Water Treatment Operator Class C
Licensing Exam Practice Test Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A Instant
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1. Which of the following is the primary purpose of coagulation in water
treatment?
A. Remove dissolved gases
B. Remove turbidity and suspended solids
C. Adjust pH
D. Disinfect water
B. Remove turbidity and suspended solids
Rationale: Coagulation destabilizes suspended particles so they can
aggregate into larger particles for removal during sedimentation or
filtration.
2. What is the most common coagulant used in water treatment plants?
A. Sodium hypochlorite
B. Aluminum sulfate (alum)
C. Calcium carbonate
D. Sodium hydroxide
B. Aluminum sulfate (alum)
, Rationale: Alum is widely used due to its effectiveness in forming flocs
that can settle out of water.
3. Which unit process directly follows coagulation in conventional water
treatment?
A. Filtration
B. Sedimentation
C. Chlorination
D. Aeration
B. Sedimentation
Rationale: Sedimentation allows the coagulated flocs to settle out of the
water before filtration.
4. What is the primary purpose of filtration in water treatment?
A. Remove dissolved minerals
B. Remove turbidity and remaining suspended solids
C. Adjust pH
D. Disinfect pathogens
B. Remove turbidity and remaining suspended solids
Rationale: Filtration removes particles too small to settle during
sedimentation, improving water clarity.
5. Which of the following best describes the process of flocculation?
A. Rapid mixing of chemicals
B. Slow gentle mixing to form larger flocs
C. Settling of solids in a tank
D. Passage of water through sand
B. Slow gentle mixing to form larger flocs
Rationale: Flocculation gently agitates water to help small coagulated
particles join together into larger flocs for easier removal.
6. The term "turbidity" in water refers to:
A. Color of water
B. Clarity or cloudiness caused by suspended particles
C. Dissolved oxygen content
, D. pH level
B. Clarity or cloudiness caused by suspended particles
Rationale: Turbidity measures how cloudy water is due to particles; high
turbidity can protect microorganisms from disinfection.
7. What is the typical pH range for effective coagulation using alum?
A. 4.0–5.0
B. 6.0–7.5
C. 8.5–9.5
D. 10.0–11.0
B. 6.0–7.5
Rationale: Alum works best in slightly acidic to neutral water to form
stable flocs.
8. Which process removes iron and manganese from water?
A. Coagulation
B. Oxidation followed by filtration
C. Sedimentation
D. Reverse osmosis
B. Oxidation followed by filtration
Rationale: Oxidizing agents convert dissolved iron and manganese to
insoluble forms, which can then be filtered out.
9. Free chlorine in water treatment refers to:
A. Chlorine combined with ammonia
B. Chlorine available to disinfect
C. Chlorine bound to metals
D. Chlorine after reaction with organic matter
B. Chlorine available to disinfect
Rationale: Free chlorine is uncombined chlorine that can inactivate
pathogens in water.
10.The purpose of adding fluoride to drinking water is to:
A. Disinfect water
B. Improve taste
Licensing Exam Practice Test Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A Instant
Download Pdf
1. Which of the following is the primary purpose of coagulation in water
treatment?
A. Remove dissolved gases
B. Remove turbidity and suspended solids
C. Adjust pH
D. Disinfect water
B. Remove turbidity and suspended solids
Rationale: Coagulation destabilizes suspended particles so they can
aggregate into larger particles for removal during sedimentation or
filtration.
2. What is the most common coagulant used in water treatment plants?
A. Sodium hypochlorite
B. Aluminum sulfate (alum)
C. Calcium carbonate
D. Sodium hydroxide
B. Aluminum sulfate (alum)
, Rationale: Alum is widely used due to its effectiveness in forming flocs
that can settle out of water.
3. Which unit process directly follows coagulation in conventional water
treatment?
A. Filtration
B. Sedimentation
C. Chlorination
D. Aeration
B. Sedimentation
Rationale: Sedimentation allows the coagulated flocs to settle out of the
water before filtration.
4. What is the primary purpose of filtration in water treatment?
A. Remove dissolved minerals
B. Remove turbidity and remaining suspended solids
C. Adjust pH
D. Disinfect pathogens
B. Remove turbidity and remaining suspended solids
Rationale: Filtration removes particles too small to settle during
sedimentation, improving water clarity.
5. Which of the following best describes the process of flocculation?
A. Rapid mixing of chemicals
B. Slow gentle mixing to form larger flocs
C. Settling of solids in a tank
D. Passage of water through sand
B. Slow gentle mixing to form larger flocs
Rationale: Flocculation gently agitates water to help small coagulated
particles join together into larger flocs for easier removal.
6. The term "turbidity" in water refers to:
A. Color of water
B. Clarity or cloudiness caused by suspended particles
C. Dissolved oxygen content
, D. pH level
B. Clarity or cloudiness caused by suspended particles
Rationale: Turbidity measures how cloudy water is due to particles; high
turbidity can protect microorganisms from disinfection.
7. What is the typical pH range for effective coagulation using alum?
A. 4.0–5.0
B. 6.0–7.5
C. 8.5–9.5
D. 10.0–11.0
B. 6.0–7.5
Rationale: Alum works best in slightly acidic to neutral water to form
stable flocs.
8. Which process removes iron and manganese from water?
A. Coagulation
B. Oxidation followed by filtration
C. Sedimentation
D. Reverse osmosis
B. Oxidation followed by filtration
Rationale: Oxidizing agents convert dissolved iron and manganese to
insoluble forms, which can then be filtered out.
9. Free chlorine in water treatment refers to:
A. Chlorine combined with ammonia
B. Chlorine available to disinfect
C. Chlorine bound to metals
D. Chlorine after reaction with organic matter
B. Chlorine available to disinfect
Rationale: Free chlorine is uncombined chlorine that can inactivate
pathogens in water.
10.The purpose of adding fluoride to drinking water is to:
A. Disinfect water
B. Improve taste
