10. Water Resources and Water Pollution

• Core Case Study: The Colorado River


  – Overuse of the Colorado River challenges state/federal agencies and the people who live in these regions.

  
  

  – Increasing population and economic development place increasing demands on this limited supply of surface water.
• Will We Have Enough Usable Water?

  • By extracting water faster than nature can replace it, by wasting, polluting, and underpricing this natural resource, we are using available fresh water unsustainably
• Freshwater is not evenly distributed over the earth’s surface 


  – estimates show that one in nine people do not have access to clean, fresh water.
• Fresh Water is Available But It Is Not Distributed Evenly or Managed Properly.
• Globally, we have plenty of fresh water (recycled and purified by the hydrologic cycle), but pollute and overuse it faster than natural processes can replenish it.


  – A global economic and health issue

  – A security issue due to terrorism

  – An environmental issue as it determines and moderates the climate, and dilutes and removes pollutants and waste
• Groundwater infiltrates downward through spaces in soil and rocks.
• Zone of Saturation


  – underground areas of soil/rock where freshwater fills spaces between particles.
• Water Table


  – the top of the groundwater zone; fluctuates up and down depending on weather, and removal/replenishment rates.
• Aquifer


  – underground body of rock that absorbs and holds flowing water.
• Surface water


  : is the fresh water from rain and melted snow stored at the surface.
• Annually, 34% of the world’s reliable surface runoff is used


  • 70% goes to irrigate crops and raise livestock, 20% is used by industry, and 10% is used by cities for drinking, cooking, etc.
• Indirect and Virtual Water


  : water used to produce food and other products

  – this is a large part of our water footprint
• Water scarcity


  • is caused by dry climate, drought, overuse/inefficient use, and using water faster than it can be replenished
• Freshwater Scarcity Stress


  : a calculation that compares fresh water availability with the amount used by humans.
• In 263 of the world’s water basins, two or more countries share the available freshwater supplies


  – not always amicably
• How Can We Increase Freshwater Supplies?

  • Groundwater for food production and use by cities is being pumped from aquifers faster than it can be replenished by nature

  • Although dam-and-reservoir systems and water transfer projects expand water distribution, they also disrupt ecosystems and displace people

  • Freshwater supplies can be augmented by desalination of ocean water (expensive)
• Groundwater/Aquifer Usage Exceeds Replenishment Rate
• Overpumping limits food production, raises food prices, and widens the gap between the rich and the poor


  • As water tables drop, water must be pumped from lower depths (more energy and money)

  
  

  • Can cause land subsidence and sinkhole development where land above aquifers collapses

  – making recharge impossible

  
  

  • Can draw saltwater into freshwater aquifers

  – making it undrinkable/unusable for irrigation
• ADVANTAGE:

  
  

  Dams/reservoir systems capture and store surface runoff from a river’s watershed.


  – Water is released as needed to control upstream flooding, generate electricity (hydropower), supply fresh/irrigation water and provide recreational opportunities.
• ADVANTAGE:

  
  

  Water transfer projects use dams, pumps, and aqueducts to transfer water from water rich to water poor regions.
• Disadvantages of Large Dams and Water Transfer Projects


  • Dam/reservoirs displace millions of people, flood productive lands, impair the ecosystem services of rivers, and have a useful life expectancy of only 50 years

  
  

  • Water transfer projects reduce a river’s flow and flushing action (leading to pollution), and threaten fisheries and artificially cheapen costs

  – leading to inefficient and wasteful water use
• How Can We Use Fresh Water More Sustainably?

  • By reducing wastage, raising prices, slowing population growth and protecting ecosystems that store water naturally, we can use available freshwater more sustainably.
• More than half the world’s freshwater supply is lost annually due to evaporation, and inefficient use (irrigation) – Why?


  – Government subsidies and underpricing

  – Lack of subsidies for efficient water use
• Switching to modern irrigation methods (drip, central pivot etc.) will help reduce irrigation water usage by 10%


  – enough to supply everyone through 2025.
• Gravity Flow


  – efficiency 60% and 80% with surge valves

  – Water usually comes from an aqueduct system or nearby river
• Drip Irrigation


  — efficiency 90% to 95%

  — Above or below ground pipes or tubes deliver water to individual plant roots.
• Center Pivot


  — efficiency 80% with low-pressure, and 90% to 95% with LEPA sprinkler

  — Water usually pumped underground and sprayed from mobile boom and sprinklers
• Ways To Further Reduce Irrigation Water Loss

  Solutions:

  
• Industries need to intensify efforts to recapture/purify/recycle the water they use.
• In U.S. homes, toilet flushing is the single largest use of domestic freshwater.


  – Install low-flow toilets / showerheads / faucets

  – Fix water leaks / use front-loading washers

  – Use gray water / drip / smart sprinkler systems on landscaping, or replace lawns with drought tolerant plants
• Ways To Reduce Freshwater Losses in Industries

  Solutions:

  
• Flushing away industrial/household waste with freshwater causes pollution and is unsustainable.
• Gray water and industrial waste water from sewage treatment plants can be used to clean equipment, flush away waste, water lawns, and irrigate non-food crops.
• You Can Reduce Your Use and Waste of Freshwater

  What Can You Do?

  
• How Can We Deal with Water Pollution?

  • Humans can use natural methods to treat sewage, cut resource use and waste, reduce poverty, and slow population growth to reduce water pollution

  – but the best way to reduce water pollution is to prevent it
• Water pollution


  : water quality changes that harm living organisms or make water unfit for drinking/ irrigation/recreation.
• Point sources


  : specific identifiable locations
• Non-point sources


  : diffuse areas

  • Difficult to identify/control, expensive to manage.
• The leading causes of water pollution are agriculture activity/industrial facilities/mining.
• Major Pollutants and Their Sources