Licensing Exam Practice Questions And

Public Water System 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?

a) Remove dissolved gases

b) Remove suspended solids

c) Disinfect water

d) Adjust pH

Answer: b) Remove suspended solids

Rationale: Coagulation destabilizes suspended particles so they can

aggregate into larger flocs for easier removal in sedimentation and filtration. 1 / 4

• Which chemical is most commonly used for disinfection in public

water systems?

a) Ozone

b) Chlorine dioxide

c) Chlorine

d) Bromine

Answer: c) Chlorine

Rationale: Chlorine is widely used because it is effective, economical,

and provides a residual disinfectant throughout the distribution system.

• The maximum contaminant level (MCL) for nitrate as nitrogen (NO₃⁻-

N) in drinking water is:

• 5 mg/L
• 10 mg/L
• 20 mg/L
• 50 mg/L

Answer: b) 10 mg/L

Rationale: The EPA sets the MCL for nitrate at 10 mg/L to prevent

methemoglobinemia (“blue baby syndrome”) in infants.

• Which unit process follows coagulation in conventional water

treatment?

a) Flocculation

b) Sedimentation 2 / 4

c) Filtration

d) Disinfection

Answer: a) Flocculation

Rationale: Flocculation gently mixes water to encourage the formation

of larger flocs from coagulated particles.

• In water distribution, what is the primary purpose of a booster

chlorination system?

a) Increase water pressure

b) Reduce turbidity

c) Maintain residual disinfectant

d) Remove iron and manganese

Answer: c) Maintain residual disinfectant

Rationale: Booster chlorination ensures adequate chlorine levels

throughout the distribution system, preventing microbial regrowth.

• Which waterborne pathogen is a protozoan resistant to chlorine

disinfection?

a) Escherichia coli

b) Cryptosporidium

c) Giardia lamblia

d) Legionella

Answer: b) Cryptosporidium

Rationale: Cryptosporidium oocysts are highly resistant to chlorine and

require filtration or alternative disinfection methods. 3 / 4

7. The term “hard water” refers to water with high concentrations of:

a) Sodium and potassium

b) Calcium and magnesium

c) Iron and manganese

d) Chloride and sulfate

Answer: b) Calcium and magnesium

Rationale: Hardness is caused primarily by calcium and magnesium

ions, which can form scale in pipes and boilers.

• What is the primary function of a water meter in a distribution

system?

a) Measure water usage

b) Increase water pressure

c) Remove suspended solids

d) Provide disinfection

Answer: a) Measure water usage

Rationale: Meters quantify water consumption for billing and system

management purposes.

9. A water system’s hydraulic grade line (HGL) represents:

a) The pressure head at a point in the system

b) Flow velocity in pipes

c) Pump efficiency

d) Chlorine residual

Answer: a) The pressure head at a point in the system

• / 4