North Carolina Water Distribution System
Operator — Grade B Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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1. What is the primary purpose of a water distribution storage tank?
A. Provide electrical grounding
B. Reduce water hardness
C. Maintain system pressure and provide reserve supply
D. Remove sediment from drinking water
Storage tanks help maintain system pressure and ensure adequate
supply for peak demand and emergencies.
2. Which type of pipe is most commonly used for modern water
distribution mains?
A. Asbestos cement
B. PVC (Polyvinyl Chloride)
C. Lead
D. Aluminum
PVC is lightweight, corrosion-resistant, and widely used in distribution
systems.
3. A typical chlorine residual required at the farthest point in a
distribution system is:
,A. 0.02 mg/L
B. 2.0 mg/L
C. 0.2 mg/L
D. 5.0 mg/L
North Carolina rules generally require a detectable residual, commonly
around 0.2 mg/L free chlorine.
4. The term “head loss” refers to:
A. Water hammer
B. Loss of pressure due to friction in pipes
C. Loss of chlorine residual
D. Pump overheating
Friction between water and pipe walls reduces pressure as water flows.
5. The best way to prevent backflow is to:
A. Lower pump speed
B. Add more storage
C. Install and maintain proper backflow prevention devices
D. Increase main pressure
Backflow preventers protect potable water from contamination.
6. A service line typically runs from:
A. The well to the treatment plant
B. The water main to the customer’s meter
C. The tank to the booster station
D. The meter to the household plumbing
Service lines connect the distribution main to the customer connection
point.
7. What is the most common cause of water main breaks in winter?
, A. High chlorine residual
B. Freeze-thaw cycles causing ground movement
C. High water demand
D. Biofilm growth
Ground shifting due to freezing and thawing stresses pipes.
8. Unidirectional flushing is used primarily to:
A. Increase tank turnover
B. Measure water age
C. Remove sediment and improve water quality
D. Repair valves
This method creates high-velocity flow to scour mains.
9. When a hydrant is flushed, cloudy water is typically caused by:
A. Microbial contamination
B. Air entrainment
C. Chemical overfeed
D. Valve corrosion
High flow introduces air bubbles that make water appear milky.
10. A gate valve is best used for:
A. Throttling flow
B. Fully open or fully closed service
C. Pump speed control
D. Pressure monitoring
Gate valves are not designed for throttling.
11. The term “CT” for disinfection refers to:
Operator — Grade B Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a water distribution storage tank?
A. Provide electrical grounding
B. Reduce water hardness
C. Maintain system pressure and provide reserve supply
D. Remove sediment from drinking water
Storage tanks help maintain system pressure and ensure adequate
supply for peak demand and emergencies.
2. Which type of pipe is most commonly used for modern water
distribution mains?
A. Asbestos cement
B. PVC (Polyvinyl Chloride)
C. Lead
D. Aluminum
PVC is lightweight, corrosion-resistant, and widely used in distribution
systems.
3. A typical chlorine residual required at the farthest point in a
distribution system is:
,A. 0.02 mg/L
B. 2.0 mg/L
C. 0.2 mg/L
D. 5.0 mg/L
North Carolina rules generally require a detectable residual, commonly
around 0.2 mg/L free chlorine.
4. The term “head loss” refers to:
A. Water hammer
B. Loss of pressure due to friction in pipes
C. Loss of chlorine residual
D. Pump overheating
Friction between water and pipe walls reduces pressure as water flows.
5. The best way to prevent backflow is to:
A. Lower pump speed
B. Add more storage
C. Install and maintain proper backflow prevention devices
D. Increase main pressure
Backflow preventers protect potable water from contamination.
6. A service line typically runs from:
A. The well to the treatment plant
B. The water main to the customer’s meter
C. The tank to the booster station
D. The meter to the household plumbing
Service lines connect the distribution main to the customer connection
point.
7. What is the most common cause of water main breaks in winter?
, A. High chlorine residual
B. Freeze-thaw cycles causing ground movement
C. High water demand
D. Biofilm growth
Ground shifting due to freezing and thawing stresses pipes.
8. Unidirectional flushing is used primarily to:
A. Increase tank turnover
B. Measure water age
C. Remove sediment and improve water quality
D. Repair valves
This method creates high-velocity flow to scour mains.
9. When a hydrant is flushed, cloudy water is typically caused by:
A. Microbial contamination
B. Air entrainment
C. Chemical overfeed
D. Valve corrosion
High flow introduces air bubbles that make water appear milky.
10. A gate valve is best used for:
A. Throttling flow
B. Fully open or fully closed service
C. Pump speed control
D. Pressure monitoring
Gate valves are not designed for throttling.
11. The term “CT” for disinfection refers to:
