Water crisis: inevitable or preventable?

Thursday, November 23, 1995

People everywhere are concerned about future water resources - and rightly so. Many surface sources are contaminated or over-used. Tales of groundwater contamination and lowering of water levels are common, and citizens feel threatened. But is the situation as bad as it looks?

Water supply depends on the hydrologic cycle, which is rather constant over decades. We can depend on about 30 inches of rain falling on the conterminous United States each year, of which about two-thirds is consumed by vegetation, and one-third is carried by rivers to the oceans. This constitutes an annual volume of nearly two million gallons of pure, distilled water per person. There will never be a real water shortage in the United States.

That simple fact becomes irrelevant because so many people want to live in large metropolitan areas or in deserts. City- and desert-dwellers demand enormous quantities of water to suit their lifestyles. Deserts provide two elements for profitable farming: rich soil and sunshine. The rest of the nation provides the last necessary ingredient: cheap water for irrigation.

To meet these demands, we manipulate the runoff portion of the hydrologic cycle by diverting surface water to cities, where little is consumed but all is degraded before being returned to the surface drainage to cities, where little is consumed but all is degraded before being returned to the surface drainage system. We also divert water for irrigation with the intent that this water be consumed - that is, converted to vapor by transpiration. Surplus water is degraded, and return water contaminates either the surface-water or groundwater reservoir.

Short-term variations in weather patterns lead to droughts. To meet this contingency, we store surface water behind dams or transfer water from one drainage basin to another. These measures ensure that the total supply will not change over the years; although excess water drains in a matter of days or weeks, while depleted reservoirs are replenished in months, sometimes years.

Excessive groundwater use, on the other hand, does deplete storage, especially in heavily pumped, productive aquifers. In the West, most groundwater for irrigation comes from the aquifers in the Central Valley of California, the alluvial aquifers of central Arizona, and the Ogallala aquifer in the southern High Plains region. Declining levels in wells were proof of exploitation.

Because surface water now has to be imported to California and Arizona, groundwater production has been curtailed; as a result, groundwater levels have recovered somewhat, alleviating the crisis for that particular region. There can be no such solution for the Ogallala aquifer, but that does not imply impending doom. As water levels drop in wells, pumping lifts and costs rise. When a farming enterprise is no longer profitable, irrigation stops. This point will always be reached long before the aquifer is totally depleted. The region will revert to dryland farming and grazing; and although the aquifer will remain a good water source for the community, the groundwater used for irrigation will be lost and irrecoverable.

California's chronic water shortages provide the best-known example for a regional water shortage. Most of the state's water is imported to benefit the user; 85 percent is used by farms for irrigation, 10 percent by municipalities, and 5 percent by industries. About half of the irrigation water comes from surface sources and half from groundwater.

To reduce water consumption, Los Angeles instituted regulations forbidding restaurants to serve drinking water, unless requested. Such steps are ineffective because consumption is small. No doubt, however, it raises public awareness. On the other hand, a 15 percent reduction in irrigation use would nearly double the amount of water available to cities and industries. Are we so uniquely naive as to think that only modest controls on irrigation water usage will solve California's water crisis?

Ninety-nine percent of our water supply could be of lesser quality without affecting our lifestyle. Over most of Earth, rain and snow provide enough water to satisfy human needs; this will remain the case as long as climatic changes are not severe. Most surface water is easily filtered and disinfected to make it potable. All but the most primitive societies have the technology and resources to assure enough water for household use by storing rain water and purifying surface water, or in extreme cases, melting snow or desalinizing brine.

Then, why all the fuss about future water supplies? Because we insist that all water be available to all users and be potable. Therein lies the key to our current distress and future relief.

The events leading to California's water shortages are common to hundreds of communities. Settlements developed near supplies of potable water, food, and shelter. Rivers, lakes, springs, and shallow groundwater served world populations until the turn of the 20th century.

Then, great population increases and new water needs overwhelmed traditional supply and delivery systems. We responded with more and bigger dams, and more wells to provide water for showers, toilets, dishwashers, clothes washers, and innumerable conveniences. We also subsidized industrial water costs. Today, when shortages occur, we build a pipeline to a more distant source.

Let's look at Mexico City, for example. The springs of the Valley of Mexico provided water for the Aztecs, Spanish colonists, and modern Mexico City until they dried up in the early 1930s because of heavy pumping from the local aquifer. Wells in the Valley of Mexico now provide almost all the city's municipal supply, producing about 43 cubic meters of water per second (about one billion gallons per day). But that's not enough for 20 million people. An additional 500 million gallons per day is imported, mostly from a surface reservoir 80 miles away, from which water is lifted 3,600 feet, treated, and piped to Mexico City.

The solution to the water crisis is not to find a new source, farther away. In most cases, the source doesn't exist - or if it does, it belongs to someone else. Even if water can be bought, it will provide only temporary relief if demand matches population growth.

What is the answer? First, control population growth. Second, make better use of the current water supply, and ensure its availability to future users by careful treatment of sewage and disposal of wastes. Third, use all reasonable means to protect our existing water resources so that we can continue to enjoy unlimited supplies of potable water. Finally, include just a little reason in our water-management strategies.

Robert N. Farvolden, UW Professor Emeritus. Reprinted from Geotimes (July 1995).