chapter 17

The freshwater we drink is a valuable resource that cycles in the biosphere.
- • Most of the water on Earth are saline ocean water; drinkable freshwater make up only 3% of all water.
  Out of that 3%, only 1% is easily reachable surface water, 87% is tied up in ice caps and glaciers.
- • The World Health Organization (WHO) estimates 2 billion people (about 1/3 of the world population) lack access to clean water.
  An additional 2.6 billion have no access to sanitation.
- • Water cycle
  Water falls to earth by condensation and precipitation, and cycles back by evaporation and transpiration (loss of water from leaves of plants).
  Review:
Reducing our water footprint involves making choices about our consumption patterns and using smart technologies.
- • Water footprint
  Developed countries tend to have a large water footprint (water use per capita).
  Canada has the largest water footprint.
- • Agriculture is the largest sector in water consumption.
  Reducing our water footprint involves choices such as
  - Avoiding bottled water - it takes 2.5 gallons of water to make one plastic bottle.
  - Avoiding foods that use more water.
- • Animals are consumers high on the trophic pyramid, while plants are producers.
  Thus animal food tend to be more water-intensive to produce than plant-based food.
  Beef requires the most water to produce per pound, while potato requires the least.
  
  Reducing our demand for products ranging from jeans to paper can also reduce our water footprint.
- • The top 4 U.S. household water use include toilet, washing machine, showering, and faucets.
  Technologies and behavior changes can reduce our water use.
  Reducing energy use also reduces water use, since it requires water to produce energy.
The water cycle replenishes our groundwater slowly; conservation efforts should include preserving natural resources such as wetlands.
- • In the natural water cycle, precipitation that falls on Earth can infiltrate the ground as a source of freshwater.
  Over time, groundwater accumulates within aquifers of porous rock layers.
  Impermeable man-made surfaces such as concrete reduce infiltration, and many aquifers suffer fast rates of withdrawal for human use.
  Depleted aquifers can lead to dry wells and saltwater intrusion in coastal areas.
- • Wetlands can conserve freshwater.
  - They can filter sewage and turn wastewater into freshwater.
  - They slow the flow of surface water, allowing it to recharge aquifers
  This re-constructed wetland in Arcata, CA also provides habitat for wildlife.