Chapter 21: How We Obtain and Use Water

Water

• To understand water, we must understand its characteristics, and roles:– Water has a high capacity to absorb and store heat.

– Water is the universal solvent.

– Water has a high surface tension.

– Water is the only compound whose solid form is lighter than its liquid form.

– Sunlight penetrates water to variable depths, permitting photosynthetic organisms to live below the surface.

A Brief Global Perspective

• We are facing a growing global water shortage linked to the food supply.

• Global hydrologic cycle– Transfers water from the atmosphere, to land,

to oceans and back to atmosphere– 97% in oceans– 2% in ice– Only 0.001% in atmosphere

Interactions Between Surface Water and Groundwater

• Should be considered part of the same resource.

• Nearly all surface water environments have linkages w/ ground water– E.g. withdrawal of groundwater can lower

stream flow or lake levels– Pollution can spread from one source to the

other

Desalination as a Water Source

• Seawater is 3.5% salt• Desalination- a technology to remove salt

from water– Must be reduced to 0.05% to be fresh water– Requires large amount of energy, tied to fuel

prices– Has place value- price increases quickly with

transport distance– Discharge may affect local salinity

Some Trends in Water Use

• Trends in freshwater withdrawals by water-use categories suggests that:– 1. The major uses of water are for irrigation and

the thermoelectric industry.– 2. Water use for irrigation increased from 1950-

1980. It decreased and leveled off from 1985-2000

• due to better irrigation efficiency, crop type and higher energy costs.

Water Conservation

• The careful use and protection of water resources– Involves the quantity of water used and the

quality– Important component of sustainable water use– Expected that a number of innovations

(development of new customers value through solutions that meet new needs), will reduce the total withdrawals

Sustainability and Water Management

• From a water supply use and management perspective, sustainable water use defined as:– use of water resources by people in a way that

allows society to develop and flourish into an indefinite future

– W/o degrading the various components of the hydrologic cycle or the ecological systems that depend on it.

Sustainable Water Use

• General criteria:– Develop water resources in sufficient volume to

maintain human health and well-being.– Provide sufficient water resources to guarantee

the health and maintenance of ecosystems.– Ensure minimum standards of water quality for

the various users of water resources.

Sustainable Water Use

– Ensure that actions of humans do not damage or reduce long-term renewability of water resources.

– Promote the use of water-efficient technology and practice.

– Gradually eliminate water pricing policies that subsidize the inefficient use of water.

Groundwater Sustainability

• Sustainability involves a long term perspective– For groundwater even longer– Effects of pumping might not be seen

immediately– Long-term approach involves balancing

withdrawal with recharge

Water Management

• Management of water resources is a complex issue that will become more difficult as demand for water increases in the coming years.– Especially in areas like the Southwestern US

and other semi arid regions

Water Management

• Options for minimizing potential problems:– Alternating water supplies and managing

existing supplies better– Towing icebergs– As price goes up many innovative programs are

possible.

A Master Plan for Water Management

• New management philosophy is that surface water and groundwater are both subject to natural flux with time. – In wet years, there is plenty of surface water,

and the near-surface groundwater resources are replenished.

– During dry years, specific plans to supply water on an emergency basis must be in place and ready to use.

A Master Plan for Water Management

• Advanced planning may include– Drilling to wells that are presently isolated– Reuse of waste water– Develop surface water and use groundwater in

dry years– In wet years pump excess surface water

underground to recharge groundwater

Dams and the Environment

• Dams and their accompanying reservoirs generally are designed to be multifunctional structures. – Used for recreational activities – Generating electricity – Providing flood control– Ensuring a more stable water supply

• Often difficult to reconcile various uses at a given site.

Global Water Shortage Linked to Food Supply

• As human population grows there is growing concern that there won’t be sufficient water to grow the food to feed 8-9 billion people.– Food shortage linked to water resources a real

possibility. – Water also linked to energy (fuel to pump) as

energy cost goes up so does cost of food.

Global Water Shortage Linked to Food Supply

• Solution– Control human population growth– Conserve and sustain water resources– Need to be proactive now before significant

food shortages develop.