water and waste
4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.
Lesson Overview
Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA
Learning Objectives
- Explain the key ideas of water and waste
- Apply water and waste to exam-style questions
- Develop independent study skills
- Build cross-topic connections
Prerequisites
- Read the revision notes for water and waste first (GCSE Revise summary)
- Key vocab to pre-teach: Potable water, Desalination, Waste water
- Basic skills: reading the summary notes and answering the practice questions there
Materials & Equipment
- Exercise book, coloured pens
- Scientific calculator
- Ruler
- Printed revision notes (link below)
- Internet for videos (see Resources)
Lesson 1: Introduction: water and waste
Duration: 50 minutes
Starter Activity (5 minutes)
Quick Recall
Write down everything you already know about water and waste. Then check against the key terms: Potable water, Desalination, Waste water. Use a mini-whiteboard or paper.
Main Content (35 minutes)
Parent/Teacher Guide:
Before lesson: Read the script below. Pre-teach key vocab: Potable water, Desalination, Waste water.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Before lesson: Read the script below. Pre-teach key vocab: Potable water, Desalination, Waste water.
If stuck: Re-read the revision notes (link above), then break the content into smaller steps.
Extension: See the Stretch & Challenge ideas in Lesson 4.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: water and waste. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Chemistry because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
Mins 0-5 - Hook: "Today: water and waste. By the end you will be able to answer exam questions on it unaided. It connects to the rest of Chemistry because the ideas here recur across the spec."
Mins 5-20 - Direct Instruction: Work through the core ideas below one at a time; after each, ask your student to explain it back in their own words.
Mins 20-30 - Guided Practice: Model the worked example together, then let your student attempt the first practice question with guidance.
Mins 30-35 - Independent Practice: 2-3 practice questions from Lesson 3 below, with immediate feedback.
First Look
Start with the revision notes summary, then attempt: Explain the difference between potable water and pure water.
Plenary (5 minutes)
Check Out
Your student states one thing they learned and one question they still have about water and waste.
Lesson 2: Core Concepts: water and waste
Duration: 50 minutes
Starter Activity (5 minutes)
Review Previous Lesson
Quick recap: write 3 key points from Lesson 1 on water and waste. Check them against the notes below.
Main Content (35 minutes)
Potable water: is water that is safe to drink . It is NOT the same as pure water — potable water contains dissolved substances . It must have low enough levels of dissolved salts and microbes to be safe for human consumption.
In the UK, fresh water from lakes, rivers and underground aquifers is treated to make it potable. The process involves: filtration , sedimentation , and chlorination .
Desalination: removes salt from sea water to produce potable water. Methods include reverse osmosis and distillation . Both are expensive because they require a lot of energy. Desalination is used in dry countries where fresh water is scarce.
Waste water: (sewage) must be treated before being released into the environment. Treatment involves: screening , sedimentation , biological (aerobic) treatment , and anaerobic digestion .
NPK fertilisers: provide plants with the essential elements nitrogen (N) , phosphorus (P) and potassium (K) . They increase crop yields but can cause eutrophication if they enter waterways.
Eutrophication sequence: Fertilisers run off into rivers and lakes. Excess nutrients cause rapid growth of algae (algal bloom) on the water surface. Algae block sunlight, so plants below the surface die. When the algae die, bacteria decompose them using aerobic respiration. Bacteria use up dissolved oxygen in the water. Fish and other aquatic organisms die due to lack of oxygen.
| Term | Meaning | Example |
|---|---|---|
| Pure water | Contains only H₂O molecules (no dissolved substances); boils at exactly 100°C | |
| Potable water | Safe to drink; contains some dissolved substances but at safe levels; no harmful microbes | |
| Distilled water | Pure water produced by distillation — no dissolved substances at all | |
| Distillation | Boil sea water, condense the pure water vapour | Produces very pure water |
| Reverse osmosis | Sea water forced through a semi-permeable membrane under high pressure; salt left behind | Does not require heating |
Practice (10 minutes)
Q: Explain the difference between potable water and pure water.
Answer: Potable water is safe to drink but is not pure — it contains dissolved substances at safe levels and no harmful microbes. Pure water contains only H₂O molecules with no dissolved substances; it boils at exactly 100°C.
Plenary (5 minutes)
Explain Back
Your student teaches the key points back to you without looking. Fill any gaps immediately.
Lesson 3: Application: water and waste
Duration: 50 minutes
Starter Activity (5 minutes)
Quick Recall
Recall the key terms: Potable water, Desalination, Waste water. Define each in one sentence.
Main Content (35 minutes)
Parent/Teacher Guide: Let your student attempt each question alone first, then compare with the model answer. Award method marks for correct working even if the final answer is wrong.
Q1: Explain the difference between potable water and pure water.
Answer: Potable water is safe to drink but is not pure — it contains dissolved substances at safe levels and no harmful microbes. Pure water contains only H₂O molecules with no dissolved substances; it boils at exactly 100°C.
Q2: Describe the three stages of water treatment used to produce potable water from fresh water sources.
