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
A Brief Global Perspective • At Earth’s surface water can be found in liquid, solid or gaseous form. • Residence time varies from a few days to thousands of years • Amount of water for which all people, animals and plants compete is < 1% • Industrial production increases water use • Mass of water used 1000x total production of minerals
Groundwater and Streams • Groundwater refers to the water below the water table • Where saturated conditions exist • Locations where surface waters move into the ground are recharge zones • Places where it flows or seeps out are discharge zones (points) • Area where water seeps through pore spaces known as vadose zone
Groundwater and Streams • Aquifer is an underground zone from which groundwater can be obtained • When water is pumped from an aquifer forms a cone of depression
Streams • Effluent stream • Flow is maintained during the dry season by seepage • Perennial stream • Influent stream • Entirely above the water table and flows only in direct response to precipitation • Ephemeral stream • A given stream can have reaches that are both or intermittent at varying times of year.
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
Water Supply: A US Example • Water supply at any point on the land surface depends on several factors in the hydrologic cycle, • including the rates of precipitation, evaporation, transpiration • stream flow • subsurface flow • Water budget • A model that balances the inputs, outputs, and storage of water in a system. • Precipitation - evaporation = runoff
Water Supply: A US Example • Amount of water vapor passing over the US every day ~ 152,000 million m3 • 10% falls as precipitation (66% of which is evaporated or transpired) • Only 34% enters surface or groundwater
In developing water budgets for water resources management it is useful to consider annual precipitation and runoff patterns. Potential problems can be predicted in areas where average runoff and precip low Total storage of runoff not possible because of evaporative losses Precipitation and Runoff Patterns
Droughts • Because there are large annual and regional variations in stream flow, even areas with high precipitation and runoff may suffer from droughts.
Groundwater Use and Problems • ½ the people in the US use groundwater as a primary source of drinking water • 20% of water used • In many parts of the country withdrawal from wells exceeds natural inflow • Overdraft • Nonrenewable resource • Problems include damage to river basins and land subsidence
Desalination as a Water Source • Seawater is 3.5% salt • Desalination- a technology to remove salt from water • Must be reduces 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
Water Use • Off-stream use • Refers to water removed from its source for use • May be returned to source after use • Or consumptive use- water enters tissues, product or evaporates during use and not returned
Water Use • In-stream use • The use of the river for navigation, hydroelectric power, fish and wildlife habitats, and recreation. • Multiple uses can create controversy
Water Use • Another problem with off stream use is how much water can be removed w/o damaging the stream ecosystem. • E.g. Aral Sea. Diverting water for agriculture caused sea to dry up • Surface area of sea reduces 90% in 50 years
Aral Sea • Salt content of the water has increased • Dust storms from dry salt flats • Climate changes • Winters colder, summers warmer • Loss of fishing and decline of tourism
Transport of Water • Ancient civilizations constructed canals and aqueducts to transport water • From distant river to where it is needed • In modern civilization water moved from areas of abundant rain and snow fall to areas of high usage • E.g. California moves water from north to south • E.g. New York City has had to obtain water from farther and farther away
Some Trends in Water Use • Withdrawal of surface water far exceeds withdrawal of groundwater • Since 1980 use has decreases and leveled off • Suggests improvement in water management and conservation
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.
Some Trends in Water Use • 3. Water use by thermoelectric industry decreased slightly in 1980, and stabilized in 1985. • Due to reticulating water for cooling • 4. Water for public and rural supplies continued to increase through the period from 1950 to 2000 • presumably related to the increase in human population.
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 innovations will reduce the total withdrawals
Agricultural Use • Improved irrigation could reduce agricultural withdrawals by 20 to 30% • Tremendous savings because ag is the biggest user
Agricultural Use • Suggestions for conservation: • Price agricultural water to encourage conservation • Use lined or covered canals that reduce seepage and evaporation. • Use computer monitoring and schedule release of water for maximum efficiency. • Integrate the use of surface water and groundwater to more effectively use the total resource.
Agricultural Use • Irrigate at times when evaporation is minimal, such as at night or in the early morning. • Use improved irrigation systems, such as sprinklers or drip irrigation, that more effectively apply water to crops. • Improve the soil to increase infiltration and minimize runoff. • Encourage the development of crops that require less water or are more salt tolerant.
Domestic Use • Accounts for about 10% of total national water withdrawals • But concentrated in urban areas • May pose major local problems
Domestic Use • Water use can be substantially reduced by: • In semiarid regions, replace lawns with decorative gravels and native plants. • Use more efficient bathroom fixtures. • Turn off water when not absolutely needed. • Flush the toilet only when really necessary. • Fix all leaks quickly.
Domestic Use • Purchase dishwashers and washing machines that minimize water consumption. • Take a long bath rather than a long shower. • Sweep sidewalks and driveways. • Using gray water to water vegetation. • Water lawns and plants at cool times to reduce evaporation.
Domestic Use • Use drip irrigation and place water-holding mulch around garden plants. • Plant drought-resistant vegetation. • Learn how to read the water meter to monitor for unobserved leaks and record your conservation successes. • Use reclaimed water
Industry and Manufacturing Use • Water conservation measures that can be taken by industry: • Using cooling towers that use little or no water • In-plant water treatment and recycling
Perception and Water Use • Perception of water is based partly on its price and availability. • If water is abundant and inexpensive, we don’t think much about it. • If water is scarce or expensive, it is another matter. • E.g. people in Tucson pay about 100% more for water than people in Phoenix. • Tucson residence use less water per person per day
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.