IELTS Writing Task 1 Process Diagram — Band 9 Sample Answer
A process diagram task is unique in Task 1 — it requires passive voice throughout, sequencing language at every stage, and an explanation of what each stage does rather than just its name. This page shows a full band 9 response for an 8-stage water treatment process, with examiner commentary on every criterion.
What does a band 9 IELTS Task 1 process diagram answer look like?
A band 9 process diagram response uses passive voice consistently ('water is pumped', 'chemicals are added'), sequences all stages with linking language ('subsequently', 'following this', 'finally'), explains what happens at each stage rather than just naming it, and opens with an overview that states the number of stages, whether the process is linear or cyclical, and what the final output is. Technical vocabulary from the diagram is used accurately throughout.
Quick Facts
- Task type
- Academic Writing Task 1
- Chart type
- Process diagram (8 stages, linear)
- Word count
- 196 words
- Predicted band
- 9.0
The process stages
Task 1 Question
The diagram below illustrates the process by which rainwater is collected and treated to produce clean drinking water for domestic use.
Collection
Rainwater accumulates in a natural reservoir or purpose-built catchment area
Pumping
Water is pumped from the reservoir to the treatment facility
Screening
Large debris (leaves, sediment) is removed through a mesh screen
Coagulation
Chemicals are added to cause fine particles to clump together (floc)
Sedimentation
The floc settles to the bottom of a settling tank; clarified water rises
Filtration
Water passes through layers of sand and gravel to remove remaining particles
Chlorination
Chlorine is added to kill any remaining bacteria and pathogens
Distribution
Treated water is stored in a clean water reservoir and piped to homes
Band 9 sample answer — 196 words
Band 9 Sample Answer — 196 words
The diagram shows the eight-stage process by which rainwater is collected and purified to produce safe drinking water for households.
Overall, the process is linear and involves two broad phases: an initial collection and removal of physical impurities, followed by chemical treatment to eliminate biological contaminants. The end result is water that is safe for domestic consumption.
In the first stage, rainwater accumulates in a natural reservoir before being pumped to a treatment facility. Here, it passes through a mesh screen where large debris such as leaves and coarse sediment is removed. The water then enters a coagulation chamber, where chemicals are added that cause fine suspended particles to bind together into larger clusters, known as floc.
These clusters subsequently settle to the bottom of a sedimentation tank, allowing the clarified water above to advance to the next stage. The clarified water is then passed through alternating layers of sand and gravel, a filtration process that removes any remaining fine particles. Finally, chlorine is introduced to kill residual bacteria and other pathogens, rendering the water safe for human consumption. The treated water is stored in a clean reservoir before being distributed through pipes to domestic properties.
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Why this answer scores band 9 — examiner breakdown
TA
Task Achievement
- +Overview identifies: 8-stage process, two broad phases (physical removal then chemical treatment), and end result — all without specific stage details
- +All 8 stages described in sequence with correct technical terms: screening, coagulation, floc, sedimentation, chlorination
- +The function of each stage is explained — not just named. 'Chemicals are added that cause fine suspended particles to bind together into larger clusters' explains the coagulation purpose.
C&C
Coherence & Cohesion
- +Logical sequencing: 'In the first stage', 'Here', 'The water then', 'These clusters subsequently', 'then', 'Finally' — clear chronological progression throughout
- +Two-paragraph body structure follows the two-phase overview: physical stages (1–4) → chemical/finishing stages (5–8)
- +Transition between paragraphs: 'These clusters subsequently settle...' picks up directly from the coagulation stage at the end of para 3 — seamless link
LR
Lexical Resource
- +Technical vocabulary used accurately: 'coagulation', 'floc', 'sedimentation', 'chlorination', 'pathogens' — shows field-appropriate lexical range
- +'Fine suspended particles', 'residual bacteria', 'domestic properties' — precise collocations throughout
- +'Rendering the water safe' — participial phrase that avoids a weak 'so the water becomes safe' construction
GRA
Grammatical Range & Accuracy
- +Passive voice used consistently and accurately throughout: 'is pumped', 'is removed', 'are added', 'is introduced' — correct for describing an impersonal technical process
- +Complex sentence: 'chemicals are added that cause fine suspended particles to bind together into larger clusters, known as floc' — relative clause integrated without error
- +Participial phrases: 'allowing the clarified water above to advance', 'rendering the water safe' — advanced structures used accurately
- +Error-free across 196 words
How to structure a band 9 process diagram answer
Introduction
Paraphrase the task. For a process diagram, change 'illustrates' → 'shows', describe what kind of process it is and how many stages.
