After completing this chapter you should be able to...
- Describe the different water reservoirs and identify which of these reservoirs are accessible to humans.
- Diagram the water cycle and explain how humans interact with the water cycle.
- Explain how groundwater is acquired from aquifers and how aquifers are recharged.
- Identify the main water-consuming sectors and their relative contributions to water usage.
- Compare physical and economic water scarcity.
- Outline strategies for addressing water shortages.
- Provide examples of water conserving technologies and behaviors.
Water is stored in water reservoirs. Although there is much water on Earth, only a fraction of this is freshwater that is accessible to humans. The water cycle describes the movement of water through each reservoir and involves sublimination and evapotranspiration, condensation, precipitation, infiltration, and surface runoff. Humans alter the water cycle through land use and diverting water flow. Precipitation—a major control of fresh water availability—is unevenly distributed around the globe. More precipitation falls near the equator, and landmasses there are characterized by a tropical rainforest climate. Less precipitation tends to fall near 30 degrees latitude, where the world’s largest deserts are located. Surface waters, including lakes are rivers, are an important source of freshwater. Additionally, groundwater can be extracted from aquifers. Agriculture is the greatest consumer of water, followed by industry and municipal use.
The water crisis refers to a global situation where people in many areas lack access to sufficient water or clean water or both. Physical water scarcity occurs when water resources are insufficient, but people face economic water scarcity when they cannot afford access to water. Partial solutions to the water crisis include dams and reservoirs, rainwater harvesting, aqueducts, desalination, water reuse, and water conservation.