Water Resources and Pollution Notes

12.1 Water Resources

Section objectives
- Differentiate between common water resources on Earth.
- Water is essential for life; humans cannot survive without it for days.
- Water on Earth can be freshwater or saltwater.
Water in use and its forms
- Water used for drinking and agriculture primarily requires freshwater.
- The Water Cycle
- Earth is nicknamed the 'water planet' due to abundant water in solid, liquid, and gaseous forms.
- Water is a renewable resource, replenished through the water cycle.
- The cycle involves the travel of water molecules between the atmosphere and Earth's surface.
- Oceans play a key role as a large reservoir of water in the cycle.
Global water distribution
- Water covers about $71\%$ of the Earth's surface.
- Approximately $97\%$ of Earth's water is saltwater (oceans and seas).
- About $77\%$ of freshwater is stored in frozen ice caps and glaciers.
- The small portion of freshwater accessible to humans and animals is found in lakes, rivers, and a narrow zone beneath Earth's surface.
Surface water
- Surface water refers to freshwater in rivers, lakes, wetlands, and streams.
- Historically, cities and towns have been built near bodies of water; today, large cities still rely on surface water for livelihoods.
- Uses beyond drinking and irrigation include providing fish, transportation, and hydroelectric power.
River systems
- Rivers form from melting snow on plateaus, hills, plains, and mountains, mixing with streams formed from rainfall.
- A river system is a large network of streams and rivers flowing across a land area.
- Major river systems include the Amazon, Nile, and Mississippi.
Watersheds
- A watershed is a land area drained by a river.
- It can endanger a river if polluted.
- Water input to a watershed varies with melting snow and rainfall.
- Reduced rainfall or melting snow can decrease water reaching a watershed, impacting communities dependent on the river.
Groundwater
- Groundwater is freshwater located beneath Earth's surface in rock formations and sediments.
- It accumulates as water infiltrates the ground during rainfall and eventually reaches a water table.
- In some wet regions, the water table is visible as springs that flow from below the ground.
Aquifers
- An aquifer is an underground formation where groundwater accumulates.
- The upper part is the water table; aquifers consist of gravel, rock, and sand with spaces for water to seep.
- Aquifers can become underground lakes in caves where limestone dissolves.
12.1 Check your understanding
- Question: Nearly what percent of Earth′s water is salt water in oceans and seas?
- Options: $A. 71\%$ $B. 19\%$ $C. 44\%$ $D. 97\%$ $E. 38\%$ $F. 50\%$
- Answer: $D. 97\%$
Porosity and Permeability
- Porosity: the percentage of a rock's total volume that has pores/spaces.
- Rocks with more pores can hold more water; however, water-holding capacity also depends on permeability.
- Permeability: a rock's ability to allow water to flow through it.
- Permeable materials include limestone, sand, gravel, and sandstone.
- Impermeable materials include granite and clay; water cannot flow easily through them.
- Water flows in permeable rocks from pore to pore.
The Recharge Zone
- The recharge zone is where water from the surface percolates down to reach an aquifer.
- It is a sensitive area that should not be polluted, because aquifers would subsequently become polluted.
- Permeability influences how much water percolates into the aquifer.
- Prudent management is required since aquifers can take tens of thousands of years to refill; thus, no buildings should be built on recharge zones.
- Historically, humans have dug wells to reach groundwater.
Wells
- Wells are deep holes drilled below the water table to access groundwater.
- Water is purified as it travels underground.
- Wells may dry up when the water table falls below the well’s level, requiring continual drilling to follow water table changes.

