Texas Water Class D Operator License Exam | TCEQ Practice
QUESTIONs, Correct Answers & Detailed Rationales
(2026/2027)
QUESTION 1 What is the regulatory definition of a Public Water System
(PWS) in Texas?
• A. A system that provides water to at least 15 service connections
or serves at least 25 individuals at least 60 days a year.
• B. A system that provides water to at least 5 service connections.
• C. Any system that sells water to more than 10 households.
• D. A system that uses surface water.
Correct Answer: A. A system that provides water to at least 15 service
connections or serves at least 25 individuals at least 60 days a year.
Detailed Rationale: According to TCEQ rules (30 TAC §290.38), this is
the threshold for a system to be regulated as a public water system in
Texas.
QUESTION 2 What is the primary purpose of disinfection in a public
water system?
• A. To remove all dissolved minerals.
• B. To eliminate taste and odor problems.
• C. To destroy pathogenic microorganisms.
• D. To prevent the water from freezing.
,Correct Answer: C. To destroy pathogenic microorganisms.
Detailed Rationale: Disinfection (usually via chlorine) is the most critical
step in water treatment to ensure the water is safe for human
consumption by killing bacteria, viruses, and protozoa.
QUESTION 3 What is the minimum chlorine residual required
throughout the distribution system in Texas?
• A. 0.0 mg/L
• B. 0.2 mg/L
• C. 0.5 mg/L
• D. 1.0 mg/L
Correct Answer: B. 0.2 mg/L
Detailed Rationale: TCEQ Chapter 290 requires a minimum free
chlorine residual of 0.2 mg/L (or 0.5 mg/L for chloramines) at all times
in the distribution system to ensure continuous protection against
contamination.
QUESTION 4 What is the main purpose of routine coliform sampling?
• A. To detect chemical contaminants like lead.
• B. To determine the hardness of the water.
• C. To act as an indicator of potential microbial contamination.
• D. To measure the chlorine residual.
Correct Answer: C. To act as an indicator of potential microbial
contamination.
,Detailed Rationale: Coliform bacteria are used as "indicator organisms."
If they are present, it suggests that other, more harmful pathogens
might also be present in the water supply.
QUESTION 5 What is the required minimum sanitary control easement
distance for a public water well in Texas?
• A. 50 feet
• B. 100 feet
• C. 150 feet
• D. 500 feet
Correct Answer: C. 150 feet
Detailed Rationale: TCEQ regulations generally require a 150-foot
sanitary control easement around a wellhead to prevent contamination
from septic tanks, chemical storage, or other sources.
QUESTION 6 What should an operator do if they suspect a cross-
connection in the water system?
• A. Wait until the next routine inspection to check it.
• B. Immediately isolate the area and take steps to eliminate the
cross-connection.
• C. Increase the chlorine dosage.
• D. Notify the mayor only.
Correct Answer: B. Immediately isolate the area and take steps to
eliminate the cross-connection.
, Detailed Rationale: A cross-connection creates a path for contaminants
to enter the drinking water. Immediate action is required to protect
public health.
QUESTION 7 Which of the following is a symptom of water system
contamination?
• A. Clear, odorless water.
• B. Unexplained turbidity, color, or a change in taste/odor.
• C. Lower than normal water pressure.
• D. Consistent flow rates.
Correct Answer: B. Unexplained turbidity, color, or a change in
taste/odor.
Detailed Rationale: Physical changes in water quality are often the first
sign of a potential distribution system problem or contamination event.
QUESTION 8 What is the function of an air relief valve on a water line?
• A. To allow air to escape from the line when filling and prevent air
pockets.
• B. To increase water pressure.
• C. To add chlorine to the water.
• D. To measure water flow.
Correct Answer: A. To allow air to escape from the line when filling and
prevent air pockets.
Detailed Rationale: Air pockets can cause "air binding" in pipes and
interfere with flow, as well as lead to pressure surges.
QUESTIONs, Correct Answers & Detailed Rationales
(2026/2027)
QUESTION 1 What is the regulatory definition of a Public Water System
(PWS) in Texas?
• A. A system that provides water to at least 15 service connections
or serves at least 25 individuals at least 60 days a year.
• B. A system that provides water to at least 5 service connections.
• C. Any system that sells water to more than 10 households.
• D. A system that uses surface water.
Correct Answer: A. A system that provides water to at least 15 service
connections or serves at least 25 individuals at least 60 days a year.
Detailed Rationale: According to TCEQ rules (30 TAC §290.38), this is
the threshold for a system to be regulated as a public water system in
Texas.
QUESTION 2 What is the primary purpose of disinfection in a public
water system?
• A. To remove all dissolved minerals.
• B. To eliminate taste and odor problems.
• C. To destroy pathogenic microorganisms.
• D. To prevent the water from freezing.
,Correct Answer: C. To destroy pathogenic microorganisms.
Detailed Rationale: Disinfection (usually via chlorine) is the most critical
step in water treatment to ensure the water is safe for human
consumption by killing bacteria, viruses, and protozoa.
QUESTION 3 What is the minimum chlorine residual required
throughout the distribution system in Texas?
• A. 0.0 mg/L
• B. 0.2 mg/L
• C. 0.5 mg/L
• D. 1.0 mg/L
Correct Answer: B. 0.2 mg/L
Detailed Rationale: TCEQ Chapter 290 requires a minimum free
chlorine residual of 0.2 mg/L (or 0.5 mg/L for chloramines) at all times
in the distribution system to ensure continuous protection against
contamination.
QUESTION 4 What is the main purpose of routine coliform sampling?
• A. To detect chemical contaminants like lead.
• B. To determine the hardness of the water.
• C. To act as an indicator of potential microbial contamination.
• D. To measure the chlorine residual.
Correct Answer: C. To act as an indicator of potential microbial
contamination.
,Detailed Rationale: Coliform bacteria are used as "indicator organisms."
If they are present, it suggests that other, more harmful pathogens
might also be present in the water supply.
QUESTION 5 What is the required minimum sanitary control easement
distance for a public water well in Texas?
• A. 50 feet
• B. 100 feet
• C. 150 feet
• D. 500 feet
Correct Answer: C. 150 feet
Detailed Rationale: TCEQ regulations generally require a 150-foot
sanitary control easement around a wellhead to prevent contamination
from septic tanks, chemical storage, or other sources.
QUESTION 6 What should an operator do if they suspect a cross-
connection in the water system?
• A. Wait until the next routine inspection to check it.
• B. Immediately isolate the area and take steps to eliminate the
cross-connection.
• C. Increase the chlorine dosage.
• D. Notify the mayor only.
Correct Answer: B. Immediately isolate the area and take steps to
eliminate the cross-connection.
, Detailed Rationale: A cross-connection creates a path for contaminants
to enter the drinking water. Immediate action is required to protect
public health.
QUESTION 7 Which of the following is a symptom of water system
contamination?
• A. Clear, odorless water.
• B. Unexplained turbidity, color, or a change in taste/odor.
• C. Lower than normal water pressure.
• D. Consistent flow rates.
Correct Answer: B. Unexplained turbidity, color, or a change in
taste/odor.
Detailed Rationale: Physical changes in water quality are often the first
sign of a potential distribution system problem or contamination event.
QUESTION 8 What is the function of an air relief valve on a water line?
• A. To allow air to escape from the line when filling and prevent air
pockets.
• B. To increase water pressure.
• C. To add chlorine to the water.
• D. To measure water flow.
Correct Answer: A. To allow air to escape from the line when filling and
prevent air pockets.
Detailed Rationale: Air pockets can cause "air binding" in pipes and
interfere with flow, as well as lead to pressure surges.
