Water Information Center - Drinking Water Basics

Drinking Water Basics

Water Management: Managing a Critical Resource

From dealing with dwindling water supplies to monitoring contaminants in public drinking water, water management and regulation efforts involve nearly 20 federal agencies and thousands of regional, state, and city entities. As the nation's water challenges increase in complexity, more agencies and stakeholders may become involved. Protecting the safety and reliability of America's taps is a large and important challenge—and one that the general public does not understand very well.

Factors Affecting Water Supply

Precipitation levels vary widely across the United
States. Image courtesy of the U.S. National Atlas.Water may seem to be a stable resource in places where it appears whenever one turns on the tap. In reality, however, water supplies—especially those that depend on surface water—vary dramatically with the seasons, weather patterns, and long-term shifts in climate. Precipitation (rain, snow, sleet, hail, frost, and dew) produces much of the world's drinking water. But precipitation ranges from less than 4 inches per year to more than 160 inches per year in different regions of the United States.

Drought
So little rain fell in the midwestern United States in the 1930s that parched topsoil was literally carried away by the wind. The drought caused sun-blocking dust storms so severe that they were called "black blizzards" and contributed to the destruction of hundreds of millions of acres of previously fertile agricultural land. Spanning across

Severe drought in 2007 left what is
normally a pond outside Nicholasville,
KY, nothing but dry, cracked ground.
Image from the Lane Report; photo by
Andy Olsen.70 percent of the country and lasting nearly a decade in some places, the "Dust Bowl" drought compounded the effects of the Great Depression and led millions to flee the Midwest. It is considered to be one of the most catastrophic weather events in U.S. history.

Drought isn't limited to occasional catastrophic events or the famously dry American southwest. In the past five years alone, drought conditions have been recorded in nearly every region of the United States. Drought is a unique type of natural disaster in that it seldom has a spectacular or sudden onset. Damage inflicted by drought usually occurs subtly over a span of months to years instead of minutes to days. Unfortunately, few areas are immune to drought.

The key to adequate drought management lies in pre-drought preparation. measures that managers can take to protect against the effects of drought include, among others, increasing water storage, developing a good water system maintenance program, periodically evaluating emergency water sources, establishing a plan for managing water demands, and building public information programs. These points and others are explored in the National Research Council report Drought Management and Its Impact on Public Water Systems (1986).

Case Study in Competing Uses: The Columbia River Story
For thousands of years, Washington State's Columbia River salmon runs were among the most prolific on Earth. Unfortunately, dams and hydroelectric power plants, commercial fishing operations, logging, irrigated agriculture, and human population growth have altered the river's flows. As a result of degrading salmon habitat, some of the area's native salmon populations are now listed as threatened or endangered under the federal Endangered Species Act.

How can the Columbia River's resources be managed to serve both people and fish? State officials and others have faced difficult decisions as they struggle to satisfy competing demands from the federal government, environmental groups, cities and towns, farmers, and Native American tribes who rely on the river's water. The river continues to offer potential for economic development: according to one calculation, withdrawing a million acre-feet of water (about 0.5 percent of the river's annual flow) for irrigation would create 18,000 jobs and annual revenues of approximately $850 million. However, even a relatively small withdrawal of water could have a negative effect on the area's threatened and endangered salmon.

Ultimately, the state decided to focus its efforts on developing new ways to store the river's water and improve the efficiency of existing storage facilities. Under the state's plan, one of every three gallons of water made newly available through this process would be set aside for protection of the salmon.

Elements of the Columbia River story echo throughout watersheds across the country. Allocating water resources to satisfy competing demands often requires effective communication among stakeholders, thorough analysis of the watershed's hydrological conditions, and creative and innovative solutions. For more information on Columbia River water allocation, see the National Research Council report Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival (2004).

Climate Change
The Earth's climate is changing and its atmosphere is warming. What might this mean for freshwater resources?

Rising water demands. hotter summers mean thirstier people and plants. Temperature increases will likely contribute to higher water demands. In addition, more evaporation from reservoirs and irrigated farmland will lead to faster depletion of water supplies.
Increased drought. Scientific evidence suggests that rising temperatures in the southwestern United States will reduce river flows and contribute to an increased severity, frequency, and duration of droughts.
Seasonal supply reductions. Many utilities depend on winter snowpack to store water and then gradually release it through snowmelt during spring and summer. Warmer temperatures will accelerate snowmelt, causing the bulk of the runoff to occur earlier—before crops can use the water—and potentially increasing water storage needs in these areas.
Long-term water supply reductions. Many communities depend on seasonal water runoff from glaciers. Although shrinking glaciers create higher runoff (and thus more water) in the short term, the longer-term disappearance of glaciers threatens this important water resource.

Getting Every Last Drop

Residential uses of water in the united States
(typically 200 gallons per day per household).
(Click to enlarge) Data from Mayer, et al. Residential
End Uses of Water, 1999.Water is a finite resource, yet demands for it are rapidly increasing. The residents of Tucson, Arizona are well aware of this: Tucson receives just 12 inches of rain per year and sees an influx of thousands of new residents each month. To help preserve its dwindling groundwater supply, the city began implementing a series of water-conservation measures in the 1970s. These efforts, which included public education, improving infrastructure to reduce leakage, mandating water-conserving landscaping, and even employing "water cops" to crack down on water waste, have helped drop the city's per capita potable water use from 205 gallons per day in 1973 to 163 gallons per day today. That 42-gallon reduction is widely celebrated as a successful water conservation achievement. But expanding populations in Tucson and other cities continue to increase urban water demands, making conservation efforts essential components of water management.

Five Steps to Water Conservation
A variety of practices and technologies—from the low-tech to the high-tech—can help stretch limited water supplies. Here are just a few:

Improperly aimed sprinklers waste water
by allowing it to run off onto sidewalks and
into storm drains. Image courtesy of
City of Santa Cruz Water Department.

Drought-resistant plants reduce
the need for watering.
Reduce leaks. From the individual household faucet or toilet to municipal water distribution pipes, repairing or replacing leaking water infrastructure can save water— and money.

Install low-flow fixtures. Water-conserving toilets, showerheads, and faucets, which are now required by building code in many areas, can reduce domestic water use by 50 percent or more.

Change water-wasting habits at home. Small habit changes such as running the dishwasher or washing machine only for full loads or taking shorter showers can, over time, mean big water savings.

Use water-saving landscaping techniques. Some primary water-conserving landscaping techniques (also known as xeriscape landscape principles) include grouping plants with similar water needs together, limiting water-guzzling lawns, using drought-tolerant plants, and irrigating efficiently.

Irrigate crops more efficiently. Conserving the amount of water used to irrigate crops benefits everyone: farmers spend less money on water, and more water is available for other purposes. Advanced techniques can help farmers monitor the precise level of moisture in soil and alter their irrigation practices to limit overall water use. In an approach called deficit irrigation, for example, irrigation is reduced at noncritical times but crops are properly watered at critical flowering and fruiting stages.

Water Storage
Thinking about your local reservoir may conjure visions of water sports, fishing, or picnicking, but reservoirs serve a much more vital purpose. Reservoirs, or man-made lakes, are typically created by building dams across rivers (some also occur naturally). Reservoirs even out the fluctuations in a water supply by storing water when it is abundant and releasing it later, especially when a water supply diminishes during drought.

Water towers, a familiar sight along nearly every highway in America, help to make sure that water deliveries remain relatively constant even during peak water use times. Their main purpose, however, is to elevate the water level high enough to supply adequate water pressure throughout a distribution system.

As demand for water increases, so does the need for new reservoirs. But a number of factors—including high evaporation rates, damage to fish and ecosystems, and decreasing availability of land for dam construction—have made building additional dams less desirable. An alternative approach, managed underground storage, involves capturing water from a source, storing it in an underground aquifer, and then pumping it back up through wells for use.

