Practice Exam Questions And Correct

Water Treatment Operator Class A Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1) The primary purpose of coagulation in water treatment is to:

• Remove dissolved gases
• Destabilize colloidal particles
• Filter out large debris
• Adjust pH

Rationale: Coagulation neutralizes particle charges, allowing them to

clump for removal during flocculation and sedimentation.

2. The most common coagulant used in water treatment is:

• Sodium hypochlorite
• Aluminum sulfate (alum)
• Lime 1 / 3

• Ferric chloride

Rationale: Alum is widely used due to its effectiveness and cost

efficiency.

3. Optimal pH range for alum coagulation is typically:

A) 3–4

B) 5–6

C) 6–7

D) 8–9

Rationale: Alum forms best floc in a slightly acidic to neutral range.

4. A jar test is used to determine:

• Disinfection by-product concentration
• Optimum coagulant dosage
• Filter run time
• Residual turbidity after filtration

Rationale: Jar testing simulates coagulation to find proper dosage

and mixing conditions.

5. Turbidity is most commonly measured in:

• mg/L

B) NTU

C) MPN

• ppm

Rationale: Turbidity is measured in Nephelometric Turbidity Units. 2 / 3

6. The CT concept in disinfection refers to:

• Chlorination technique
• Concentration × Time
• Contamination threshold
• Chemical treatment index

Rationale: CT combines disinfectant concentration and contact time

for pathogen inactivation.

7. The most chlorine-resistant organism from the list is:

• Bacteria
• Viruses
• Giardia
• Cryptosporidium

Rationale: Cryptosporidium oocysts are highly resistant to chlorine.

8. The maximum residual disinfectant level (MRDL) for chlorine is:

• 2.0 mg/L
• 3.0 mg/L
• 4.0 mg/L
• 5.0 mg/L

Rationale: EPA MRDL for chlorine is 4.0 mg/L.

9. Breakpoint chlorination ensures:

• Chloramines remain in water
• Free chlorine residual is available
• DBPs are eliminated
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