Texas Water Class C Distribution Operator Exam | TCEQ
Complete Practice QUESTIONs & Detailed Rationales
(2026/2027)
QUESTION 1 What is the head pressure in feet of water if the gauge
reads 50 psi?
• A. 115.5 feet
• B. 21.6 feet
• C. 23.1 feet
• D. 50.0 feet
Correct Answer: A. 115.5 feet
Detailed Rationale: The standard conversion factor is 1 psi = 2.31 feet
of head. 50 psi × 2.31 = 115.5 feet. This is a fundamental hydraulic
calculation for Class C operators.
QUESTION 2 When installing a new water main, what is the primary
purpose of a hydrostatic pressure test?
• A. To check if the pipe is the correct color.
• B. To ensure the pipe can withstand operating pressures and verify
the integrity of joints and fittings.
• C. To flush the pipe of construction debris.
• D. To verify the flow rate capacity of the main.
,Correct Answer: B. To ensure the pipe can withstand operating
pressures and verify the integrity of joints and fittings.
Detailed Rationale: Hydrostatic testing involves pressurizing the line
(usually to 1.5 times the operating pressure) to ensure there are no
leaks before the line is put into service.
QUESTION 3 What is "cavitation" in a centrifugal pump?
• A. The sound of a pump operating at peak efficiency.
• B. The formation and collapse of vapor bubbles on the impeller,
which can cause severe damage.
• C. The process of adding air to the water to improve taste.
• D. A method of cleaning the pump volute.
Correct Answer: B. The formation and collapse of vapor bubbles on the
impeller, which can cause severe damage.
Detailed Rationale: Cavitation occurs when the suction pressure drops
below the vapor pressure of the water. It sounds like marbles in the
pump and can erode the impeller metal quickly.
QUESTION 4 Which type of backflow prevention assembly is required
for a high-hazard cross-connection?
• A. Double Check Valve Assembly (DCVA).
• B. Reduced Pressure Zone (RPZ) Assembly.
• C. Pressure Vacuum Breaker (PVB).
• D. Atmospheric Vacuum Breaker.
Correct Answer: B. Reduced Pressure Zone (RPZ) Assembly.
,Detailed Rationale: An RPZ is the only mechanical assembly listed that
is suitable for high-hazard cross-connections because it includes a relief
valve to dump water if the check valves fail.
QUESTION 5 According to OSHA, at what trench depth must an
excavation be protected by a protective system (shoring, sloping, or
shielding)?
• A. 3 feet or deeper.
• B. 5 feet or deeper.
• C. 8 feet or deeper.
• D. 10 feet or deeper.
Correct Answer: B. 5 feet or deeper.
Detailed Rationale: OSHA 1926 Subpart P requires that any excavation
5 feet or deeper must have cave-in protection. Excavations 4 feet or
deeper also require a means of egress (ladders).
QUESTION 6 What is the minimum pressure a water system must
maintain in the distribution system under normal operating conditions?
• A. 10 psi.
• B. 20 psi.
• C. 35 psi.
• D. 50 psi.
Correct Answer: B. 20 psi.
, Detailed Rationale: TCEQ rules require a minimum of 20 psi at all
service connections. Dropping below 20 psi creates a risk of back-
siphonage and requires a boil water notice.
QUESTION 7 What is "breakpoint chlorination"?
• A. The point where all chlorine is gone.
• B. Adding enough chlorine to satisfy the chlorine demand and
leave a free chlorine residual.
• C. The point where the water freezes.
• D. Adding chlorine until the pH drops.
Correct Answer: B. Adding enough chlorine to satisfy the chlorine
demand and leave a free chlorine residual.
Detailed Rationale: You must add enough chlorine to "break through"
the combined chlorine stage (where chlorine reacts with ammonia) to
ensure a stable free chlorine residual for disinfection.
QUESTION 8 What is the primary cause of tuberculation in unlined cast
iron pipes?
• A. High water pressure.
• B. Corrosion and the formation of iron oxide nodules on the pipe
interior.
• C. Low flow velocities.
• D. Excess fluoride in the water.
Correct Answer: B. Corrosion and the formation of iron oxide nodules
on the pipe interior.
