NRW105: 7.2 Water Supply: Resource Depletion

Water Supply Problems: Resource Depletion

• Groundwater pumping from wells leads to a localized drop in the water table, forming a cone of depression.
• Numerous wells pumping water for a long time can cause significant regional water table decline.
• Significant regional water table decline is known as groundwater mining, and requires drilling deeper and more expensive wells that tap into more saline groundwater.
• Overuse can deplete rivers, lakes, and artificial lakes (reservoirs).
• Glaciers are diminishing because of accelerated melting from global warming over the past century.
• Saltwater intrusion occurs when overpumping of freshwater aquifers near coastlines allows saltwater to contaminate freshwater zones.
• A cone of depression in an unconfined aquifer can alter regional groundwater flow, drawing pollution toward the pumping well.
• A drop in the water table can lead to subsidence (gradual sinking over a large area) and sinkholes (rapid sinking over a small area).

Water Supply Crisis

• Many areas lack access to sufficient or clean water, creating a global water crisis or water stress.
• Water stress is most severe in areas with low precipitation (deserts) and/or high population density.
• Global warming could worsen the water crisis by changing precipitation patterns and melting mountain glaciers.
• Melting glaciers can raise sea levels, increasing saltwater intrusion in coastal aquifers.
• A 2006 United Nations report stated 700 million people (11% of the world's population) lived with water stress with most living in the Middle East and North Africa.
• By 2025, over 3 billion people (about 40% of the world population) are projected to live in water-stressed areas, especially in China and India.
• The water crisis can impact food production and create global tensions and conflicts.
• Historic and future areas of water conflict:
  • Middle East: Euphrates and Tigris River among Turkey, Syria, and Iraq; Jordan River among Israel, Lebanon, Jordan, and Palestinian territories.
  • Africa: Nile River among Egypt, Ethiopia, and Sudan.
  • Central Asia: Aral Sea conflict among Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, and Kyrgyzstan.
  • South Asia: Ganges River conflict between India and Pakistan.

Sustainable Solutions to the Water Supply Crisis?

• Addressing the current and future water crisis involves using multiple approaches to expand freshwater supplies and promote sustainability.
• Traditional approaches include dams and aqueducts.
• Reservoirs created by dams in rivers can store water during wet periods for use in dry periods and for urban water supplies.
• Dams and reservoirs provide benefits like hydroelectricity, flood control, and recreation.
• Drawbacks of dams and reservoirs:
  • Water loss through evaporation, especially in dry climates.
  • Downstream river channel erosion.
  • Ecosystem impacts such as habitat change and interference with fish migration.
• Aqueducts transport water from areas of plenty to areas of need.
• Aqueducts can be controversial and politically challenging, particularly for long-distance transfers.
• Water diversion via aqueducts can lead to droughts in the source area.
• Owens Lake and Mono Lake in central California nearly disappeared after river flow was diverted to the Los Angeles aqueduct.
  • Owens Lake remains almost completely dry.
  • Mono Lake recovered significantly through legal intervention.

Desalination

• Desalination is process, removing dissolved salt from seawater or saline groundwater to created potable water.
• Desalination methods include boiling, filtration, and electrodialysis.
• Desalination can be very expensive and uses a lot of energy, making the water more expensive than conventional sources.
• Desalination produces highly saline wastewater, which must be disposed of, creating environmental concerns.
• Desalination is most common in the Middle East, where oil is abundant but water is scarce.

Conservation

• Conservation means using less water and using it more efficiently.
• Home water conservation includes:
  • Engineered features: high-efficiency clothes washers, low-flow showers and toilets.
  • Behavioral decisions: growing native vegetation, turning off the water while brushing teeth, and fixing leaks.
• Rainwater harvesting involves collecting and storing rainwater for reuse.
• Efficient irrigation is crucial in agriculture due to its large water demand.
• Water conservation strategies in agriculture:
  • Growing crops in areas with sufficient natural rainfall.
  • Drip irrigation systems to minimize evaporation.
  • No-till farming to reduce evaporative losses.
  • Reusing treated wastewater from sewage treatment plants.
  • Using recycled wastewater to recharge aquifers.