Chapter 19: Water: A Precious Resource 💧
A Comprehensive Guide for PSTET Paper-2 (Science)
Chapter Overview
| Section | Topic | PSTET Weightage | Page No. |
|:---:|:---|::---:|:---:|
| 19.1 | Availability of Water on Earth | High | 2 |
| 19.2 | Water Cycle | High | 7 |
| 19.3 | Groundwater: Depletion and Recharge (Rainwater Harvesting) | High | 12 |
| 19.4 | Water Management and Conservation | Medium | 18 |
| 19.5 | Water Pollution | High | 23 |
| Practice Zone | MCQs & Pedagogical Questions | - | 30 |
Learning Objectives 🎯
After studying this chapter, you will be able to:
✅ Analyze the distribution of Earth's water and explain why only a tiny fraction is available for human use
✅ Describe the continuous movement of water through the water cycle (hydrological cycle)
✅ Explain the causes of groundwater depletion and evaluate recharge methods like rainwater harvesting
✅ Identify and apply water conservation strategies at individual, community, and policy levels
✅ Classify water pollutants and explain their sources and effects on human health and ecosystems
✅ Apply pedagogical strategies to teach water-related concepts effectively to upper primary students
Pedagogical Link 🔗
For Teachers: This chapter directly aligns with:
Class 7 Science NCERT Chapter 16: "Water: A Precious Resource"
Class 8 Science NCERT Chapter 18: "Pollution of Air and Water"
Teaching Tips:
Begin with a "Water Audit" activity—students track their daily water usage
Use visual models like a 1-liter bottle to demonstrate the tiny fraction of available freshwater
Create a "Mini Water Cycle" in a plastic bag taped to a window
Connect to local issues—discuss water scarcity in your region, recent droughts, or floods
Use case studies of successful rainwater harvesting projects in India
Section 19.1: Availability of Water on Earth 🌍
Introduction
When we look at a map of Earth, we see vast blue oceans covering most of the planet. With about 70% of Earth's surface covered in water, it's easy to assume we have plenty. However, the reality is quite different—only a tiny fraction of this water is available for human use . Understanding this scarcity is the first step toward appreciating water as a precious resource.
19.1.1 The Total Water on Earth
Earth holds approximately 1.386 billion cubic kilometers of water . If all this water were formed into a cube, each side would measure about 1,150 kilometers (715 miles) . This seems like an enormous amount—but the critical question is: how much of this is actually usable?
19.1.2 Distribution of Earth's Water
Table 19.1: Global Water Distribution
Key Takeaways:
Most freshwater is locked in ice sheets and glaciers (Antarctica, Greenland)
The water humans use directly is just 0.014% of all water on Earth
19.1.3 Visualizing Water Availability
The Bucket Analogy:
| Representation | What It Shows |
|---|---|
| 1000 liters (total Earth water) | All water on Earth |
| 25 liters (2.5%) | Total freshwater |
| 17 liters (68% of freshwater) | Frozen in ice caps/glaciers (inaccessible) |
| 7.5 liters (30% of freshwater) | Groundwater (some accessible, some too deep) |
| 0.075 liters (0.3% of freshwater) | Surface water (lakes, rivers) |
| 0.014 liters (14 ml) | Readily accessible for human use! |
This visualization helps students understand why water is truly a precious resource.
19.1.4 The 0.014% Reality
Only about 0.014% of all water on Earth is both fresh and easily accessible in surface and near-surface sources that people can use directly . This tiny fraction—the water in rivers, lakes, and shallow aquifers—must support:
Drinking water for 8 billion people
Agriculture (which accounts for 70% of global freshwater withdrawals)
Industry and manufacturing
Ecosystems and wildlife
19.1.5 Uneven Distribution of Freshwater
Countries with Most Freshwater:
About 60% of the available freshwater is found in just nine countries :
Brazil
Canada
China
Columbia
Democratic Republic of Congo
India
Indonesia
Russia
United States
These nine countries represent about 44% of Earth's landmass and are home to 35% of the global population . Even within these countries, distribution is uneven—creating regional water scarcity.
19.1.6 Water Scarcity Facts
📝 PSTET Note: A recent UN University report describes a shift toward "global water bankruptcy," warning that large parts of the world are now living beyond sustainable water supplies .
