or leaves our biosphere. The water is literally recycled naturally in a process called the hydrologic cycle. Open water evaporation, mostly from the oceans, creates moisture content in the atmosphere. It condenses as it cools and falls back to the earth as rain or snow. When it reaches the earth, it flows downhill, in rivers and streams, seeps into the ground, is dipped into by all living things, and returns to the ocean, to be evaporated again into the atmosphere. Ideal water management involves humans learning to take part in the water cycle with the least interference. This focuses primarly on our management of waste water. Whatever we put in our water systems invariably gets cycled through the atmosphere and the food chain right back to us.
The oceans contain 97 percent of the water on the planet, but it is too saline for drinking or agriculture. It is desalinated in the process of evaporation off the ocean surface and enters into the water cycle as rain or snow. Only about one percent of the planet's fresh water resides in rivers and lakes. Most of our fresh water, some sixty-nine percent, is stored in snowpack, glaciers, or polar ice and is only partially available for use. The remaining thirty percent of Earth's fresh water exists as ground water, primarily in aquifers. Most of the fresh water that we use comes from the rivers as runoff or through pumping groundwater.
All of us use water everyday. Clean water is necessary for the aquatic life in our rivers and lakes, our cooking, our washing, and quenching our thirst. As a city grows and the population density increases, the demand for water increases not proportionately, but exponentially. This occurs not just through household or industrial use, but through the need to develop marginal land into cropland. To grow one ton of grain requires 1000 tons of water.
Global warming and human population increases are likely to make clean water the most critical natural resource on the planet. Recent appraisals by the United Nations Food and Agriculture Organization predict that "by the year 2025" overall water requirements, industrial, household, and agricultural, "appear to over commit all accessible runoff by some 5 percent."1 This compounds the problem of world food production because irrigation along with heavy fertilization is necessary to increase land productivity in pace with population growth. As Gary Gardner of the Worldwatch Institute wrote in 1997, "Globally water is in great excess, but because of operational limits and pollution, it can in fact support at most one more doubling of demand, which will occur in 20 to 30 years."2 That was ten years ago.
Water is absolutely essential to agriculture. Currently the industrial style of agriculture is water intensive. When we add large amounts of fertilizer to the soil, it must also be flushed with large quantities of water. This technique of using large amounts of fertilizer and water to grow all variety of edible grains, fruits, and vegetables can multiply a field's production many fold. Land that would otherwise be marginal crop land or worse can be productively cultivated through irrigation, either by diversion of water through dams and canals or groundwater (aquifer) pumping. Irrigated fields can be anywhere from three to ten times more productive than rain-fed. Huge crops have been harvested in areas that were historically little more than desert. Currently 36 percent of all crops and 50 percent of all grain production in the world are generated on irrigated land. 3 Seventy percent of all world water abstraction is for irrigation.4 While efficient water capture and usage is an absolute necessity for food production, both dam building, groundwater pumping, and irrigation offer an array of environmental trade-offs, further complicating increased food production.
When a river is engineered to do work, whether for a hydroelectric dam, flood control, or the facilitation of irrigation, it is at the expense of the health of that river. There is a corruption of the natural flow. Its path is changed from one of least resistance to one of maximized resistance. With that comes a cost beyond that of dam or canal construction. It is the cost of entropy added to the system, witnessed as environmental degradation. Fish habitats are disrupted. Temperature gradients in the water are altered. The flow of river sediments is obstructed. The long-term ecological stability of the watershed is stressed and altered.
The roundly hailed economic successes of damming the Columbia and the Colorado Rivers in the 1930s are now potential disasters. In the case of the Columbia, the salmon stocks, once a major fishing industry, have steadily dwindled to the point that the industry is all but gone. The Colorado is so heavily diverted by dams and irrigation canals it runs dry before reaching the sea. Dan Beard, while Commissioner of the U.S. Bureau of Reclamation in the early 1990s, stated "it is a serious mistake for any region in the world to use what we did on the Colorado and Columbia Rivers as examples to be duplicated."5 And yet building dams is exactly how many developing countries will seek to meet their agricultural and energy needs.
To further compound the matter, irrigation in itself is hard on the soil. Not only does the flush of water accelerate erosion, but, as evaporating water percolates through saturated ground, it leaches salts from the fertilizers to the surface, eventually leading to a sterilizing salinization of the topsoil. Current estimates say twenty percent of the world's irrigated land suffers from high levels of salinization, waterlogging, excessive erosion, and infertility.6 When increased fertilizer, herbicide, and pesticide concentrations are factored into the equation, the water draining back to the river is polluted with chemical toxins, further altering the river habitat. Downstream, where the river empties into the ocean, increased nitrogen levels rob waters of oxygen. "The North, Baltic, Arabian, and Black seas, the Chesapeake Bay, the Bay of Bengal, and the Pacific coasts of North and South America all suffer from periodic fish kills or the complete collapse of fisheries caused by nutrient overload."7 Agricultural runoff from the Mississippi Delta has created a dead zone in the Gulf of Mexico the size of New Jersey that has virtually killed all bottom-dwelling marine organisms. 8 Intensified techniques can bring productive farming to otherwise unusable land, but there are huge tradeoffs that gradually come to bear as we confront real biological limits.
As damming rivers is invariably a compromise to the natural water cycle, the pumping of ancient aquifers or groundwater to irrigate dry land for agricultural use also stresses the biosphere's delicate hydrological balance. These vast underground reserves are the sources of our purest water. In an effort to increase farming yield now, however, this ground water is often pumped faster than it can be naturally replenished, a borrowing from the future to meet today's needs. This is happening at dangerous rates in the United States, China, India, Mexico, and the Middle East. In fact, water tables are falling on every continent in the world.9
In the United States, ground water is currently being drawn out 25 percent faster than it can be replenished.10 The Ogallala aquifer beneath the American Great Plains that supplies water for some twenty percent of all irrigated land in the United States is now showing signs of depletion. It is all but empty at its shallow end in the Texas panhandle where pumping and irrigation has been forced to a halt.11 Ultimately, this depletion of ground water leads to a variety of other environmental losses. Land subsidence, intrusion of salt water into coastal areas, ground water contamination, and desiccation of nearby lakes are all further debits of unsustainable water use. In the overall scheme for feeding future generations, the cost of water will be a sure measure of the severity of the situation.
Throughout the course of human civilization running water has been used as a primary method of moving wastes of all kinds. While the natural processes of evaporation and filtration through the soil does remove toxins from the water, available runoff and other fresh water sources can no longer be used for the indiscriminate dumping of waste. Just like the forests or the soil, it is a critical and vital resource to manage. Though there is really no shortage of water itself, there is only so much fresh water available for use at any given time in any give place. As the planet's population increases and the climate warms, individual needs, agricultural needs, and industrial needs will increase exponentially. Water stresses, one of the reasons for current problems in Darfur and Sudan, will lead to armed conflict or mass human migration. Three options, in various combinations, are likely. Either we create more fresh water by energy dependent desalination, which creates yet another set of critical environmental tradeoffs, we relocalize communities to optimize water management, or we commit to decreasing human population.