Exam Practice Questions And Correct

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

• What is the primary purpose of coagulation in water treatment?
• Remove dissolved gases
• Adjust pH
• Destabilize suspended particles
• Remove hardness

Rationale: Coagulation neutralizes particle charges, allowing them to

clump together for removal.

• Which chemical is most commonly used as a coagulant? 1 / 4

• Potassium permanganate
• Aluminum sulfate (alum)
• Chlorine dioxide
• Sodium hydroxide

Rationale: Alum is the most widely used coagulant due to cost-

effectiveness and efficiency.

• The chlorine demand of water is determined by measuring chlorine

levels after:

• 5 minutes
• 10 minutes
• 15 minutes
• A standard contact time, typically 30 minutes

Rationale: Demand is found after allowing time for chlorine to react with

impurities.

• 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. 2 / 4

5. Excessive headloss in a filter usually indicates:

• High alkalinity
• Air binding
• Filter clogging
• Too much chlorine

Rationale: Headloss increases as trapped solids restrict flow through the

filter.

6. The purpose of backwashing a filter is to:

• Remove dissolved minerals
• Disinfect the filter media
• Remove accumulated solids from the media
• Increase turbidity

Rationale: Backwashing loosens and removes solids that have built up in

the media.

• What does NTU measure?
• Hardness
• pH
• Turbidity
• Chlorine concentration 3 / 4

Rationale: NTU (nephelometric turbidity units) measure cloudiness caused

by suspended particles.

8. The most effective disinfectant against Giardia is:

• Free chlorine
• Chloramines
• Ozone
• Bromine

Rationale: Ozone provides rapid inactivation of protozoan cysts like

Giardia.

9. The maximum contaminant level (MCL) for nitrate (as N) is:

• 2 mg/L
• 5 mg/L
• 10 mg/L
• 20 mg/L

Rationale: EPA MCL for nitrate is 10 mg/L as nitrogen due to infant

methemoglobinemia risk.

• The most common cause of pump cavitation is:
• / 4