“'The diagram shows the eight-stage process by which rainwater is collected and purified to produce safe drinking water.'”
Overview — two phases + end result
For a linear process, identify any natural groupings (physical vs chemical, input vs output) and state the final outcome. Number of stages can be in the overview.
“Two broad phases: (1) physical impurity removal, (2) chemical contamination — end result is potable water.”
Body paragraph 1 — first half of the process
Describe stages 1–4 in sequence. Use 'in the first stage', 'here', 'then', 'before' to link stages. Explain what happens at each step.
“Collection → pumped to facility → screening (leaves, sediment) → coagulation (chemicals added, particles clump).”
Body paragraph 2 — second half of the process
Continue from stage 5 to the end. Use 'subsequently', 'then', 'finally' to progress. End with the final outcome.
“Sedimentation → filtration (sand/gravel) → chlorination → clean reservoir → distributed to homes.”
Vocabulary that lifts this answer to band 9
Process diagrams require a specific vocabulary set. These phrases from the sample answer cover the core patterns — learn them as fixed expressions for any process task.
“is pumped to”
Standard passive verb for process diagrams — 'pumped' shows precise technical vocabulary
“fine suspended particles”
Technical collocation for the microscopic debris that coagulation targets — shows precision
“bind together into larger clusters”
Describes the coagulation process with a verb phrase — more precise than 'clump together'
“allowing the clarified water to advance”
Participial phrase of result — explains the consequence of sedimentation elegantly
“rendering the water safe”
'Rendering' (= making) is formal and precise — avoids the weak 'so the water is safe'
“residual bacteria”
'Residual' (= remaining after earlier stages) shows that chlorination is the final purification step
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Frequently Asked Questions
Yes — passive voice is the standard grammatical form for describing industrial or scientific processes in academic English. When there is no specific named agent (nobody in the diagram is doing the pumping — it just happens as part of the process), passive voice is both grammatically correct and natural: 'water is pumped', 'chemicals are added', 'particles are removed'. Using active voice ('workers pump water') when no agent is shown in the diagram is inappropriate.
You should briefly explain what happens at each stage, not just name it. 'Coagulation occurs' scores lower than 'chemicals are added that cause fine particles to bind together into larger clusters'. Explaining the function of each stage demonstrates Task Achievement and Lexical Resource — the two criteria that most often separate band 6 and band 8 process diagram answers.
For a process diagram, the overview typically states: how many stages the process has, whether it is linear or cyclical, and what the starting input and final output are. For example: 'Overall, the process consists of eight sequential stages, beginning with rainwater collection and ending with the distribution of treated drinking water to homes.' Do not include specific stage names in the overview.
Use simple present tense with passive voice: 'water is pumped', 'chemicals are added', 'the water is filtered'. This describes the process as a general, repeatable procedure — which is what a process diagram shows. Do not use past tense (the diagram is not describing a historical event) or future tense.
Use sequencing language throughout: 'In the first stage', 'The water then enters', 'Next', 'Subsequently', 'Following this', 'Finally'. Never use numbers alone ('In step 3') — always combine with a description of what happens. Aim to link each stage to the previous one so the response reads as a continuous description rather than a numbered list.
Sequencing: 'first', 'then', 'subsequently', 'following this', 'finally', 'at this point'. Passive verbs: 'is pumped', 'is filtered', 'is added', 'is removed', 'is transported', 'is converted'. Result language: 'allowing X to', 'resulting in', 'rendering X safe/clean'. Try to use the technical vocabulary specific to the process shown — if the diagram labels a stage 'coagulation', use that term in your answer.
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