TEXAS CLASS D WATER LICENSE EXAM ACTUAL EXAM 2026/2027
- 100% VERIFIED QUESTIONS WITH COMPLETE ANSWERS
DETAILED RATIONALES - PASS GUARANTEED - A+ GRADED
160 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Apply principles of water chemistry, hydraulics, and treatment processes to operational scenarios
2 Evaluate regulatory requirements and implement compliance strategies for safe drinking water
3 Analyze system performance and troubleshoot operational issues to ensure water quality and public
health
4 Texas Class D Water License Exam Actual Exam 2026
5 2027
6 100% Verified Questions with Complete Answers Detailed Rationales
7 Pass Guaranteed
8 A+ Graded
9 Foundations of Water Treatment and Distribution Operations
10 Applied Water Treatment and Distribution Operations
11 Advanced Water Treatment and Distribution Operations
12 Water Treatment and Distribution Operations Review
Page 1
,Q1 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water treatment plant using surface water has a raw water turbidity of 12 NTU
and a pH of 8.5. The operator adds alum at a dose of 15 mg/L. The flocculation
basin is designed for a velocity gradient (G) of 40 s^-1 and a detention time of 30
minutes. Which adjustment is most appropriate to optimize
coagulation-flocculation?
A. Increase alum dose to 25 mg/L and add lime to lower pH to 7.0 CORRECT
B. Decrease alum dose to 10 mg/L and add soda ash to raise pH to 9.0
C. Maintain current dose but increase the flocculation G to 80 s^-1
D. Maintain current dose but reduce flocculation detention time to 15 minutes
RATIONALE: Alum coagulation is most effective in the pH range of 5.5-7.5 for surface waters.
The raw pH of 8.5 is above optimal, so adding lime to lower pH and increasing alum dose to
compensate for higher turbidity is appropriate. Option B is wrong because raising pH further is
counterproductive. Options C and D do not address the pH issue and could break flocs.
Q2 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water utility experiences a sudden drop in chlorine residual at a remote point in
the distribution system while the chlorine feed rate remains constant. The operator
checks the SCADA data and finds that water demand has increased. What is the
most likely cause of the residual drop?
A. Increased water age due to lower turnover
B. Higher chlorine demand from increased organic matter CORRECT
C. Decreased chlorine decay rate due to higher temperature
D. Formation of disinfection byproducts (DBPs) reducing chlorine
RATIONALE: Increased water demand can resuspend sediments and biofilms, introducing
organic matter that exerts chlorine demand, consuming the residual. Option A is the
opposite-higher demand reduces water age. Option C is wrong because higher temperature
increases decay, not decreases. Option D is a consequence of chlorine reacting with organics
but not the primary cause.
Page 2
,Q3 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
An operator is tasked with selecting a pipe material for a new 6-inch water main
that will be installed in a highly corrosive soil with a high water table. Which pipe
material is most appropriate?
A. Ductile iron with polyethylene encasement CORRECT
B. Unlined cast iron
C. Concrete cylinder pipe
D. Galvanized steel
RATIONALE: Ductile iron with polyethylene encasement provides corrosion protection in
aggressive soils. Unlined cast iron and galvanized steel are prone to corrosion. Concrete cylinder
pipe is typically used for large transmission mains, not small distribution lines, and may be
affected by acidic soils.
Q4 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water system has a total trihalomethane (TTHM) concentration of 0.090 mg/L,
which is above the MCL of 0.080 mg/L. The system uses chlorine as a disinfectant.
Which of the following strategies would be most effective in reducing TTHM
formation?
A. Increase chlorine dose to maintain higher residual
B. Switch to chloramination as the primary disinfectant CORRECT
C. Reduce pH to 6.5
D. Increase water temperature in the distribution system
RATIONALE: Chloramines produce significantly fewer THMs than free chlorine because they do
not react as readily with organic precursors. Option A would increase DBP formation. Option C
might slightly reduce THM formation but not as effectively as switching disinfectants. Option D
would increase reaction rates and THM formation.
Page 3
, Q5 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water storage tank is being inspected and the operator finds a layer of sediment
on the floor. The tank is 100 feet in diameter and the sediment depth averages 2
inches. What is the approximate volume of sediment in the tank?
A. 1,300 cubic feet CORRECT
B. 1,800 cubic feet
C. 2,600 cubic feet
D. 3,900 cubic feet
RATIONALE: Volume = area × depth. Area = × (diameter/2)^2 = 3.1416 × 50^2 = 7,854 sq ft.
Depth = 2 inches = 0.167 ft. Volume = 7,854 × 0.167 1,312 cubic feet, which rounds to about
1,300 cubic feet. The other options are incorrect calculations.
Q6 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
During a routine inspection of a water treatment plant, the operator notices that
the pressure drop across a rapid sand filter has increased from 2 psi to 8 psi over
a period of 24 hours. The filter is producing clear water. What is the most
appropriate action?