Answer: (1) Filtration — water passes through sand/gravel filters to remove solid particles. (2) Sedimentation — aluminium sulfate is added so fine particles clump and settle out. (3) Chlorination — chlorine is added to kill microbes, making the water safe to drink.
Q3: Higher Compare distillation and reverse osmosis as methods of desalination. Explain why desalination is more expensive than treating fresh water.
Answer: Distillation involves boiling sea water and condensing the vapour; reverse osmosis forces water through a semi-permeable membrane at high pressure, leaving salt behind. Both are expensive because they require large amounts of energy — distillation needs heat, reverse osmosis needs high pressure. Treating fresh water is cheaper because filtration, sedimentation and chlorination use much less energy.
Q4: Describe the stages of waste water treatment. How can energy be produced during the process?
Answer: (1) Screening removes large solids. (2) Sedimentation separates sludge from effluent. (3) Aerobic bacteria digest organic matter in the effluent. (4) Anaerobic bacteria digest the sludge, producing methane gas . The methane can be burned to generate electricity or heat.
Q5: Explain how the use of fertilisers can lead to eutrophication and the death of fish in a lake.
Answer: Fertilisers run off farmland into lakes. The excess nutrients cause rapid growth of algae (algal bloom). The algae block sunlight so underwater plants die. When the algae die, bacteria decompose them , using aerobic respiration which consumes dissolved oxygen . The oxygen levels fall so low that fish die .
Plenary (5 minutes)
Error Review
Review any questions answered incorrectly. Identify whether the error was knowledge, method, or reading the question.
Lesson 4: Exam Practice: water and waste
Duration: 50 minutes
Starter Activity (5 minutes)
Command Words
Review what these command words require: state (one point), describe (say what happens), explain (say why), compare (both sides), evaluate (judgement).
Main Content (35 minutes)
Extended Answer
Extended question: Extended Answer 6 marks: Describe how fresh water is treated to make it potable in the UK. Explain why treating sea water to make it potable is more expensive, and describe one method of desalination. <div class="
In the UK, fresh water from rivers, lakes and aquifers is treated in three stages. First, filtration removes solid particles — the water is passed through beds of sand and gravel. Second, sedimentation involves adding aluminium sulfate to make fine particles clump together (flocculation) and settle to the bottom as sediment. Third, chlorination involves adding chlorine to kill harmful microbes (bacteria), making the water safe to drink. Treating sea water (desalination) is more expensive because both methods require large amounts of energy. In distillation, the sea water must be heated to boiling, which requires significant fuel. In reverse osmosis, very high pressure is needed to force water through a semi-permeable membrane, leaving the salt behind. This pressure is generated by pumps that consume large amounts of electricity. Fresh water treatment is cheaper because filtration, sedimentation and chlorination all use relatively little energy compared to boiling water or generating high pressure. Mark scheme: 1 mark for filtration (removes solids); 1 mark for sedimentation (aluminium sulfate, particles clump); 1 mark for chlorination (kills microbes); 1 mark for explaining why des
Exam Tips: Don't confuse potable water with pure water — potable water is safe to drink but NOT pure | For water treatment, learn the three stages in order: filtration → sedimentation → chlorination | For eutrophication, use the full sequence — don't skip steps, examiners look for the complete chain | Desalination is expensive because of ENERGY requirements — always mention this | Waste water treatment produces METHANE from anaerobic digestion — this can be used as fuel
Common Errors: Watch Out! 1. Wrong: Potable water is pure water Correct: Potable water is SAFE to drink but is NOT pure — it contains dissolved substances at safe levels. Pure water has NOTHING dissolved in it 2. Wrong: Chlorination kills all substances in water Correct: Chlorination only kills MICROBES (bacteria) — it does NOT remove dissolved substances or solid particles. Filtration and sedimentation are needed for those 3. Wrong: In eutrophication, fertilisers directly kill fish Correct: Fertilisers cause algal blooms → algae die → bacteria decompose them → bacteria use up oxygen → fish die from LACK OF OXYGEN. The fertilisers do not directly kill the fish 4. Wrong: Distillation and evaporation are the
AO3 - Reasoning & Interpretation: Distillation plant: costs £500 million to build, uses 15 kWh of energy per m³ of water, produces 10,000 m³/day | Reverse osmosis plant: costs £300 million to build, uses 4 kWh of energy per m³ of water, produces 10,000 m³/day
Stretch & Challenge (Grade 8-9):
- Synoptic links: explain how water and waste connects to another Chemistry topic you have studied
- Real-world: research one real-world use or example of water and waste
- Critical: "What are the limitations of the models used in water and waste?"
Plenary (5 minutes)
Assessment Criteria
- Got it: Confident explanation + correct worked examples
- Getting there: Main points OK, needs support with detail
- Not yet: Confused on key concepts - re-run Lesson 2
Homework & Consolidation
- Consolidation: Re-answer any Lesson 3 practice questions answered incorrectly (20 mins)
- Retrieval: Write flashcards for the key terms: Potable water, Desalination, Waste water (10 mins)
- Exam practice: One past-paper question on water and waste from the board websites (15 mins)
- Extension: Explain water and waste to someone else in your own words (10 mins)