19.1.7 Water Stress: Physical vs. Economic
Projection: If water consumption patterns remain consistent, 3.5 billion people could live in water-stressed river basins by 2025 .
19.1.8 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| The 1-Liter Bottle Demo | Fill 1L bottle—remove 30ml for freshwater, then 0.14ml for accessible water | Visual learning |
| World Map Activity | Locate the nine water-rich countries; discuss why distribution matters | Geography connection |
| "My Water Day" Journal | Track personal water use; calculate how many people could be served | Empathy building |
| Local Water Audit | Investigate local water sources, treatment, and challenges | Community connection |
Section 19.2: Water Cycle 🔄
Introduction
Water is constantly moving—through the air, on Earth's surface, and underground. This continuous movement, powered by the Sun's energy, is called the water cycle (or hydrological cycle) . The water we drink today is the same water that existed millions of years ago—it cannot be created or destroyed, only recycled .
19.2.1 What is the Water Cycle?
Definition: The water cycle is a natural process of constantly recycling water through different levels of the ecosystem . Water changes between three states of matter—solid, liquid, and gas—as it moves through the cycle.
Key Principle: The amount of water on Earth remains constant—it simply changes location and form.
19.2.2 The Five Stages of the Water Cycle
Table 19.2: Stages of the Water Cycle
19.2.3 Detailed Explanation of Each Stage
A. Evaporation 💧 → 💨
The Sun's heat provides energy to water molecules
Water at the surface of oceans, lakes, rivers, and even puddles gains enough energy to escape as vapor
Factors affecting evaporation rate: Temperature, humidity, wind speed, surface area
B. Transpiration 🌿 → 💨
Plants absorb water through their roots
Water travels up through the plant and exits through tiny pores (stomata) in leaves
A large oak tree can transpire 40,000 gallons (150,000 liters) of water per year
Together, evaporation and transpiration are sometimes called evapotranspiration
C. Condensation 💨 → 💧
As water vapor rises, it encounters cooler temperatures at higher altitudes
Cooling causes water vapor to change back into tiny liquid droplets
These droplets cluster around dust particles (condensation nuclei)
Clouds are visible masses of these tiny water droplets or ice crystals
D. Precipitation ☁️ → 💧/❄️
When water droplets in clouds grow too heavy to remain suspended, they fall
Forms of precipitation:
Rain (liquid water droplets)
Snow (ice crystals)
Hail (layered ice balls)
Sleet (frozen raindrops)
Precipitation returns water to Earth's surface
E. Collection and Runoff 🌊
Precipitation that reaches land takes several paths:
| Path | Description | Percentage |
|---|---|---|
| Runoff | Water flows over land into streams, rivers, lakes, oceans | Varies |
| Infiltration | Water soaks into ground, becoming soil moisture or groundwater | Varies |
| Evaporation | Some water evaporates immediately from surfaces | Varies |
19.2.4 How Long Water Stays in Different Reservoirs
The residence time of water varies greatly depending on where it is :
| Location | Average Residence Time |
|---|---|
| Atmosphere | Less than 1 week |
| Rivers | 2 weeks |
| Lakes | 2 weeks to 100 years |
| Oceans | 3,200 years |
| Glaciers/Ice caps | 20-100 years (mountain glaciers) to 400,000 years (Antarctica) |
| Groundwater (shallow) | 100-200 years |
| Groundwater (deep) | 10,000+ years |
📝 PSTET Note: In a 100-year period, a water molecule spends 98 years in the ocean, 20 months as ice, about 2 weeks in lakes and rivers, and less than a week in the atmosphere .