12.2 Water Use and Management

Global context
- Rapid population growth has created a shortage of fresh and clean water.
- The World Health Organization (WHO) estimates that over $1\times 10^9$ people lack access to clean and reliable freshwater.
Global water use by sector
- Water is mainly used for industrial, agricultural, and residential purposes.
- Regional differences exist:
- In Asia, agriculture accounts for $80\%$ of water use, compared with $38\%$ in Europe.
- Europe and North America lead in industrial water use.
- Global shares: industrial use about $19\%$ ; residential use about $8\%$ ; remaining uses include agriculture and other sectors.
Residential and agricultural water use in the U.S.
- A large portion of U.S. freshwater is used for irrigation.
- Residential water use comparison: an average American uses about $300\ \text{L}$ per day; an Indian resident uses about $41\ \text{L}$ per day.
- In the U.S., most residential water is used outdoors (lawn care, watering cars); the rest supports cooking, washing, sanitation, and drinking.
Water treatment
- Water treatment is necessary to make water potable and to remove harmful elements such as arsenic, lead, and mercury.
- Pathogens (bacteria, protozoa, viruses, parasitic worms) are removed during treatment.
Industrial water use
- Water is used in various industries to manufacture goods, generate power, and handle waste disposal.
- Water serves as a major raw material for manufacturing products (e.g., about $1000\ \mathrm{L}$ of water per $1\ \mathrm{kg}$ of aluminum).
- Water is essential for cooling industrial machines.
Agricultural water use
- Agriculture accounts for about $67\%$ of global water use.
- About $80\%$ of agricultural water evaporates before reaching plant roots.
Irrigation
- Irrigation uses water sources other than direct precipitation.
- Early irrigation methods flooded fields from nearby water bodies.
- Modern techniques include water-filled ditches and overhead sprinklers.
- Overhead sprinklers are common in the U.S. but are often uneconomical due to evaporation losses.
Water management projects (historical and modern)
- Romans built canals and aqueducts to move water from mountains to arid areas (Spain and France).
- Modern engineering enables dams and water diversion canals.
- Southwest United States has seen increased settlement due to improved water management.
Water diversion projects
- Diversion projects move water to new areas, expanding supply.
- Example: the Colorado River diverted into canals to supply Arizona, California, and Utah for irrigation and domestic use.
Dams and reservoirs
- A dam is built across a river to control flow and create a reservoir.
- Uses: irrigation, hydroelectric power, drinking water, flood control, recreation.
- About $20\%$ of global electricity comes from hydroelectric power.
- Side effects: potential flooding behind dams, risk of dam failures causing deaths, reduced nutrient flow, and land infertility.
- Approximately $5\times 10^7$ people have been displaced globally due to dam projects.
- Large-scale dam construction is common in China, India, and Brazil.
Water conservation
- Water conservation is the most affordable way to manage resources and ensure access to clean water.
- In agriculture, drip irrigation conserves water by delivering water directly to plant roots through perforated tubing; reduces runoff, seepage, and evaporation.
- Drip irrigation can be enhanced with satellite data to optimize watering times.
Solutions for the future
- Desalination and transportation of freshwater are potential strategies to improve access.
- Desalination converts seawater into freshwater; common in some Middle Eastern countries; often involves heating salty water to evaporate and condense freshwater.
- Desalination is energy-intensive and costly.
- About half of the freshwater in the U.S. is in Alaska.
- Transporting water
- Greek islands use ships to transport freshwater from the mainland in plastic bags.
- In the U.S., there have been discussions about moving water from Alaska to California.
- Towing icebergs as a source of freshwater has been considered but remains unfeasible with current methods.
12.2 Check your understanding
- Question: The amount of water needed to manufacture 1 kg of aluminum is almost $1000\ \mathrm{L}$ .
- Options: A) 50,000 B) 100 C) 5,000 D) 10,000 E) 500 F) 1,000
- Answer: $F\approx 1000\ \mathrm{L}$

