CO Master Plumber Exam Questions
And Correct Answers (Verified Answers)
Plus Rationale2026 Q&A| Instant
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1. Which type of pipe is commonly used for residential water supply due
to its corrosion resistance?
A. Cast iron
B. Galvanized steel
C. Copper
D. Concrete
Copper is highly resistant to corrosion and widely used in residential
plumbing.
2. The minimum slope for a 3-inch horizontal drainage pipe is:
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/8 to 1/4 inch per foot
D. 1/2 inch per foot
Drainage pipes must slope properly to ensure gravity flow and
prevent stagnation.
3. Which device is required to prevent backflow in potable water
systems?
A. Air gap
B. Check valve
C. Backflow preventer
D. Pressure reducing valve
A backflow preventer stops contaminated water from flowing back
into the potable supply.
4. What is the standard water pressure for residential plumbing systems?
A. 20–40 psi
, B. 30–50 psi
C. 40–60 psi
D. 60–80 psi
Residential systems are designed to operate efficiently within 40–60
psi.
5. Which fixture requires a trap to prevent sewer gases from entering the
building?
A. Water heater
B. Sink
C. Hose bibb
D. Expansion tank
Traps retain water to block sewer gases from entering occupied
spaces.
6. What is the maximum distance a fixture can be from a vent connection
on a 1 1/2-inch drain pipe?
A. 2 feet
B. 5 feet
C. 10 feet
D. 15 feet
Code specifies maximum distances for venting based on pipe size to
ensure proper air flow.
7. The main purpose of a vent in plumbing systems is to:
A. Increase water pressure
B. Drain wastewater faster
C. Prevent siphoning of traps
D. Filter water
Vents maintain atmospheric pressure and prevent traps from being
emptied by suction.
8. Which material is not suitable for hot water lines?
A. Copper
B. PEX
C. CPVC
D. PVC
PVC cannot handle hot water temperatures safely and is not
recommended for hot water supply.
9. The minimum size for a water service pipe to a residential building is:
A. 1/2 inch
, B. 3/4 inch
C. 1 inch
D. 2 inches
1-inch is generally required to provide adequate flow for a typical
residence.
10. What is the primary purpose of a pressure reducing valve?
A. Increase water pressure
B. Protect plumbing system from high pressure
C. Prevent backflow
D. Heat water
A pressure reducing valve lowers incoming high pressure to a safe
level for domestic plumbing.
11. Which type of joint is commonly used to join copper pipes?
A. Threaded
B. Flanged
C. Soldered (sweat)
D. Compression
Soldered joints provide a strong, watertight seal for copper piping.
12. How often should a building’s water heater be flushed?
A. Every month
B. Every 3 months
C. Annually
D. Every 5 years
Flushing prevents sediment buildup, extending the life and efficiency
of the water heater.
13. Which of the following is a common cause of low water
pressure?
A. Broken trap
B. Oversized pipe
C. Partially closed valve
D. Air vent
A partially closed valve restricts flow, reducing pressure at fixtures.
14. Which fixture unit value is assigned to a standard kitchen sink?
A. 0.5
B. 1
C. 1.5
D. 2
And Correct Answers (Verified Answers)
Plus Rationale2026 Q&A| Instant
Download Pdf
1. Which type of pipe is commonly used for residential water supply due
to its corrosion resistance?
A. Cast iron
B. Galvanized steel
C. Copper
D. Concrete
Copper is highly resistant to corrosion and widely used in residential
plumbing.
2. The minimum slope for a 3-inch horizontal drainage pipe is:
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/8 to 1/4 inch per foot
D. 1/2 inch per foot
Drainage pipes must slope properly to ensure gravity flow and
prevent stagnation.
3. Which device is required to prevent backflow in potable water
systems?
A. Air gap
B. Check valve
C. Backflow preventer
D. Pressure reducing valve
A backflow preventer stops contaminated water from flowing back
into the potable supply.
4. What is the standard water pressure for residential plumbing systems?
A. 20–40 psi
, B. 30–50 psi
C. 40–60 psi
D. 60–80 psi
Residential systems are designed to operate efficiently within 40–60
psi.
5. Which fixture requires a trap to prevent sewer gases from entering the
building?
A. Water heater
B. Sink
C. Hose bibb
D. Expansion tank
Traps retain water to block sewer gases from entering occupied
spaces.
6. What is the maximum distance a fixture can be from a vent connection
on a 1 1/2-inch drain pipe?
A. 2 feet
B. 5 feet
C. 10 feet
D. 15 feet
Code specifies maximum distances for venting based on pipe size to
ensure proper air flow.
7. The main purpose of a vent in plumbing systems is to:
A. Increase water pressure
B. Drain wastewater faster
C. Prevent siphoning of traps
D. Filter water
Vents maintain atmospheric pressure and prevent traps from being
emptied by suction.
8. Which material is not suitable for hot water lines?
A. Copper
B. PEX
C. CPVC
D. PVC
PVC cannot handle hot water temperatures safely and is not
recommended for hot water supply.
9. The minimum size for a water service pipe to a residential building is:
A. 1/2 inch
, B. 3/4 inch
C. 1 inch
D. 2 inches
1-inch is generally required to provide adequate flow for a typical
residence.
10. What is the primary purpose of a pressure reducing valve?
A. Increase water pressure
B. Protect plumbing system from high pressure
C. Prevent backflow
D. Heat water
A pressure reducing valve lowers incoming high pressure to a safe
level for domestic plumbing.
11. Which type of joint is commonly used to join copper pipes?
A. Threaded
B. Flanged
C. Soldered (sweat)
D. Compression
Soldered joints provide a strong, watertight seal for copper piping.
12. How often should a building’s water heater be flushed?
A. Every month
B. Every 3 months
C. Annually
D. Every 5 years
Flushing prevents sediment buildup, extending the life and efficiency
of the water heater.
13. Which of the following is a common cause of low water
pressure?
A. Broken trap
B. Oversized pipe
C. Partially closed valve
D. Air vent
A partially closed valve restricts flow, reducing pressure at fixtures.
14. Which fixture unit value is assigned to a standard kitchen sink?
A. 0.5
B. 1
C. 1.5
D. 2