19.2.5 The Water Cycle and Climate
The water cycle is driven by solar energy and gravity. It plays a crucial role in:
Climate regulation (water absorbs and releases heat)
Weather patterns (cloud formation, precipitation)
Distribution of fresh water around the planet
19.2.6 Classroom Activity: Make a Mini Water Cycle
| Step | Procedure |
|---|---|
| 1 | Take a clear ziplock plastic bag |
| 2 | Add a small amount of water (enough to cover bottom) |
| 3 | Add a few drops of blue food coloring (optional) |
| 4 | Seal the bag tightly |
| 5 | Tape the bag to a sunny window |
| Observation | Water evaporates, condenses on bag, and "rains" back down |
19.2.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Water Cycle Diagram | Students draw and label the water cycle | Visual learning |
| Role Play | Students act as water molecules moving through stages | Kinesthetic learning |
| Mini Water Cycle | Bag activity as described above | Hands-on learning |
| Local Connection | Trace where your local water comes from and where it goes | Real-world application |
Section 19.3: Groundwater: Depletion and Recharge (Rainwater Harvesting) 🌊
Introduction
Beneath our feet lies one of Earth's most important freshwater sources—groundwater. Stored in underground layers called aquifers, groundwater supplies drinking water to billions and irrigation water for much of the world's food. But this hidden resource is being depleted at alarming rates .
19.3.1 What is Groundwater?
Definition: Groundwater is water that exists beneath Earth's surface in pores between soil particles and in cracks in bedrock. It accumulates in geological formations called aquifers.
Key Facts:
Groundwater occurs almost everywhere beneath the land surface
It provides drinking water for nearly 50% of the global population
In the U.S., 70% of fresh groundwater withdrawals are for irrigation
19.3.2 Groundwater Depletion: Causes
Groundwater depletion occurs when water is pumped from aquifers faster than natural recharge can replace it .
Table 19.3: Major Causes of Groundwater Depletion
19.3.3 Consequences of Groundwater Depletion
📝 PSTET Note: Groundwater depletion is a classic example of the "tragedy of the commons" —individual users acting in their own interest deplete a shared resource.
19.3.4 Groundwater Recharge
Definition: Groundwater recharge is the process by which water moves downward from surface water to groundwater .
A. Natural Recharge
| Source | Process |
|---|---|
| Rainwater infiltration | Rain soaks into soil and percolates down to water table |
| Snowmelt | Melting snow infiltrates into ground |
| Lakes and rivers | Water seeps from surface water bodies into aquifers |
B. Managed/Artificial Recharge
Definition: Artificial recharge (also called managed aquifer recharge) is the practice of intentionally adding water to an aquifer to augment groundwater availability .
| Method | Description |
|---|---|
| Rainwater Harvesting | Collecting and storing rainwater for later use or direct recharge |
| Check Dams | Small dams built across streams to slow water flow and enhance infiltration |
| Percolation Tanks | Excavated ponds that collect water and allow it to seep into ground |
| Recharge Wells | Wells specifically designed to inject water into aquifers |
| Flood Spreading | Diverting flood water onto land to increase infiltration |
19.3.5 Rainwater Harvesting: A Detailed Look
Rainwater harvesting has been practiced since the dawn of some of the oldest civilizations . It is a supply-side intervention to augment groundwater availability and reliability of water supply .
A. Objectives of Rainwater Harvesting
B. Methods of Rainwater Harvesting
Rooftop Rainwater Harvesting (Urban):
| Component | Function |
|---|---|
| Catchment (roof) | Area where rain falls |
| Gutters and downpipes | Channel water from roof |
| First flush device | Diverts initial dirty water |
| Filter | Removes debris and contaminants |
| Storage tank OR | Stores water for direct use |
| Recharge pit/well | Directs water into ground |
Rural/Community Methods:
| Method | Description |
|---|---|
| Check Dams | Small barriers across streams slow water, allowing infiltration |
| Percolation Ponds | Excavated areas that collect runoff and let it seep |
| Contour Bunding | Earth embankments along contours trap water, increase infiltration |
| Recharge Shafts | Boreholes filled with permeable material to direct water to aquifers |
19.3.6 Rainwater Harvesting in India: Success Stories
India has a long tradition of rainwater harvesting. Ancient civilizations like the Indus Valley had sophisticated water management systems .
| Traditional Method | Region | How It Works |
|---|---|---|
| Johads | Rajasthan | Earthen check dams that capture monsoon rain |
| Kunds | Rajasthan | Covered tanks that collect rainwater for drinking |
| Stepwells (Baoris) | Gujarat, Rajasthan | Wells with steps for access; collect rainwater and groundwater |
| Eris (Tanks) | Tamil Nadu | Ancient tank systems for irrigation and recharge |
| Ahar-Pyne | Bihar | Floodwater harvesting system |
Modern Example: In Gujarat, the construction of thousands of check dams under the "Sardar Patel Participatory Water Conservation Scheme" has significantly increased groundwater levels in several districts.
