Licensing Exam Practice Questions And

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

1. The primary purpose of coagulation in water treatment is:

• Remove dissolved minerals
• Destabilize colloidal particles
• Add disinfectant
• Adjust pH

Rationale: Coagulation neutralizes particle charges so they can

clump together.

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

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

• Potassium permanganate

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

3. Turbidity is typically measured in:

• mg/L

B. NTU

• ppm
• % by volume

Rationale: Nephelometric Turbidity Units measure how particles

scatter light.

4. The minimum chlorine contact time required depends mainly on:

• Hardness
• Conductivity
• Temperature and pH
• Alkalinity

Rationale: Disinfection efficiency changes with pH and water

temperature.

5. A chlorine residual means:

• Too much chlorine was added
• Chlorine has evaporated
• Some disinfecting power remains in the distribution system
• Chlorine is depleted

Rationale: Residual ensures continued protection against pathogens. 2 / 3

6. The most effective chlorine form at low pH is:

• Chloride ion
• Hypochlorous acid (HOCl)
• Hypochlorite ion
• Chloramine

Rationale: HOCl is a stronger and faster disinfectant.

• What unit is used to measure water hardness?

A. NTU

• mg/L as CaCO₃
• mL/min
• ft/sec

Rationale: Hardness is expressed as calcium carbonate equivalent.

8. Lime softening primarily removes:

• Microbes
• Silica
• Calcium and magnesium
• Iron

Rationale: Lime raises pH causing calcium and magnesium to

precipitate.

9. A grab sample is:

• Collected every hour
• A single sample taken at one point in time
• A monthly composite
• / 3