What do you use water for?
Drinking, of course. Bathing, naturally. But what else? Growing food, producing goods, recreation, maintaining healthy ecosystems: all require lots and lots of water.
Humans use six times as much water today as they did 100 years ago. People living in developed countries use a far greater proportion of the world’s water than people in less developed countries. What do people use all of that water for?
Human Uses of Water
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. 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. Can you name some examples of consumptive 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 (artifically adding water to the land or soil).
Three popular irrigation methods are:
- Overhead sprinklers.
- Trench irrigation: canals carry water from a water source to the fields.
- Flood irrigation (surface irrigation): fields are flooded with water and gravity distributes the water.
All 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. Water that runs off a field often takes valuable soil with it.
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.
Drip irrigation delivers water to the base of each plant so little is lost to evaporation and runoff.
Why Not Change?
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 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. Farmed fish are becoming increasingly common in grocery stores all over the world.
Workers at a fish farm harvest fish they will sell to stores.
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. 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.
Shrimp farms on the coast of Ecuador are shown as blue rectangles. Mangrove forests, salt flats, and salt marshes have been converted to shrimp farms.
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.
While industrialization is an essential feature of economic growth in developing countries, industrial practices may also produce negative environmental health consequences through the release of air and water pollutants and the disposal of hazardous wastes. This is often the case in developing countries, where less attention is paid to environmental protection, environmental standards are often inappropriate or not effectively implemented, and pollution control techniques are not yet fully developed.
Some industries have also started to use water for hydro power generation which is an alternative method for creating electricity. Hydro power is generated by using electricity generators to extract energy from moving water. Historically people used the power of rivers for agriculture and wheat grinding. Today, rivers and streams are re-directed through hydro generators to produce energy. According to the Department of Energy’s statistical body, the Energy Information Administration, hydropower accounted for 7% of U.S. electric generation in 2009, representing 65.9% of renewable generation that year.
Think about all the ways you use water in a day. 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?
People love water for swimming, fishing, boating, river rafting, and other activates. 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.
This National Geographic video chronicles the conflict between conserving the Yangtze River for recreational uses versus damming it for the clean energy China needs so badly: http://video.nationalgeographic.com/video/player/environment/energy-environment/energy-conservation.html.
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 an even smaller percentage of water use than recreational uses. A shortage of this water is a leading cause of global biodiversity loss.
Wetlands and other environments depend on clean water to survive.
Primary wastewater treatment involves the physical separation of suspended solids from the wastewater flow using primary clarifiers. This separation reduces total suspended solids as well as the biological oxygen demand (BOD) levels and prepares the waste stream for the next step in the wastewater treatment process.
Secondary wastewater treatment is the second stage of wastewater treatment that takes place after the primary treatment process. The process consists of removing or reducing contaminants or growths that are left in the wastewater from the primary treatment process. Usually biological treatment is used to treat wastewater in this step because it is the most effective type of treatment on bacteria, or contaminant, growth.
Tertiary is the next wastewater treatment process after secondary treatment. This step removes stubborn contaminants that secondary treatment was not able to clean up. Wastewater effluent becomes even cleaner in this treatment process through the use of stronger and more advanced treatment systems.
- Consumptive water use takes water out of the ecosystem; non-consumptive water use includes water that can be recycled and reused.
- People can use less water by having efficient systems for water use and by reusing and recycling water where possible.
- Some water must remain in the environment for recreational use for humans and to support ecosystems.
Use these resources to answer the questions that follow.
1. How much water is used in an average bath?
2. How much water is used in a 10 minute shower?
3. How much water is used to flush the toilet?
4. What is the water distribution for your state?
5. How much water does it take to produce bread?
6. How much water does it take to make a hamburger?
1. Why do people use so much more water than they used to?
2. Why don't localities and people use water in the most efficient way, rather than sometimes in wasteful ways?
3. What is aquaculture and why is it going to be increasingly important in the future?