19.3.7 Challenges and Considerations
| Challenge | Consideration |
|---|---|
| Cost | Initial investment required for structures |
| Maintenance | Harvesting systems require regular cleaning |
| Water Quality | First flush must be diverted; filters needed |
| Space | Urban areas may lack space for storage/recharge |
| Geology | Not all areas are suitable for recharge (e.g., clay soils) |
📝 PSTET Note: While rainwater harvesting is valuable, it should not be seen as a substitute for sustainable water use—it is part of an integrated approach .
19.3.8 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Simple Recharge Model | Use jar with sand/gravel, pour water, observe infiltration | Hands-on learning |
| Rooftop Harvesting Calculation | Calculate potential harvest from school roof (Area × rainfall × coefficient) | Math integration |
| Traditional Methods Research | Students research local traditional water harvesting methods | Cultural connection |
| School Rainwater Harvesting | If available, show students how it works | Real-world learning |
Section 19.4: Water Management and Conservation 🚰
Introduction
With water scarcity affecting billions of people, managing this precious resource wisely is essential. Water conservation is not just about using less—it's about using water more efficiently, reducing waste, and protecting water quality for future generations .
19.4.1 Direct vs. Indirect Water Use
Understanding how we use water helps identify conservation opportunities .
| Type | Definition | Examples |
|---|---|---|
| Direct Water Use | Water used directly from the tap | Drinking, bathing, cooking, cleaning |
| Indirect Water Use (Virtual Water) | Water used to produce goods we consume | Food production, manufacturing, electricity generation |
1 pound of beef = 1,799 gallons of water
1 pound of chocolate = 3,170 gallons
1 slice of bread = 11 gallons
1 apple = 18 gallons
1 gallon of wine = 1,008 gallons
1 gallon of corn ethanol = 170 gallons (vs. 5 gallons for gasoline)
19.4.2 Water Conservation Strategies
A. Individual/Household Level
Table 19.4: Household Water Conservation Tips
| Area | Strategy | Potential Savings |
|---|---|---|
| Bathroom | Shorten showers (5 minutes instead of 10) | 25 gallons saved per shower |
| Turn off tap while brushing teeth | 3-5 gallons per minute | |
| Install low-flow showerheads and toilets | Up to 40% reduction | |
| Fix leaky faucets promptly | 170+ gallons/day per drip! | |
| Kitchen | Run dishwasher only when full | 4-10 gallons per load |
| Keep drinking water in refrigerator instead of running tap | Saves running water | |
| Thaw food in refrigerator, not under running water | Saves water, safer food | |
| Laundry | Wash full loads only | 41 gallons per load |
| Use cold water when possible | Saves water and energy | |
| Yard/Garden | Water early morning or late evening | Reduces evaporation loss |
| Use native/drought-tolerant plants (xeriscaping) | Significant reduction | |
| Mulch garden beds | Retains soil moisture | |
| Collect rainwater for plants | Free water! |
B. Agricultural Level
Agriculture accounts for 70% of global freshwater withdrawals . Conservation here has enormous impact.
C. Industrial and Municipal Level
19.4.3 Leaks: The Hidden Waste
19.4.4 Virtual Water and Food Choices
Making informed choices about what we eat can significantly reduce our water footprint .
| Food Choice | Water Footprint |
|---|---|
| Beef | 1,799 gallons/pound |
| Chicken | 518 gallons/pound |
| Vegetables | 39 gallons/pound (average) |
| Grains | 200-300 gallons/pound |
📝 PSTET Note: "Our paper shows that each of us can play a role in protecting our limited water resources for agriculture, by supporting precision farming, choosing crops that suit our local climate, cutting down on food waste and even being more mindful about what we eat" .
19.4.5 Policy and Governance
📝 PSTET Note: 263 rivers either cross or demarcate international political boundaries —requiring cooperation.
19.4.6 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Water Audit Project | Students track family water use for one week | Real-world math |
| Virtual Water Calculator | Calculate water footprint of a meal | Eye-opening activity |
| Leak Detection | Check school for leaks; calculate waste | Hands-on investigation |
| Conservation Poster Campaign | Create awareness posters for school | Creative learning |
Section 19.5: Water Pollution ☣️
Introduction
Water pollution—the contamination of water bodies by harmful substances—is one of the most serious environmental challenges of our time. It threatens human health, destroys ecosystems, and reduces the availability of safe water .
19.5.1 What is Water Pollution?
Definition: Water pollution is the contamination of water bodies (lakes, rivers, oceans, aquifers) by substances that degrade water quality and make it harmful for human use and ecosystem health.
19.5.2 Classification of Water Pollutants
Water pollutants can be classified in several ways :
Table 19.5: Major Categories of Water Pollutants
19.5.3 Major Sources of Water Pollution
A. Point Sources
Definition: Pollutants discharged from a single, identifiable source.
| Source | Examples |
|---|---|
| Industrial facilities | Factories discharging wastewater |
| Sewage treatment plants | Treated (or untreated) effluent |
| Oil spills | Tankers, pipelines |
| Mining operations | Acid mine drainage |
B. Non-Point Sources
Definition: Pollution that comes from many diffuse sources—harder to identify and control.
| Source | Description |
|---|---|
| Agricultural runoff | Fertilizers, pesticides, animal waste washed into water bodies |
| Urban runoff | Oil, chemicals, litter washed from streets during rain |
| Atmospheric deposition | Pollutants from air settle into water |
| Septic systems | Failing systems leak nutrients and pathogens |
19.5.4 Effects of Water Pollution
A. Human Health Effects
Long-term exposure to water pollutants presents significant health risks .
📝 PSTET Note: There is a significant association between water pollutant exposure and disorders in both aquatic life and human health .
B. Environmental Effects
19.5.5 Major Water Pollution Issues in India
| Issue | Description |
|---|---|
| River Pollution | Many rivers (especially Ganga, Yamuna) heavily polluted with sewage, industrial waste |
| Groundwater Contamination | Arsenic in West Bengal, Bihar, UP; Fluoride in Rajasthan, Gujarat, Andhra Pradesh; Nitrate in agricultural areas |
| Coastal Pollution | Industrial and urban discharge affects marine ecosystems |
| Lake Eutrophication | Many urban lakes choked with algal blooms |
19.5.6 Solutions and Remediation Technologies
A. Pollution Prevention
| Approach | Examples |
|---|---|
| Wastewater Treatment | Sewage treatment plants; industrial effluent treatment |
| Cleaner Production | Industries reducing waste at source |
| Agricultural Best Practices | Precision fertilizer application; buffer zones near water |
| Plastic Waste Management | Reduce, reuse, recycle; ban microbeads |
B. Remediation Technologies
📝 PSTET Note: Developing cost-effective and advanced conservation technologies is essential for the availability of safe water .
19.5.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Local Water Testing | Test local water sources (if safely possible) for pH, turbidity | Scientific investigation |
| Pollution Source Mapping | Map potential pollution sources in community | Real-world connection |
| Wastewater Treatment Model | Build simple filter using sand, gravel, charcoal | Hands-on learning |
| Case Study Analysis | Study a polluted river (Ganga, Yamuna) and cleanup efforts | Critical thinking |
Chapter Summary: Key Points for Revision 📝
Quick Revision Table
Practice Zone: PSTET-Style Questions 🎯
Content-Based MCQs
Q1. Approximately what percentage of Earth's water is freshwater?
a) 97%
b) 50%
c) 2.5%
d) 10%
Q2. Which stage of the water cycle involves water changing from liquid to gas?
a) Condensation
b) Precipitation
c) Evaporation
d) Collection
Q3. Groundwater depletion is primarily caused by:
a) Too much rainfall
b) Over-extraction exceeding natural recharge
c) Increased cloud cover
d) More trees planting
Q4. Rainwater harvesting helps by:
a) Increasing pollution
b) Augmenting groundwater storage
c) Reducing rainfall
d) Increasing evaporation
Q5. Which sector accounts for the largest share of global freshwater withdrawals?
a) Domestic use
b) Industry
c) Agriculture (70%)
d) Navigation
Q6. The water required to produce goods we consume is called:
a) Direct water
b) Virtual water
c) Grey water
d) Blue water
Q7. Which of the following is a health effect of heavy metal pollution in water?
