Water Works Operator Class A Licensing
Exam Practice Questions And Correct
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1. What is the primary purpose of coagulation in water treatment?
A. Remove dissolved gases
B. Adjust pH
C. Destabilize suspended particles
D. Remove hardness
Rationale: Coagulation neutralizes particle charges, allowing them to
clump together for removal.
2. Which chemical is most commonly used as a coagulant?
,A. Potassium permanganate
B. Aluminum sulfate (alum)
C. Chlorine dioxide
D. Sodium hydroxide
Rationale: Alum is the most widely used coagulant due to cost-
effectiveness and efficiency.
3. The chlorine demand of water is determined by measuring chlorine
levels after:
A. 5 minutes
B. 10 minutes
C. 15 minutes
D. A standard contact time, typically 30 minutes
Rationale: Demand is found after allowing time for chlorine to react with
impurities.
4. What is the typical pH range for effective chlorination?
A. 2–4
B. 4–5
C. 6.5–7.5
D. 8.5–9.5
Rationale: Chlorine is most effective in slightly acidic to neutral pH ranges.
,5. Excessive headloss in a filter usually indicates:
A. High alkalinity
B. Air binding
C. Filter clogging
D. Too much chlorine
Rationale: Headloss increases as trapped solids restrict flow through the
filter.
6. The purpose of backwashing a filter is to:
A. Remove dissolved minerals
B. Disinfect the filter media
C. Remove accumulated solids from the media
D. Increase turbidity
Rationale: Backwashing loosens and removes solids that have built up in
the media.
7. What does NTU measure?
A. Hardness
B. pH
C. Turbidity
D. Chlorine concentration
, Rationale: NTU (nephelometric turbidity units) measure cloudiness caused
by suspended particles.
8. The most effective disinfectant against Giardia is:
A. Free chlorine
B. Chloramines
C. Ozone
D. Bromine
Rationale: Ozone provides rapid inactivation of protozoan cysts like
Giardia.
9. The maximum contaminant level (MCL) for nitrate (as N) is:
A. 2 mg/L
B. 5 mg/L
C. 10 mg/L
D. 20 mg/L
Rationale: EPA MCL for nitrate is 10 mg/L as nitrogen due to infant
methemoglobinemia risk.
10. The most common cause of pump cavitation is:
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of coagulation in water treatment?
A. Remove dissolved gases
B. Adjust pH
C. Destabilize suspended particles
D. Remove hardness
Rationale: Coagulation neutralizes particle charges, allowing them to
clump together for removal.
2. Which chemical is most commonly used as a coagulant?
,A. Potassium permanganate
B. Aluminum sulfate (alum)
C. Chlorine dioxide
D. Sodium hydroxide
Rationale: Alum is the most widely used coagulant due to cost-
effectiveness and efficiency.
3. The chlorine demand of water is determined by measuring chlorine
levels after:
A. 5 minutes
B. 10 minutes
C. 15 minutes
D. A standard contact time, typically 30 minutes
Rationale: Demand is found after allowing time for chlorine to react with
impurities.
4. What is the typical pH range for effective chlorination?
A. 2–4
B. 4–5
C. 6.5–7.5
D. 8.5–9.5
Rationale: Chlorine is most effective in slightly acidic to neutral pH ranges.
,5. Excessive headloss in a filter usually indicates:
A. High alkalinity
B. Air binding
C. Filter clogging
D. Too much chlorine
Rationale: Headloss increases as trapped solids restrict flow through the
filter.
6. The purpose of backwashing a filter is to:
A. Remove dissolved minerals
B. Disinfect the filter media
C. Remove accumulated solids from the media
D. Increase turbidity
Rationale: Backwashing loosens and removes solids that have built up in
the media.
7. What does NTU measure?
A. Hardness
B. pH
C. Turbidity
D. Chlorine concentration
, Rationale: NTU (nephelometric turbidity units) measure cloudiness caused
by suspended particles.
8. The most effective disinfectant against Giardia is:
A. Free chlorine
B. Chloramines
C. Ozone
D. Bromine
Rationale: Ozone provides rapid inactivation of protozoan cysts like
Giardia.
9. The maximum contaminant level (MCL) for nitrate (as N) is:
A. 2 mg/L
B. 5 mg/L
C. 10 mg/L
D. 20 mg/L
Rationale: EPA MCL for nitrate is 10 mg/L as nitrogen due to infant
methemoglobinemia risk.
10. The most common cause of pump cavitation is:
