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Drinking Water Operator Class B Certification Exam Practice Test Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf
- What is the primary purpose of sedimentation in water treatment?
- Remove dissolved solids
- Improve taste and odor
- Remove suspended particles
- Add fluoride
Answer: C
Rationale: Sedimentation allows heavier particles to settle out before
filtration, reducing solids load.
- The most common coagulant used in surface water treatment is: 1 / 4
- Sodium hypochlorite
- Aluminum sulfate (alum)
- Fluorosilicic acid
- Lime
Answer: B
Rationale: Alum is widely used due to effectiveness, availability, and cost
efficiency.
3. Free chlorine residual should ideally be measured after:
- Pre-chlorination
- Flash mixing
- Sedimentation
- Filtration
Answer: D
Rationale: Free chlorine residual is ensured after final treatment steps to
verify disinfection.
- A water tower provides which type of pressure?
- Mechanical
- Pump-created
- Hydrostatic
- Vacuum 2 / 4
Answer: C
Rationale: Elevated storage tanks rely on gravity to create hydrostatic
pressure.
- What is the typical pH range for optimum coagulation with alum?
A. 5.5–7.5
B. 3–4
C. 7.5–9.5
D. 10–12
Answer: A
Rationale: Alum performs best in slightly acidic to neutral pH conditions.
6. The maximum contaminant level (MCL) for nitrate (as N) is:
- 5 mg/L
- 10 mg/L
- 15 mg/L
- 50 mg/L
Answer: B
Rationale: EPA MCL for nitrate is 10 mg/L to prevent methemoglobinemia.
- What is the main purpose of a clearwell? 3 / 4
- Settling
- Provide contact time for disinfection
- Remove iron
- Store sludge
Answer: B
Rationale: Clearwells ensure adequate CT (contact time) for disinfection.
8. The term “headloss” in filtration refers to:
- Water wasted
- Chemical use
- Resistance to flow through a filter
- Loss of pressure from tank elevation
Answer: C
Rationale: Headloss increases as filters accumulate solids.
- Which of the following is a Stage 1 DBP regulated compound?
- Fluoride
- Total trihalomethanes (TTHMs)
- Hardness
- Chloride
Answer: B
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