Master Plumber Licensing Exam Questions
With Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the minimum diameter for a residential water service
pipe?
A. ¾ inch
B. 1 inch
C. 1¼ inch
D. 1½ inch
The minimum diameter ensures adequate water flow and pressure
for residential use.
2. Which material is commonly used for underground water supply
piping?
A. PVC
B. CPVC
C. Copper Type K
D. Galvanized steel
Type K copper is durable and resistant to underground corrosion.
3. What is the maximum allowable lead content in potable water
pipes?
A. 5%
B. 0.25%
C. 1%
D. 2%
, Lead content must be minimal to meet safe drinking water
standards.
4. A trap primer is installed to:
A. Prevent backflow
B. Reduce water pressure
C. Maintain trap seal water level
D. Increase drainage speed
Trap primers prevent sewer gases from entering buildings by
keeping traps full of water.
5. Venting a plumbing system prevents:
A. Water hammer
B. Siphoning of traps
C. Hard water buildup
D. Pipe corrosion
Vents allow air in, preventing siphoning and maintaining proper
drainage.
6. What is the required slope for a 2-inch horizontal DWV pipe?
A. 1/16 inch per foot
B. ¼ inch per foot
C. ¼ inch per foot minimum
D. ½ inch per foot
Proper slope ensures gravity drains waste effectively.
7. What type of valve is typically installed on a water meter service
line?
A. Check valve
B. Ball valve
C. Gate valve
, D. Globe valve
Gate valves provide full shutoff without restricting flow.
8. What is the maximum distance a fixture can be from a vent?
A. 2 feet
B. 4 feet
C. 6 feet for 1½-inch pipe
D. 10 feet
Distance depends on pipe size to ensure proper venting.
9. Which is a common method for joining copper tubing?
A. Threading
B. Soldering (Sweating)
C. Welding
D. Compression only
Soldering ensures leak-free, durable connections for copper.
10. A backflow preventer is installed to:
A. Increase water pressure
B. Prevent contamination of potable water
C. Reduce flow velocity
D. Divert stormwater
It protects the public water supply from contamination.
11. Maximum allowable water velocity in residential piping is
generally:
A. 5 ft/s
B. 6 ft/s
C. 8 ft/s
D. 10 ft/s
Velocities above this can cause noise and erosion in pipes.
With Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the minimum diameter for a residential water service
pipe?
A. ¾ inch
B. 1 inch
C. 1¼ inch
D. 1½ inch
The minimum diameter ensures adequate water flow and pressure
for residential use.
2. Which material is commonly used for underground water supply
piping?
A. PVC
B. CPVC
C. Copper Type K
D. Galvanized steel
Type K copper is durable and resistant to underground corrosion.
3. What is the maximum allowable lead content in potable water
pipes?
A. 5%
B. 0.25%
C. 1%
D. 2%
, Lead content must be minimal to meet safe drinking water
standards.
4. A trap primer is installed to:
A. Prevent backflow
B. Reduce water pressure
C. Maintain trap seal water level
D. Increase drainage speed
Trap primers prevent sewer gases from entering buildings by
keeping traps full of water.
5. Venting a plumbing system prevents:
A. Water hammer
B. Siphoning of traps
C. Hard water buildup
D. Pipe corrosion
Vents allow air in, preventing siphoning and maintaining proper
drainage.
6. What is the required slope for a 2-inch horizontal DWV pipe?
A. 1/16 inch per foot
B. ¼ inch per foot
C. ¼ inch per foot minimum
D. ½ inch per foot
Proper slope ensures gravity drains waste effectively.
7. What type of valve is typically installed on a water meter service
line?
A. Check valve
B. Ball valve
C. Gate valve
, D. Globe valve
Gate valves provide full shutoff without restricting flow.
8. What is the maximum distance a fixture can be from a vent?
A. 2 feet
B. 4 feet
C. 6 feet for 1½-inch pipe
D. 10 feet
Distance depends on pipe size to ensure proper venting.
9. Which is a common method for joining copper tubing?
A. Threading
B. Soldering (Sweating)
C. Welding
D. Compression only
Soldering ensures leak-free, durable connections for copper.
10. A backflow preventer is installed to:
A. Increase water pressure
B. Prevent contamination of potable water
C. Reduce flow velocity
D. Divert stormwater
It protects the public water supply from contamination.
11. Maximum allowable water velocity in residential piping is
generally:
A. 5 ft/s
B. 6 ft/s
C. 8 ft/s
D. 10 ft/s
Velocities above this can cause noise and erosion in pipes.
