D2 Water Distribution Exam – Test Questions
with Correct Answers (2026/2027 Update)
1. What is the primary purpose of a water distribution system?
A) To treat raw water
B) To deliver potable water to consumers at adequate pressure and quantity
C) To store water for fire protection only
D) To collect wastewater
Answer B: To deliver potable water to consumers at adequate pressure and quantity
Rationale: Distribution systems deliver safe, potable water to homes, businesses, and fire hydrants at
sufficient pressure and flow.
2. What is the minimum recommended pressure in a water distribution system at customer service
connections?
A) 10 psi
B) 20 psi
C) 40 psi
D) 60 psi
Answer B: 20 psi
Rationale: Most regulatory agencies require a minimum of 20 psi at all points in the distribution system
under normal operating conditions.
3. Which type of pipe is most commonly used for water mains today?
A) Lead
B) Ductile iron
C) Asbestos cement
D) Wood
,Answer B: Ductile iron
Rationale: Ductile iron pipe is strong, durable, and resistant to corrosion when properly lined and
coated.
4. What is the primary function of a fire hydrant?
A) To drain the system
B) To provide water for firefighting
C) To measure flow
D) To regulate pressure
Answer B: To provide water for firefighting
Rationale: Fire hydrants provide a large volume of water for fire suppression and can also be used for
flushing and testing.
5. What is the purpose of a gate valve in a water distribution system?
A) To regulate flow
B) To isolate sections of the system for repair or maintenance
C) To prevent backflow
D) To measure pressure
Answer B: To isolate sections of the system for repair or maintenance
Rationale: Gate valves are used for on/off isolation, not throttling. They should be fully open or fully
closed.
6. What is the purpose of a butterfly valve?
A) To isolate flow only
B) To regulate or isolate flow
C) To prevent backflow
D) To measure flow
Answer B: To regulate or isolate flow
,Rationale: Butterfly valves can be used for throttling and isolation, but they cause more head loss than
gate valves.
7. What is the function of a check valve?
A) To isolate flow
B) To prevent backflow
C) To regulate pressure
D) To measure flow
Answer B: To prevent backflow
Rationale: Check valves allow flow in one direction only, preventing reverse flow that could contaminate
the system.
8. What is the purpose of a pressure reducing valve (PRV)?
A) To increase pressure
B) To reduce and maintain a consistent downstream pressure
C) To prevent backflow
D) To measure flow
Answer B: To reduce and maintain a consistent downstream pressure
Rationale: PRVs reduce high inlet pressure to a safe, consistent outlet pressure for consumers.
9. What is the most common cause of water main breaks?
A) Excessive pressure
B) Corrosion and aging infrastructure
C) Earthquakes
D) Freezing temperatures
Answer B: Corrosion and aging infrastructure
Rationale: Corrosion weakens pipe walls, and aging infrastructure is the leading cause of main breaks.
, 10. What is the purpose of thrust blocks?
A) To support pipes above ground
B) To counteract the forces at bends, tees, and reducers
C) To insulate pipes
D) To measure flow
Answer B: To counteract the forces at bends, tees, and reducers
Rationale: Thrust blocks are concrete structures that resist the hydraulic thrust at fittings, preventing
joint separation.
11. What is the proper method for disinfecting a new water main?
A) Flush with clean water only
B) Chlorination followed by flushing and bacteriological testing
C) Use only UV light
D) No disinfection is needed
Answer B: Chlorination followed by flushing and bacteriological testing
Rationale: New mains must be chlorinated, flushed, and tested for bacteria before being placed into
service.
12. What is the minimum chlorine residual required in a distribution system?
A) 0.1 mg/L
B) 0.2 mg/L
C) 0.5 mg/L
D) 1.0 mg/L
Answer B: 0.2 mg/L
Rationale: Most states require a minimum chlorine residual of 0.2 mg/L throughout the distribution
system.
with Correct Answers (2026/2027 Update)
1. What is the primary purpose of a water distribution system?
A) To treat raw water
B) To deliver potable water to consumers at adequate pressure and quantity
C) To store water for fire protection only
D) To collect wastewater
Answer B: To deliver potable water to consumers at adequate pressure and quantity
Rationale: Distribution systems deliver safe, potable water to homes, businesses, and fire hydrants at
sufficient pressure and flow.
2. What is the minimum recommended pressure in a water distribution system at customer service
connections?
A) 10 psi
B) 20 psi
C) 40 psi
D) 60 psi
Answer B: 20 psi
Rationale: Most regulatory agencies require a minimum of 20 psi at all points in the distribution system
under normal operating conditions.
3. Which type of pipe is most commonly used for water mains today?
A) Lead
B) Ductile iron
C) Asbestos cement
D) Wood
,Answer B: Ductile iron
Rationale: Ductile iron pipe is strong, durable, and resistant to corrosion when properly lined and
coated.
4. What is the primary function of a fire hydrant?
A) To drain the system
B) To provide water for firefighting
C) To measure flow
D) To regulate pressure
Answer B: To provide water for firefighting
Rationale: Fire hydrants provide a large volume of water for fire suppression and can also be used for
flushing and testing.
5. What is the purpose of a gate valve in a water distribution system?
A) To regulate flow
B) To isolate sections of the system for repair or maintenance
C) To prevent backflow
D) To measure pressure
Answer B: To isolate sections of the system for repair or maintenance
Rationale: Gate valves are used for on/off isolation, not throttling. They should be fully open or fully
closed.
6. What is the purpose of a butterfly valve?
A) To isolate flow only
B) To regulate or isolate flow
C) To prevent backflow
D) To measure flow
Answer B: To regulate or isolate flow
,Rationale: Butterfly valves can be used for throttling and isolation, but they cause more head loss than
gate valves.
7. What is the function of a check valve?
A) To isolate flow
B) To prevent backflow
C) To regulate pressure
D) To measure flow
Answer B: To prevent backflow
Rationale: Check valves allow flow in one direction only, preventing reverse flow that could contaminate
the system.
8. What is the purpose of a pressure reducing valve (PRV)?
A) To increase pressure
B) To reduce and maintain a consistent downstream pressure
C) To prevent backflow
D) To measure flow
Answer B: To reduce and maintain a consistent downstream pressure
Rationale: PRVs reduce high inlet pressure to a safe, consistent outlet pressure for consumers.
9. What is the most common cause of water main breaks?
A) Excessive pressure
B) Corrosion and aging infrastructure
C) Earthquakes
D) Freezing temperatures
Answer B: Corrosion and aging infrastructure
Rationale: Corrosion weakens pipe walls, and aging infrastructure is the leading cause of main breaks.
, 10. What is the purpose of thrust blocks?
A) To support pipes above ground
B) To counteract the forces at bends, tees, and reducers
C) To insulate pipes
D) To measure flow
Answer B: To counteract the forces at bends, tees, and reducers
Rationale: Thrust blocks are concrete structures that resist the hydraulic thrust at fittings, preventing
joint separation.
11. What is the proper method for disinfecting a new water main?
A) Flush with clean water only
B) Chlorination followed by flushing and bacteriological testing
C) Use only UV light
D) No disinfection is needed
Answer B: Chlorination followed by flushing and bacteriological testing
Rationale: New mains must be chlorinated, flushed, and tested for bacteria before being placed into
service.
12. What is the minimum chlorine residual required in a distribution system?
A) 0.1 mg/L
B) 0.2 mg/L
C) 0.5 mg/L
D) 1.0 mg/L
Answer B: 0.2 mg/L
Rationale: Most states require a minimum chlorine residual of 0.2 mg/L throughout the distribution
system.
