Learning Objectives

• Discuss how much water is taken up by each water use.
• Explain the difference between consumptive and non-consumptive water uses.
• What is the origin of California’s fresh water supply?

Vocabulary

• aquaculture
• consumptive water use
• drip irrigation
• non-consumptive water use

Introduction

What is the most important thing for all life on Earth? Arguably, it is water (arguably, because a lot of other things are needed for life, too). From the smallest bacteria to the largest trees, all forms of life on Earth depend on water for survival. Although you could likely go a few weeks without eating, people cannot survive for more than a few days without drinking water.

Human Uses of Water

Besides drinking and washing, people need water for agriculture, industry, household uses, and recreation (Figure below). Recreational use and environmental use average 1% each.

Water use can be consumptive or non-consumptive, depending on whether the water is lost to the ecosystem.

• Non-consumptive water use includes water that can be recycled and reused (Figure below). For example, the water that goes down the drain and enters the sewer system is purified and then redistributed for reuse. By recycling water, the overall water consumption is reduced.

• Consumptive water use takes the water out of the ecosystem (Figure below). Can you name some examples of consumptive water use?

Agricultural Water Use

Some of the world’s farmers still farm without irrigation by choosing crops that match the amount of rain that falls in their area. But some years are wet and others are dry. For farmers to avoid years in which they produce little or no food, many of the world’s crops are produced using irrigation.

Two popular irrigation methods are:

• Overhead sprinklers (pictured in the Figure above).
• Trench irrigation: canals carry water from a water source to the fields.

Both of these methods waste water. Between 15% and 36% percent of the water never reaches the crops because it evaporates or leaves the fields as runoff (Figure below). Water that runs off a field often takes valuable soil with it. So why do people use these methods?

A much more efficient way to water crops is drip irrigation (Figure below). With drip irrigation, pipes and tubes deliver small amounts of water directly to the soil at the roots of each plant or tree. The water is not sprayed into the air or over the ground so nearly all of it goes directly into the soil and plant roots.

So back to the question, why do farmers use wasteful irrigation methods when water-efficient methods are available? Many farmers and farming corporations have not switched to more efficient irrigation methods for two reasons:

1. Drip irrigation and other more efficient irrigation methods are more expensive than sprinklers, trenches, and flooding

2. In the United States and some other countries, the government pays for much of the cost of the water that is used for agriculture. Because farmers do not pay the full cost of their water use, they do not have any financial incentive to use less water.

What ideas can you come up with to encourage farmers to use more efficient irrigation systems?

Aquaculture

Aquaculture is a different type of agriculture. Aquaculture is farming to raise fish, shellfish, algae, or aquatic plants (Figure below). As the supplies of fish from lakes, rivers, and the oceans dwindle, people are getting more fish from aquaculture. Raising fish increases our food resources and is especially valuable where protein sources are limited.

Growing fish in a large scale requires that the fish stocks are healthy and protected from predators. The species raised must be hearty, inexpensive to feed, and able to reproduce in captivity (Figure below). Wastes must be flushed out to keep animals healthy. Raising shellfish at farms can also be successful.

For some species, aquaculture is very successful and environmental harm is minimal. But for other species, aquaculture can cause problems. Natural landscapes, such as mangroves, which are rich ecosystems and also protect coastlines from storm damage, may be lost to fish farms (Figure below). For fish farmers, keeping costs down may be a problem since coastal land may be expensive and labor costs may be high. Large predatory fish at the 4th or 5th trophic level must eat a lot, so feeding large numbers of these fish is expensive and environmentally costly. Farmed fish are genetically different from wild stocks and if they escape into the wild they may cause problems for native fish. Because the organisms live so close together, parasites are common and may also escape into the wild.

Industrial Water Use

Industrial water use accounts for an estimated 15% of worldwide water use with a much greater percentage in developed nations. Industrial uses of water include power plants that use water to cool their equipment, and oil refineries that use water for chemical processes. Manufacturing is also water intensive (Figure below).

Household Use

Think about all the ways you use water in a day (Figure below). You need to count the water you drink, cook with, bathe in, garden with, let run down the drain, or flush down the toilet. In developed countries, people use a lot of water while in less developed countries people use much less. Globally, household or personal water use is estimated to account for 15% of world-wide water use.

Some household water uses are non-consumptive, because water is recaptured in sewer systems, treated, and returned to surface water supplies for reuse. Many things can be done to lower water consumption at home.

• Convert lawns and gardens to drip-irrigation systems.
• Install low-flow shower heads and low-flow toilets.

In what other ways can you use less water at home?

Recreational Use

People love water for swimming, fishing, boating, river rafting, and other activities (Figure below). Even activities such as golf, where there may not be any standing water, require plenty of water to make the grass on the course green. Despite its value, the amount of water that most recreational activities use is low: less than 1% of all the water we use.

Many recreational water uses are non-consumptive including swimming, fishing, and boating. Golf courses are the biggest recreational water consumer since they require large amounts for irrigation, especially because many courses are located in warm, sunny, desert regions where water is scarce and evaporation is high.

Environmental Use

Environmental use of water includes creating wildlife habitat. Lakes are built to create places for fish and water birds (Figure below). Most environmental uses are non-consumptive and account for even a smaller percentage of water use than recreational uses.

California Water Resources

California has many sources of water (Figure below). The winter snow pack in the Sierra Nevada and other mountain ranges feeds rivers that crisscross the state. Virtually all of these rivers are dammed, some more than once, to supply power and water to the cities and farmlands of the state.

Groundwater is also an important source of water in California. In a normal year about 40% of the state’s water supply comes from groundwater. In a drought year, the number can rise to 60% or more. The largest groundwater reservoirs are found in the Central Valley where thousands of years of snow melt has fed the aquifers. In many locations, much more groundwater is used each year than is available to recharge the aquifer. Subsidence of the land is common in these regions.

Despite these vast water sources, the state’s large population and enormous agricultural landscape put a strain on the water supply. Water rights in California are complex and controversial. Although about 75% of the water resources are in the northern one-third of the state, the largest usage, about 80%, is in the southern two-thirds. Besides projects that exist to distribute water within the state, a large source of water is the Colorado River.

KQED: State of Thirst: California’s Water Future

California’s population is growing by hundreds of thousands of people a year, but much of the state receives as much annual rainfall as Morocco. With fish populations crashing, global warming, and the demands of the country’s largest agricultural industry, the pressures on our water supply are increasing. Learn more at: http://www.kqed.org/quest/television/state-of-thirst-californias-water-future

Lesson Summary

• Human water use is dominantly in five categories: agriculture, industry, domestic, recreation, and environmental.
• Water use can be consumptive or non-consumptive.
• Despite California’s abundant water supply from surface streams and groundwater, the state has a number of water rights issues that will be important long into the future.

Review Questions

1. List the three water uses that consume the most fresh water.

2. How do farmers grow crops when there is no irrigation?

3. Describe why some water uses are called consumptive.

4. Describe drip irrigation and why it wastes less water than irrigating with sprinklers.

5. Explain why water use by humans has increased dramatically in the past century or so.

6. Why do farmers sometimes use more wasteful methods of irrigation than are available?

7. What are some of the positives of aquaculture? Some of the negatives?

8. Describe four consequences of water shortages to people.

9. What is the origin of California’s fresh water sources?

10. Describe why droughts are more serious in the arid regions of the world than in wetter regions.

Points to Consider

• Is fresh water ever more valuable than gold or diamonds?
• How can farmers and other people be encouraged to use more efficient irrigation methods?
• With such abundant water resources, why do California’s planners worry about the state’s future water resources?