a) Improved digestion
b) Neurological disorders
c) Stronger bones
d) Better eyesight
Q8. Eutrophication is caused by excess _______ in water bodies.
a) Oxygen
b) Nutrients (nitrogen, phosphorus)
c) Carbon dioxide
d) Salt
Q9. The traditional rainwater harvesting structures of Rajasthan are called:
a) Johads
b) Stepwells
c) Eris
d) Ahar-pyne
Q10. How many people lacked safely managed drinking water as of 2024?
a) 500 million
b) 1 billion
c) 2.1 billion
d) 5 billion
Pedagogical MCQs
Q11. A teacher wants to demonstrate the tiny fraction of accessible freshwater. The best activity is:
a) Show a pie chart
b) Use a 1-liter bottle to represent all water, then show 0.014% (a drop) as accessible
c) Lecture about percentages
d) Show a video
Q12. To teach the water cycle effectively, the most engaging approach is:
a) Draw diagram on board
b) Have students create a mini water cycle in a ziplock bag
c) Give definitions to memorize
d) Show pictures only
Q13. A student asks, "Why should we save water if 70% of Earth is covered with water?" The best explanation is:
a) "Most water is salty or frozen—only a tiny fraction is usable"
b) "Just because"
c) "Water is expensive"
d) Ignore the question
Q14. While teaching rainwater harvesting, the best real-world connection is:
a) Show diagrams only
b) If available, take students to see a rainwater harvesting system at school or nearby
c) Read from textbook
d) Show a video of rain
Q15. The most effective way to teach about virtual water is:
a) Give definitions
b) Have students calculate the water footprint of their breakfast
c) Show a chart
d) Lecture about it
Answer Key with Explanations
Pedagogical Reflection for Teachers 🤔
Think-Pair-Share Activity:
Think: How would you explain to students that the water they drink today could have been part of a dinosaur's bath millions of years ago?
Pair: Discuss with a colleague how you would design a "Water Conservation Week" for your school with activities for different grade levels.
Share: Design a 15-minute activity to demonstrate groundwater depletion and recharge using simple materials (sponge, water, tray).
NCERT Textbook Linkages 📚
| Class | Chapter | Topic |
|---|---|---|
| Class 7 | Chapter 16 | Water: A Precious Resource |
| Class 8 | Chapter 18 | Pollution of Air and Water |
| Class 9 | Chapter 14 | Natural Resources |
Chapter End Notes
Key Terminology Glossary
Quick Tips for PSTET Aspirants ⚡
✅ Memorize with Mnemonics:
Water Distribution: "Salt Frozen Ground Surface" = Salt water (97%), Frozen (2%), Groundwater (0.75%), Surface (0.014% usable!)
Water Cycle Stages: "Every Tiny Cloud Produces Rain" = Evaporation, Transpiration, Condensation, Precipitation, Runoff
Groundwater Depletion Causes: "Agriculture, Population, Urbanization, Industry, Climate" = A P U I C
Pollutant Categories: "Pathogens, Organic, Heavy metals, Nutrients, Sediments, Pharmaceuticals, Plastics, Radioactive, Thermal" = P O H N S P P R T
✅ Common Exam Traps:
Water cycle does NOT create new water—it recycles existing water
Groundwater depletion is NOT caused by less rainfall alone—over-pumping is main cause
Rainwater harvesting does NOT solve all water problems—it's part of integrated approach
Virtual water is often larger than direct water use—food choices matter!
Eutrophication is caused by NUTRIENTS (N, P), not just any pollution
✅ Important Facts:
1 in 6 gallons lost to leaks before reaching customers in US
~4 billion people experience water scarcity at least one month/year
Answers to "Check Your Understanding"
[To be filled by student]
📝 Note for Self-Study: After completing this chapter, ensure you can:
Explain the distribution of Earth's water with percentages
Draw and label the water cycle with all five stages
List 3 causes and 3 consequences of groundwater depletion
Explain how rainwater harvesting works and give 2 examples
List 5 household water conservation tips
Define virtual water and give 3 examples of water footprints
Classify water pollutants into 5 categories with examples
Describe 3 health effects of water pollution
Explain eutrophication and its causes
