NYC DEP Drinking Water Treatment
Operator Grade One Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. What is the primary purpose of a drinking water treatment plant?
A. To increase water temperature
B. To remove contaminants and produce safe potable water
C. To generate electricity
D. To increase mineral content only
B. To remove contaminants and produce safe potable water
Rationale: The fundamental objective of a drinking water treatment plant
is to remove physical, chemical, and biological contaminants so that the
water is safe for human consumption.
2. Which federal law establishes national standards for public drinking
water systems?
A. Clean Air Act
B. Resource Conservation and Recovery Act
C. Safe Drinking Water Act
D. National Environmental Policy Act
,C. Safe Drinking Water Act
Rationale: The Safe Drinking Water Act authorizes the regulation of public
drinking water systems and establishes standards to protect public health.
3. What is turbidity?
A. Water temperature measurement
B. Water hardness measurement
C. Cloudiness caused by suspended particles
D. Chlorine concentration
C. Cloudiness caused by suspended particles
Rationale: Turbidity measures the presence of suspended solids that scatter
light and can interfere with disinfection processes.
4. Which treatment process is designed to destabilize suspended
particles?
A. Filtration
B. Coagulation
C. Disinfection
D. Aeration
B. Coagulation
Rationale: Coagulation neutralizes electrical charges on particles, allowing
them to combine into larger masses.
5. What is the primary purpose of flocculation?
A. Kill microorganisms
B. Increase pH
C. Form larger settleable particles
D. Remove chlorine
C. Form larger settleable particles
,Rationale: Flocculation gently mixes water so that destabilized particles
collide and form larger flocs that can be removed more easily.
6. Which process typically follows flocculation?
A. Sedimentation
B. Aeration
C. Chlorination
D. Fluoridation
A. Sedimentation
Rationale: After flocs form during flocculation, sedimentation allows
gravity to settle them out of the water.
7. What is the primary function of sedimentation?
A. Add oxygen
B. Remove dissolved minerals
C. Allow particles to settle by gravity
D. Adjust pH
C. Allow particles to settle by gravity
Rationale: Sedimentation removes suspended solids by allowing them to
settle to the bottom of a basin.
8. Why is filtration necessary after sedimentation?
A. To increase water pressure
B. To remove remaining suspended particles
C. To add disinfectants
D. To reduce water temperature
B. To remove remaining suspended particles
Rationale: Filtration captures fine particles that remain after
sedimentation, improving water clarity and quality.
, 9. Which filter medium is most commonly used in rapid sand filters?
A. Gravel only
B. Activated carbon only
C. Sand
D. Limestone
C. Sand
Rationale: Sand provides an effective medium for trapping particles while
allowing water to pass through efficiently.
10. What is the most commonly used disinfectant in drinking water
treatment?
A. Sulfuric acid
B. Chlorine
C. Sodium hydroxide
D. Lime
B. Chlorine
Rationale: Chlorine is widely used because it effectively kills pathogens and
provides a residual disinfectant in distribution systems.
11. What is chlorine residual?
A. Unused chlorine remaining in water after treatment
B. Chlorine removed by filtration
C. Chlorine added before treatment
D. Chlorine in raw water sources
A. Unused chlorine remaining in water after treatment
Rationale: Maintaining a chlorine residual helps protect water from
contamination as it moves through the distribution system.
Operator Grade One Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. What is the primary purpose of a drinking water treatment plant?
A. To increase water temperature
B. To remove contaminants and produce safe potable water
C. To generate electricity
D. To increase mineral content only
B. To remove contaminants and produce safe potable water
Rationale: The fundamental objective of a drinking water treatment plant
is to remove physical, chemical, and biological contaminants so that the
water is safe for human consumption.
2. Which federal law establishes national standards for public drinking
water systems?
A. Clean Air Act
B. Resource Conservation and Recovery Act
C. Safe Drinking Water Act
D. National Environmental Policy Act
,C. Safe Drinking Water Act
Rationale: The Safe Drinking Water Act authorizes the regulation of public
drinking water systems and establishes standards to protect public health.
3. What is turbidity?
A. Water temperature measurement
B. Water hardness measurement
C. Cloudiness caused by suspended particles
D. Chlorine concentration
C. Cloudiness caused by suspended particles
Rationale: Turbidity measures the presence of suspended solids that scatter
light and can interfere with disinfection processes.
4. Which treatment process is designed to destabilize suspended
particles?
A. Filtration
B. Coagulation
C. Disinfection
D. Aeration
B. Coagulation
Rationale: Coagulation neutralizes electrical charges on particles, allowing
them to combine into larger masses.
5. What is the primary purpose of flocculation?
A. Kill microorganisms
B. Increase pH
C. Form larger settleable particles
D. Remove chlorine
C. Form larger settleable particles
,Rationale: Flocculation gently mixes water so that destabilized particles
collide and form larger flocs that can be removed more easily.
6. Which process typically follows flocculation?
A. Sedimentation
B. Aeration
C. Chlorination
D. Fluoridation
A. Sedimentation
Rationale: After flocs form during flocculation, sedimentation allows
gravity to settle them out of the water.
7. What is the primary function of sedimentation?
A. Add oxygen
B. Remove dissolved minerals
C. Allow particles to settle by gravity
D. Adjust pH
C. Allow particles to settle by gravity
Rationale: Sedimentation removes suspended solids by allowing them to
settle to the bottom of a basin.
8. Why is filtration necessary after sedimentation?
A. To increase water pressure
B. To remove remaining suspended particles
C. To add disinfectants
D. To reduce water temperature
B. To remove remaining suspended particles
Rationale: Filtration captures fine particles that remain after
sedimentation, improving water clarity and quality.
, 9. Which filter medium is most commonly used in rapid sand filters?
A. Gravel only
B. Activated carbon only
C. Sand
D. Limestone
C. Sand
Rationale: Sand provides an effective medium for trapping particles while
allowing water to pass through efficiently.
10. What is the most commonly used disinfectant in drinking water
treatment?
A. Sulfuric acid
B. Chlorine
C. Sodium hydroxide
D. Lime
B. Chlorine
Rationale: Chlorine is widely used because it effectively kills pathogens and
provides a residual disinfectant in distribution systems.
11. What is chlorine residual?
A. Unused chlorine remaining in water after treatment
B. Chlorine removed by filtration
C. Chlorine added before treatment
D. Chlorine in raw water sources
A. Unused chlorine remaining in water after treatment
Rationale: Maintaining a chlorine residual helps protect water from
contamination as it moves through the distribution system.