12.3 Water Pollution

Section objectives
- Differentiate between point-source pollution and nonpoint-source pollution.
- List the principal water pollutants.
Overview of water pollution
- Caused by physical, chemical, and biological agents that degrade water quality.
- Rapid population growth and industrialization are major causes in developed countries.
- In developing countries, agricultural runoff and sewage disposal are major causes.
- Pollution can originate from point sources or nonpoint sources.
Point-source vs nonpoint-source pollution
- Point-source pollution: pollutant discharged from a single identifiable source (e.g., leaking oil tanker, factory, sewage treatment plant).
- Nonpoint-source pollution: pollutants discharged from various, unidentifiable sources (e.g., runoff from rainfall, land areas river flows through).
- Reducing nonpoint-source pollution requires public awareness of activities causing it (e.g., improper disposal of used motor oil, pesticide spraying).
Principal water pollutants (examples mentioned)
- Wastewater from industries or homes flows to a treatment plant for filtration and treatment.
- Sewage sludge: solid by-product of wastewater treatment; often incinerated or buried in landfills; can be detoxified and used as fertilizer or mixed with clay for building purposes.
- Artificial eutrophication: excessive nutrients in bodies of water due to human activities (e.g., farming, washing). Excessive fertilizer use can cause eutrophication via runoff.
- Eutrophication is a natural process unless caused by human activity; algal blooms symbolize eutrophication and reduce oxygen in water.
- Phosphorus from certain detergents and dishwashing can contribute to eutrophication.
Thermal pollution
- Industries and power plants often discharge warm water after cooling, raising water temperature.
- Higher temperature reduces dissolved oxygen, endangering aquatic life and potentially harming entire ecosystems over time.
Groundwater pollution
- Occurs when pollutants (herbicides, pesticides, fertilizers) percolate through recharge zones into aquifers.
- Leakages from underground storage tanks containing petroleum products or other toxic substances contribute to pollution.
- Unlined landfills, industrial wastewater lagoons, and septic tanks are other pollution sources.
- Groundwater pollution is a challenging environmental problem; remediation via decontamination is slow because water travels through soils and rocks.
Ocean pollution
- Most ocean pollution (about $85\%$ ) originates from inland activities (toxic wastes, medical wastes, oil spills).
- Oceans are also affected by polluted runoff carried by rivers and by ships that dump garbage and wastewater legally in some areas.
- Oil spills: nonpoint sources account for $200{-}300\text{ million gallons}$ annually; tanker accidents account for about $37\text{ million gallons}$ per year; oil spills represent about $5\%$ of ocean pollution.
- Notable incidents: Exxon Valdez (1989) in Prince William Sound, Alaska; a 2001 fuel-oil spill off the Galapagos Islands.
Pollution and ecosystems
- Pollutants can accumulate and lead to biomagnification as they move up the food chain.
- Example: pesticides in plankton are consumed by small fish and then by larger fish, concentrating toxins at higher trophic levels.
Cleaning up and policy responses
- Clean Water Act (1972) aimed to improve water quality in the U.S. following the Cuyahoga River disaster (1969).
- The Act sought to make all surface water suitable for consumption by 1983; progress included improvements in rivers and lakes being suitable for fishing and swimming (around a 30% increase).
- The Cuyahoga River fire of 1969 highlighted the severity of urban water pollution; the text also notes fires on the river in 1952.
- Related legislation:
- Marine Protection, Research, and Sanctuaries Act of 1972 (strengthened ocean pollution controls).
- Oil Pollution Act of 1990 requiring double hulls for all oil tankers using U.S. waters by 2015 to minimize spills.
12.3 Check your understanding
- A factory is a source of point-source pollution.
- Answer: True
Additional notes and connections
- Ethical and practical implications include balancing development with conservation, safeguarding groundwater recharge zones, and addressing the displacement caused by dam projects.
- Real-world relevance includes urban planning near watersheds, irrigation planning, desalination feasibility in arid regions, and policies aimed at reducing nonpoint-source pollution through public awareness and infrastructure.
- Foundational principles related to hydrology (water cycle, watershed concept), geology (porosity, permeability, aquifers), and environmental policy (CWA, OPA) underpin the material.
- Key numerical references used throughout the content include: $71\%$ (Earth's surface covered by water), $97\%$ (saltwater), $77\%$ (freshwater in ice caps/glaciers), $67\%$ (global agricultural water use), $80\%$ (agricultural water evaporates before roots), $20\%$ (hydroelectric share of electricity), $19\%$ (industrial water use), $8\%$ (residential water use), $1000\ \mathrm{L}$ (water required per $1\ \mathrm{kg}$ of aluminum), $2\text{00}$ – $3\text{00}\ \text{million gallons}$ (nonpoint-source oil spills), $37\text{ million gallons}$ (tanker spills), $85\%$ (ocean pollution from inland activities), and $5\%$ (oil spills as a portion of ocean pollution).