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Water Resources

Cycles, treatment, pollution & disease

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The Water Cycle: Stores

Where water lives:

Saltwater stores: Oceans (97% of all water — unusable for drinking)

Freshwater stores: Ice sheets/glaciers, groundwater (aquifers), atmosphere, lakes/rivers

Only ~3% of Earth's water is fresh, and most is frozen. Humans depend on rivers, lakes & groundwater.

The Water Cycle: Transfers

Precipitation: Rain/snow falls from clouds

Interception: Rain trapped by trees/plants

Surface run-off: Water flows downhill (fastest)

Infiltration: Water soaks into soil

Through-flow: Water moves through soil horizontally

Groundwater flow: Water moves through rock layers (slowest)

Evaporation & Transpiration: Water returns to atmosphere

Freshwater Sources

Atmosphere: Rainfall & snow (unreliable, seasonal)

Surface water: Rivers, lakes, reservoirs (visible, easy to access, vulnerable to pollution)

Groundwater: Aquifers & wells (hidden, protected from pollution, but slow to replenish)

Oceans: Desalination plants convert saltwater (expensive, energy-intensive)

Most humans depend on groundwater & surface water.

Water Treatment (4 Stages)

1. Screening: Remove large debris (leaves, twigs, trash)

2. Sedimentation: Let particles settle. Turbidity (cloudiness) reduces.

3. Filtration: Pass through sand/charcoal. Removes smaller particles & chemicals.

4. Chlorination: Add chlorine to kill bacteria. Makes water potable (safe to drink).

Result: Safe, clean drinking water.

Desalination

Two main methods:

Distillation: Boil saltwater, steam rises (pure), condense back to liquid water. Salt left behind.

Reverse Osmosis: Force saltwater through membrane under high pressure. Water passes through, salt blocked.

Benefits: Produces fresh water from unlimited saltwater source

Limitations: Extremely expensive, energy-intensive, leaves toxic brine waste

Used in water-poor regions: Middle East, North Africa, Australia.

Multipurpose Dams: 8 Uses

One dam can provide:

1. Flood control: Store excess water during monsoons
2. Hydro-electric power: Falling water drives turbines
3. Irrigation: Pipe water to farms
4. Water storage: Supply dry seasons

5. Transport: Boats on reservoir
6. Recreation: Boating, fishing tourism
7. Tourism: Famous dam sites
8. Fish farming: Aquaculture in reservoir

Massive economic benefits.

Dam Impacts (Benefits & Limitations)

Benefits: Flood prevention, electricity, water security, jobs, recreation

Limitations: Ecosystem damage, fish migration blocked, methane from decaying biomass, displaces communities, expensive maintenance

Example: Three Gorges Dam (China) — power for 60 million people, but displaced 1.3 million residents.

Water Pollution: Impacts

Sources: Domestic waste, sewage, plastic, industrial discharge, agricultural runoff

Bioaccumulation: Toxic substance builds up in ONE organism over time

Biomagnification: Toxins INCREASE in concentration up the food chain (top predators most affected)

Eutrophication: Excess nutrients → algal bloom → oxygen depletion → dead zone

Mercury, DDT, lead accumulate in fish — dangerous for humans.

Malaria: Mosquitoes & Plasmodium

Disease transmission:

Vector: Female Anopheles mosquito (only females bite)

Pathogen: Plasmodium parasite lives in mosquito & human blood

Cycle: Infected human → mosquito bite → mosquito carries parasite → bites another human → infection spreads

Kills ~627,000 annually. Mostly children in sub-Saharan Africa.

Controlling Malaria

Personal protection:

Mosquito nets (especially at night), insect repellent, vaccination, antimalarial drugs

Vector control:

Drain breeding areas (standing water), spray insecticides, sterilise male mosquitoes, biological control (predatory fish)

Cost-effective nets + education = huge reduction in malaria deaths.

Cholera Control

Cholera = waterborne bacterial disease. Kills through severe diarrhea.

Prevention:

• Handwashing (reduces transmission)
• Adequate sanitation & sewage treatment
• Potable water (boil or chlorinate)
• Vaccination (oral vaccine available)

Clean water + hygiene = cholera disappears.

Endemic in poor regions with no sanitation systems.

Marine Aquaculture

Farming fish, crustaceans, seaweeds in captivity (ocean cages or ponds)

Benefits: Reduces wild fishing pressure, increases food supply, jobs

Risks: Escaped farm fish interbreed with wild, disease outbreaks, pollution from feed waste, nutrient enrichment

Management: Better containment, pollution control, sustainable feed (algae instead of fishmeal)

Oil Pollution

Sources: Oil rigs, tanker spills, pipeline leaks, shipping accidents, tank cleaning

Impacts on wildlife: Coats bird feathers (they drown), chokes fish gills, kills coral, destroys seaweed beds

Prevention (MARPOL): International regulation, double-hulled tankers, risk assessments, maintenance

Response: Booms contain spill, sorbents absorb oil, detergents disperse it, controlled burning

Deepwater Horizon (2010) spilled 4.9 million barrels — ecosystem still recovering.

Plastic Pollution

Conventional plastics: Fossil fuel-based, non-biodegradable (persist 100–1000 years)

Bioplastics: Plant-based, may or may not biodegrade

Microplastics: <5mm fragments from breaking plastic + microbeads in cosmetics

Impacts: Visual pollution, entanglement, mistaken for food, bioaccumulation in marine life

Solutions: Reduce use, ban single-use, recycle, legislation, cleanup initiatives

Summary: Water Management

Sustainable water use:

✓ Protect freshwater sources
✓ Treat water thoroughly before drinking
✓ Control pollution at source
✓ Manage dams responsibly
✓ Control vector diseases (nets, drainage)
✓ Sanitation for cholera prevention
✓ Reduce plastic use
✓ Regulate fishing (aquaculture + wild)

Water scarcity affects 2 billion people.
Protecting water = protecting life.