Water Treatment Operator Certification
Examination QUESTION AND CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
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1. The primary purpose of coagulation in water treatment is to:
A. Kill pathogens
B. Adjust pH
C. Improve taste
D. Remove suspended particles
Correct Answer: D
Rationale: Coagulation destabilizes fine suspended and colloidal particles
so they can clump together and be removed during sedimentation and
filtration.
2. Which chemical is most commonly used as a coagulant in water treatment
plants?
A. Chlorine
B. Lime
C. Aluminum sulfate (alum)
D. Sodium chloride
Correct Answer: C
Rationale: Alum is widely used because it is effective, economical, and
readily available.
3. The process that follows coagulation is called:
A. Filtration
, B. Flocculation
C. Disinfection
D. Aeration
Correct Answer: B
Rationale: Flocculation gently mixes the water to allow destabilized
particles to form larger flocs.
4. Sedimentation in water treatment primarily relies on:
A. Chemical reactions
B. Gravity
C. Pressure
D. Temperature
Correct Answer: B
Rationale: Sedimentation allows heavier floc particles to settle out of the
water by gravity.
5. Rapid sand filters remove contaminants mainly by:
A. Chemical oxidation
B. Physical straining and adsorption
C. Biological digestion
D. UV radiation
Correct Answer: B
Rationale: Filtration traps particles within the sand media and adsorbs
impurities.
6. Which filter type uses a biological layer to aid in treatment?
A. Rapid sand filter
B. Pressure filter
C. Slow sand filter
D. Multimedia filter
Correct Answer: C
Rationale: Slow sand filters develop a biologically active layer
(schmutzdecke) that enhances pathogen removal.
, 7. Disinfection is primarily intended to:
A. Remove turbidity
B. Reduce hardness
C. Destroy pathogenic organisms
D. Remove iron
Correct Answer: C
Rationale: The main goal of disinfection is to inactivate disease-causing
microorganisms.
8. The most common disinfectant used in water treatment is:
A. Ozone
B. UV light
C. Chloramine
D. Chlorine
Correct Answer: D
Rationale: Chlorine is widely used due to its effectiveness and ability to
maintain a residual.
9. Chlorine residual refers to:
A. Chlorine demand
B. Chlorine remaining after demand is met
C. Total chlorine applied
D. Chlorine lost to evaporation
Correct Answer: B
Rationale: Residual chlorine ensures ongoing disinfection within the
distribution system.
10.The primary purpose of maintaining a chlorine residual is to:
A. Improve taste
B. Prevent corrosion
C. Protect against recontamination
D. Reduce turbidity
Correct Answer: C
Rationale: A residual guards against microbial growth after treatment.
Examination QUESTION AND CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
DOWNLOAD PDF
1. The primary purpose of coagulation in water treatment is to:
A. Kill pathogens
B. Adjust pH
C. Improve taste
D. Remove suspended particles
Correct Answer: D
Rationale: Coagulation destabilizes fine suspended and colloidal particles
so they can clump together and be removed during sedimentation and
filtration.
2. Which chemical is most commonly used as a coagulant in water treatment
plants?
A. Chlorine
B. Lime
C. Aluminum sulfate (alum)
D. Sodium chloride
Correct Answer: C
Rationale: Alum is widely used because it is effective, economical, and
readily available.
3. The process that follows coagulation is called:
A. Filtration
, B. Flocculation
C. Disinfection
D. Aeration
Correct Answer: B
Rationale: Flocculation gently mixes the water to allow destabilized
particles to form larger flocs.
4. Sedimentation in water treatment primarily relies on:
A. Chemical reactions
B. Gravity
C. Pressure
D. Temperature
Correct Answer: B
Rationale: Sedimentation allows heavier floc particles to settle out of the
water by gravity.
5. Rapid sand filters remove contaminants mainly by:
A. Chemical oxidation
B. Physical straining and adsorption
C. Biological digestion
D. UV radiation
Correct Answer: B
Rationale: Filtration traps particles within the sand media and adsorbs
impurities.
6. Which filter type uses a biological layer to aid in treatment?
A. Rapid sand filter
B. Pressure filter
C. Slow sand filter
D. Multimedia filter
Correct Answer: C
Rationale: Slow sand filters develop a biologically active layer
(schmutzdecke) that enhances pathogen removal.
, 7. Disinfection is primarily intended to:
A. Remove turbidity
B. Reduce hardness
C. Destroy pathogenic organisms
D. Remove iron
Correct Answer: C
Rationale: The main goal of disinfection is to inactivate disease-causing
microorganisms.
8. The most common disinfectant used in water treatment is:
A. Ozone
B. UV light
C. Chloramine
D. Chlorine
Correct Answer: D
Rationale: Chlorine is widely used due to its effectiveness and ability to
maintain a residual.
9. Chlorine residual refers to:
A. Chlorine demand
B. Chlorine remaining after demand is met
C. Total chlorine applied
D. Chlorine lost to evaporation
Correct Answer: B
Rationale: Residual chlorine ensures ongoing disinfection within the
distribution system.
10.The primary purpose of maintaining a chlorine residual is to:
A. Improve taste
B. Prevent corrosion
C. Protect against recontamination
D. Reduce turbidity
Correct Answer: C
Rationale: A residual guards against microbial growth after treatment.