Complete Practice QUESTIONs & Detailed Rationales
(2026/2027)
QUESTION 1 What is the head pressure in feet of water if the gauge
reads 50 psi?
• A. 115.5 feet
• B. 21.6 feet
• C. 23.1 feet
• D. 50.0 feet
Correct Answer: A. 115.5 feet
Detailed Rationale: The standard conversion factor is 1 psi = 2.31 feet
of head. 50 psi × 2.31 = 115.5 feet. This is a fundamental hydraulic
calculation for Class C operators.
QUESTION 2 When installing a new water main, what is the primary
purpose of a hydrostatic pressure test?
• A. To check if the pipe is the correct color.
• B. To ensure the pipe can withstand operating pressures and verify
the integrity of joints and fittings.
• C. To flush the pipe of construction debris.
• D. To verify the flow rate capacity of the main.
,Correct Answer: B. To ensure the pipe can withstand operating
pressures and verify the integrity of joints and fittings.
Detailed Rationale: Hydrostatic testing involves pressurizing the line
(usually to 1.5 times the operating pressure) to ensure there are no
leaks before the line is put into service.
QUESTION 3 What is "cavitation" in a centrifugal pump?
• A. The sound of a pump operating at peak efficiency.
• B. The formation and collapse of vapor bubbles on the impeller,
which can cause severe damage.
• C. The process of adding air to the water to improve taste.
• D. A method of cleaning the pump volute.
Correct Answer: B. The formation and collapse of vapor bubbles on the
impeller, which can cause severe damage.
Detailed Rationale: Cavitation occurs when the suction pressure drops
below the vapor pressure of the water. It sounds like marbles in the
pump and can erode the impeller metal quickly.
QUESTION 4 Which type of backflow prevention assembly is required
for a high-hazard cross-connection?
• A. Double Check Valve Assembly (DCVA).
• B. Reduced Pressure Zone (RPZ) Assembly.
• C. Pressure Vacuum Breaker (PVB).
• D. Atmospheric Vacuum Breaker.
Correct Answer: B. Reduced Pressure Zone (RPZ) Assembly.
,Detailed Rationale: An RPZ is the only mechanical assembly listed that
is suitable for high-hazard cross-connections because it includes a relief
valve to dump water if the check valves fail.
QUESTION 5 According to OSHA, at what trench depth must an
excavation be protected by a protective system (shoring, sloping, or
shielding)?
• A. 3 feet or deeper.
• B. 5 feet or deeper.
• C. 8 feet or deeper.
• D. 10 feet or deeper.
Correct Answer: B. 5 feet or deeper.
Detailed Rationale: OSHA 1926 Subpart P requires that any excavation
5 feet or deeper must have cave-in protection. Excavations 4 feet or
deeper also require a means of egress (ladders).
QUESTION 6 What is the minimum pressure a water system must
maintain in the distribution system under normal operating conditions?
• A. 10 psi.
• B. 20 psi.
• C. 35 psi.
• D. 50 psi.
Correct Answer: B. 20 psi.
, Detailed Rationale: TCEQ rules require a minimum of 20 psi at all
service connections. Dropping below 20 psi creates a risk of back-
siphonage and requires a boil water notice.
QUESTION 7 What is "breakpoint chlorination"?
• A. The point where all chlorine is gone.
• B. Adding enough chlorine to satisfy the chlorine demand and
leave a free chlorine residual.
• C. The point where the water freezes.
• D. Adding chlorine until the pH drops.
Correct Answer: B. Adding enough chlorine to satisfy the chlorine
demand and leave a free chlorine residual.
Detailed Rationale: You must add enough chlorine to "break through"
the combined chlorine stage (where chlorine reacts with ammonia) to
ensure a stable free chlorine residual for disinfection.
QUESTION 8 What is the primary cause of tuberculation in unlined cast
iron pipes?
• A. High water pressure.
• B. Corrosion and the formation of iron oxide nodules on the pipe
interior.
• C. Low flow velocities.
• D. Excess fluoride in the water.
Correct Answer: B. Corrosion and the formation of iron oxide nodules
on the pipe interior.