Prospects for Managed Underground Storage of Recoverable Water

Managed underground storage systems do not require the requisition of large amounts of land that surface reservoirs do, and loss of water through evaporation is not a problem. Nevertheless, underground storage does pose some challenges. Among them are the generally high costs of design, construction, and monitoring, and the potential for contamination from chemical reactions between the water and aquifer materials. The National Research Council report Prospects for Managed Underground Storage of Recoverable Water (2008) explores the promise and challenges of this approach.

Water Recycling
Water recycling, also called water reuse or reclamation, can be either direct or indirect. In direct potable reuse, wastewater is used for drinking purposes directly after treatment. Direct potable reuse is not used for large-scale public water systems in the United States.

In indirect potable reuse, treated wastewater is discharged and mixed into a lake, a river, or groundwater before being extracted and treated again for use. Unlike direct potable reuse, indirect potable reuse is now fairly common, especially in the southwestern United States. For example, Orange County, California, recently completed a state-of-the-art water purification system to augment its drinking water supply with recycled wastewater, creating a virtually "drought-proof" water supply for millions of individuals. For more information on potable reuse of water, see the National Research Council report Issues in Potable Reuse: The Viability of Augmenting Drinking Water Supplies with Reclaimed Water (1998).

Recycled water is commonly used to irrigate parks and golf courses. Such recycling cuts down on the amount of high quality water extracted for non-potable purposes, thus helping to conserve the best freshwater resources for drinking.

Desalination
Another option for augmenting water supplies is a process called desalination. During desalination, salt and other dissolved solids are removed from seawater or brackish groundwater. The worldwide desalination capacity has approximately doubled since 1995: today, the world's operational desalination capacity is more than 10,000 million gallons per day. That capacity continues to grow steadily. Nearly half of the current global desalination capacity is located in the Middle East, with the remaining capacity distributed throughout North America, Europe, and Asia.

Total desalination capacity by country, 2006.
Copyright International Mapping Associates.Although their total combined capacity is estimated at about 0.01 percent of total U.S. water use, desalination plants have been built in every state in the United States. Nearly half of the plants are small facilities built for specific industrial needs. Florida, California, Texas, and Arizona currently have the greatest installed desalination capacity.

Until recently, the cost of desalination was prohibitively expensive in many areas. Advances in membranes and reverse-osmosis technologies, however, have significantly reduced the costs of producing desalinated water. Meanwhile, the costs of other alternatives for augmenting water supplies have continued to rise, making desalination more attractive in a relative sense. For further discussion of the current and future status of desalination technologies, see the National Research Council report Desalination: A National Perspective (2008).

Like many other water management options, desalination has potential environmental implications that need careful consideration. For example, seawater intake mechanisms can harm marine life, and energy use by desalination plants can mean increased greenhouse gas emissions. One of the biggest concerns is the ecological impact of discharging the salt concentrates that are produced in the desalination process. Yet the cost of discharging salt concentrates in an environmentally sustainable manner can be prohibitively expensive where low-cost waste management options are not available.

Case Study: New Science to Inform Water Management in the Southwest
The Colorado River provides water for tens of millions of people from San Diego, California, to Denver, Colorado. Although gauges have continuously monitored the river's flow for more than a hundred years, scientists didn't know until recently how recorded flows compared with the river's longer-term history.

Image courtesy of
Connie Woodhouse.Using tree-ring analysis, scientists are now able to estimate Colorado River flows dating back to the 15th century. These estimates show that extended droughts are an integral part of the basinss climate and suggest that stream-flow measurements over the past 100 years may offer an overly optimistic forecast of future water availability. Given the severity of the droughts indicated by the reconstructed river history, future droughts may be even worse than those of the past century.

Analyses have revealed that the Colorado River Compact of 1922, which governs water allocations between the upper and lower Colorado River basins, was based on a short record of relatively high flows. This means that the water allocations already exceed the mean annual flows in the Colorado River; any future decreases in the river's flow would make the situation even more serious for the region's water users. The National Research Council report Colorado River Basin Water Management (2007) takes an in-depth look at water issues in the Colorado River Basin.