Water Pollution

Some manufacturers are heavy users of water. For example, a large amount of electricity is needed to separate pure aluminum from bauxite so aluminum producers often locate near sources of hydroelectric power. Alcoa, the world’s largest aluminum producer, owns dams in North Carolina and Tennessee.

Water serves many other human purposes. People must drink water to survive. It is used for cooking and bathing. Water provides a location for boating, swimming, fishing, and other recreational activities. It is home to fish and other aquatic life. Water is used for most economic activities, including agriculture and services as well as manufacturing.

These uses depend on fresh, clean, unpolluted water. But that is not always available because people also use water for purposes that pollute it. Pollution is widespread because it is easy to dump waste into a river and let the water carry it downstream, where it becomes someone else’s problem. Water can decompose some waste without adversely impacting other activities, but the volume of waste often exceeds the capacity that many rivers and lakes can accommodate.

Demand for Water

Humans use around 9 billion cubic meters of water per year, or around 1,400 cubic meters per capita. The heaviest demand is for agriculture, followed by industry and municipal sewage systems (Figure 11-63). Water usage is either nonconsumptive or consumptive:

• Nonconsumptive water usage is use of water that is returned to nature as a liquid. Most industrial and municipal uses of water are nonconsumptive because the wastewater is primarily discharged into lakes and streams.

• Consumptive water usage is use of water that evaporates rather than being returned to nature as a liquid. Most agricultural uses are consumptive because the water is used primarily to supply plants that transpire it and therefore cannot be treated and reused.

Uses That Demand Water

China, India, and the United States use more than 1 billion cubic meters each. The United States has the world’s highest per capita consumption of water, at 2,800 cubic meters per person per year, or twice the worldwide average. Water usage is extremely high in the United States primarily because of agriculture. U.S. farmers raise a large number of animals to meet the high demand for meat that the average American consumes, as discussed in Chapter 9. These animals drink a lot of water in their lifetimes. A large amount of water is also needed in U.S. agriculture to irrigate fields of crops.

Per Capita Water Withdrawal by Region, 2010

Impact on Aquatic Life

Polluted water can harm aquatic life. Aquatic plants and animals consume oxygen, and so does the decomposing organic waste that humans dump in the water. Biochemical oxygen demand (BOD) is the amount of oxygen required by aquatic bacteria to decompose a given load of organic waste.

If too much waste is discharged into water, the water becomes oxygen starved and fish die. This can occur when bodies of water become loaded with municipal sewage or industrial waste. The sewage and industrial pollutants consume so much oxygen that the water can become unlivable for normal plants and animals, creating a “dead” stream or lake.

Similarly, when runoff carries fertilizer from farm fields into streams or lakes, the fertilizer nourishes excessive aquatic plant production—a “pond scum” of algae—that consumes too much oxygen. Either type of pollution reduces the normal oxygen level, threatening aquatic plants and animals.

Scientists have recently identified a source of pollution that increasingly affects aquatic life: small pieces of discarded plastic that enter the food chain and are difficult to remove from the human water supply.

Point-source Pollution

The sources of pollution can be divided into point sources and nonpoint sources. Point-source pollution enters a body of water at a specific location, whereas nonpoint-source pollution comes from a large, diffuse area. Point-source pollutants are usually smaller in quantity and much easier to control than nonpoint-source pollutants.

Point-source water pollution originates from a specific point, such as a pipe from a wastewater treatment plant. The two main point sources of water pollution are manufacturers and municipal treatment plants. Many factories use water for cooling and then discharge the warm water back into the river or lake. Fish adapted to cold water, such as salmon and trout, might not be able to survive in the warmer water. Steel, chemicals, paper products, and food processing are major industrial polluters of water.

In developed countries, sewers carry wastewater from sinks, bathtubs, and toilets to a municipal treatment plant, where most—but not all—of the pollutants are removed. The treated wastewater is then typically dumped back into a river or lake. Since passage of the U.S. Clean Water Act and equivalent laws in other developed countries, most treatment plants meet high water-quality standards.

In developing countries, sewer systems are rare, and wastewater usually drains, untreated, into rivers and lakes. The drinking water, usually removed from the same rivers, may be inadequately treated as well. The combination of untreated water and poor sanitation makes drinking water deadly in developing countries. Waterborne diseases such as cholera, typhoid, and dysentery are major causes of death.

Pause & Reflect 11.3.2

How might a change in the sources of energy used in factories help improve water quality?

Nonpoint-source Pollution

Nonpoint sources usually pollute in greater quantities and are much harder to control than point sources of pollution. The principal nonpoint source is agriculture. Fertilizers and pesticides spread on fields to increase agricultural productivity are carried into rivers and lakes by irrigation systems or natural runoff. Expanded use of these products may help to avoid a global food crisis in the short term, but they destroy aquatic life by polluting rivers and lakes. One of the world’s most extreme instances of nonpoint water pollution is the Aral Sea in the former Soviet Union, now divided between the countries of Kazakhstan and Uzbekistan.

Sustainability & Our Environment

The Shrinking Aral Sea

The The Aral Sea, located in Kazakhstan and Uzbekistan, was once the world’s fourth-largest lake.

Google see what has happened to the Aral Sea, and why it has happened.

Search for NASA World of Change: Shrinking Aral Sea. Or go to the home page of earthobservatory.nasa.gov and search for Shrinking Aral Sea.

1. According to NASA, what was the cause of the shrinking of the Aral Sea beginning in the 1960s?

2. What was the reason that the government made changes to the Aral Sea?

3. What has happened to the Aral Sea as a result of the changes?

4. What is the government trying to do the counteract the changes?

5. why has the color of much of the land near the lake changed from brown to white?

Aral Sea (a) 1990, (b) 2000, (c) 2015.