WATER OPERATOR LICENSING EXAMINER EXAM QUESTIONS AND
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2025/2026 Q&A/
INSTANDOWNLOAD PDF
1. What is the primary purpose of coagulation in water treatment?
A. Remove dissolved salts
B. Remove suspended particles
C. Adjust pH
D. Disinfect water
Correct answer: B — Coagulation destabilizes suspended particles, allowing them to clump and
be removed during sedimentation and filtration.
2. Which chemical is most commonly used as a coagulant?
A. Sodium hydroxide
B. Aluminum sulfate (alum)
C. Calcium hypochlorite
D. Sodium carbonate
Correct answer: B — Aluminum sulfate (alum) is the most widely used coagulant to aggregate
fine particles.
3. What is the main purpose of chlorination in water treatment?
A. Remove hardness
B. Remove iron and manganese
C. Disinfect water
D. Reduce turbidity
Correct answer: C — Chlorination kills or inactivates disease-causing microorganisms.
4. The ideal pH for coagulation using alum is approximately:
A. 4.5
B. 5.5–7.5
C. 8.0–9.5
D. 10.0
,Correct answer: B — Alum works best in slightly acidic to neutral conditions for optimum floc
formation.
5. Which type of valve is typically used to control flow in a water main?
A. Gate valve
B. Check valve
C. Globe valve
D. Butterfly valve
Correct answer: C — Globe valves are used for throttling or regulating flow.
6. The chlorine demand of water is defined as:
A. Chlorine remaining after disinfection
B. Chlorine needed to oxidize organic and inorganic materials
C. Chlorine added minus chlorine residual
D. Both B and C
Correct answer: D — Chlorine demand equals the amount used to react with contaminants
before residual chlorine remains.
7. What is the standard unit for measuring turbidity?
A. ppm
B. NTU
C. mg/L
D. μS/cm
Correct answer: B — Turbidity is measured in Nephelometric Turbidity Units (NTU).
8. Which organism is used as an indicator of fecal contamination in water?
A. Giardia
B. E. coli
C. Cryptosporidium
D. Salmonella
Correct answer: B — E. coli is a coliform bacteria indicating fecal pollution.
9. Which of the following is used to soften hard water?
A. Sodium bicarbonate
B. Lime
C. Chlorine
, D. Alum
Correct answer: B — Lime (calcium hydroxide) removes calcium and magnesium hardness
through precipitation.
10. Which law regulates safe drinking water in the United States?
A. Clean Water Act
B. Safe Drinking Water Act
C. Resource Conservation and Recovery Act
D. Clean Air Act
Correct answer: B — The Safe Drinking Water Act (SDWA) sets standards for potable water
quality.
11. Backwashing a filter removes:
A. Dissolved solids
B. Biological growth
C. Trapped particles
D. Minerals
Correct answer: C — Backwashing reverses flow to remove accumulated particles from the filter
media.
12. The minimum chlorine residual in the distribution system should be:
A. 0.1 mg/L
B. 0.2 mg/L
C. 1.0 mg/L
D. 4.0 mg/L
Correct answer: B — 0.2 mg/L ensures continuing disinfection throughout the distribution
system.
13. What is the most common cause of water main breaks?
A. High pH
B. Corrosion
C. Over-chlorination
D. Iron bacteria
Correct answer: B — Corrosion and pressure stress weaken pipes leading to breaks.
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2025/2026 Q&A/
INSTANDOWNLOAD PDF
1. What is the primary purpose of coagulation in water treatment?
A. Remove dissolved salts
B. Remove suspended particles
C. Adjust pH
D. Disinfect water
Correct answer: B — Coagulation destabilizes suspended particles, allowing them to clump and
be removed during sedimentation and filtration.
2. Which chemical is most commonly used as a coagulant?
A. Sodium hydroxide
B. Aluminum sulfate (alum)
C. Calcium hypochlorite
D. Sodium carbonate
Correct answer: B — Aluminum sulfate (alum) is the most widely used coagulant to aggregate
fine particles.
3. What is the main purpose of chlorination in water treatment?
A. Remove hardness
B. Remove iron and manganese
C. Disinfect water
D. Reduce turbidity
Correct answer: C — Chlorination kills or inactivates disease-causing microorganisms.
4. The ideal pH for coagulation using alum is approximately:
A. 4.5
B. 5.5–7.5
C. 8.0–9.5
D. 10.0
,Correct answer: B — Alum works best in slightly acidic to neutral conditions for optimum floc
formation.
5. Which type of valve is typically used to control flow in a water main?
A. Gate valve
B. Check valve
C. Globe valve
D. Butterfly valve
Correct answer: C — Globe valves are used for throttling or regulating flow.
6. The chlorine demand of water is defined as:
A. Chlorine remaining after disinfection
B. Chlorine needed to oxidize organic and inorganic materials
C. Chlorine added minus chlorine residual
D. Both B and C
Correct answer: D — Chlorine demand equals the amount used to react with contaminants
before residual chlorine remains.
7. What is the standard unit for measuring turbidity?
A. ppm
B. NTU
C. mg/L
D. μS/cm
Correct answer: B — Turbidity is measured in Nephelometric Turbidity Units (NTU).
8. Which organism is used as an indicator of fecal contamination in water?
A. Giardia
B. E. coli
C. Cryptosporidium
D. Salmonella
Correct answer: B — E. coli is a coliform bacteria indicating fecal pollution.
9. Which of the following is used to soften hard water?
A. Sodium bicarbonate
B. Lime
C. Chlorine
, D. Alum
Correct answer: B — Lime (calcium hydroxide) removes calcium and magnesium hardness
through precipitation.
10. Which law regulates safe drinking water in the United States?
A. Clean Water Act
B. Safe Drinking Water Act
C. Resource Conservation and Recovery Act
D. Clean Air Act
Correct answer: B — The Safe Drinking Water Act (SDWA) sets standards for potable water
quality.
11. Backwashing a filter removes:
A. Dissolved solids
B. Biological growth
C. Trapped particles
D. Minerals
Correct answer: C — Backwashing reverses flow to remove accumulated particles from the filter
media.
12. The minimum chlorine residual in the distribution system should be:
A. 0.1 mg/L
B. 0.2 mg/L
C. 1.0 mg/L
D. 4.0 mg/L
Correct answer: B — 0.2 mg/L ensures continuing disinfection throughout the distribution
system.
13. What is the most common cause of water main breaks?
A. High pH
B. Corrosion
C. Over-chlorination
D. Iron bacteria
Correct answer: B — Corrosion and pressure stress weaken pipes leading to breaks.