A. Continue operation until turbidity breakthrough occurs
B. Backwash the filter immediately CORRECT
C. Increase filtration rate to compensate for head loss
D. Reduce coagulant dose to decrease floc carryover
RATIONALE: A rapid increase in head loss indicates filter clogging. Backwashing is necessary to
remove accumulated solids and prevent channeling or breakthrough. Continuing operation risks
turbidity breakthrough. Increasing filtration rate would worsen the problem. Reducing coagulant
dose could compromise water quality.
Page 4
- 100% VERIFIED QUESTIONS WITH COMPLETE ANSWERS
DETAILED RATIONALES - PASS GUARANTEED - A+ GRADED
160 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Apply principles of water chemistry, hydraulics, and treatment processes to operational scenarios
2 Evaluate regulatory requirements and implement compliance strategies for safe drinking water
3 Analyze system performance and troubleshoot operational issues to ensure water quality and public
health
4 Texas Class D Water License Exam Actual Exam 2026
5 2027
6 100% Verified Questions with Complete Answers Detailed Rationales
7 Pass Guaranteed
8 A+ Graded
9 Foundations of Water Treatment and Distribution Operations
10 Applied Water Treatment and Distribution Operations
11 Advanced Water Treatment and Distribution Operations
12 Water Treatment and Distribution Operations Review
Page 1
,Q1 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water treatment plant using surface water has a raw water turbidity of 12 NTU
and a pH of 8.5. The operator adds alum at a dose of 15 mg/L. The flocculation
basin is designed for a velocity gradient (G) of 40 s^-1 and a detention time of 30
minutes. Which adjustment is most appropriate to optimize
coagulation-flocculation?
A. Increase alum dose to 25 mg/L and add lime to lower pH to 7.0 CORRECT
B. Decrease alum dose to 10 mg/L and add soda ash to raise pH to 9.0
C. Maintain current dose but increase the flocculation G to 80 s^-1
D. Maintain current dose but reduce flocculation detention time to 15 minutes
RATIONALE: Alum coagulation is most effective in the pH range of 5.5-7.5 for surface waters.
The raw pH of 8.5 is above optimal, so adding lime to lower pH and increasing alum dose to
compensate for higher turbidity is appropriate. Option B is wrong because raising pH further is
counterproductive. Options C and D do not address the pH issue and could break flocs.
Q2 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water utility experiences a sudden drop in chlorine residual at a remote point in
the distribution system while the chlorine feed rate remains constant. The operator
checks the SCADA data and finds that water demand has increased. What is the
most likely cause of the residual drop?
A. Increased water age due to lower turnover
B. Higher chlorine demand from increased organic matter CORRECT
C. Decreased chlorine decay rate due to higher temperature
D. Formation of disinfection byproducts (DBPs) reducing chlorine
RATIONALE: Increased water demand can resuspend sediments and biofilms, introducing
organic matter that exerts chlorine demand, consuming the residual. Option A is the
opposite-higher demand reduces water age. Option C is wrong because higher temperature
increases decay, not decreases. Option D is a consequence of chlorine reacting with organics
but not the primary cause.
Page 2
,Q3 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
An operator is tasked with selecting a pipe material for a new 6-inch water main
that will be installed in a highly corrosive soil with a high water table. Which pipe
material is most appropriate?
A. Ductile iron with polyethylene encasement CORRECT
B. Unlined cast iron
C. Concrete cylinder pipe
D. Galvanized steel
RATIONALE: Ductile iron with polyethylene encasement provides corrosion protection in
aggressive soils. Unlined cast iron and galvanized steel are prone to corrosion. Concrete cylinder
pipe is typically used for large transmission mains, not small distribution lines, and may be
affected by acidic soils.
Q4 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water system has a total trihalomethane (TTHM) concentration of 0.090 mg/L,
which is above the MCL of 0.080 mg/L. The system uses chlorine as a disinfectant.
Which of the following strategies would be most effective in reducing TTHM
formation?
A. Increase chlorine dose to maintain higher residual
B. Switch to chloramination as the primary disinfectant CORRECT
C. Reduce pH to 6.5
D. Increase water temperature in the distribution system
RATIONALE: Chloramines produce significantly fewer THMs than free chlorine because they do
not react as readily with organic precursors. Option A would increase DBP formation. Option C
might slightly reduce THM formation but not as effectively as switching disinfectants. Option D
would increase reaction rates and THM formation.
Page 3
, Q5 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
A water storage tank is being inspected and the operator finds a layer of sediment
on the floor. The tank is 100 feet in diameter and the sediment depth averages 2
inches. What is the approximate volume of sediment in the tank?
A. 1,300 cubic feet CORRECT
B. 1,800 cubic feet
C. 2,600 cubic feet
D. 3,900 cubic feet
RATIONALE: Volume = area × depth. Area = × (diameter/2)^2 = 3.1416 × 50^2 = 7,854 sq ft.
Depth = 2 inches = 0.167 ft. Volume = 7,854 × 0.167 1,312 cubic feet, which rounds to about
1,300 cubic feet. The other options are incorrect calculations.
Q6 APPLY PRINCIPLES OF WATER CHEMISTRY, HYDRAULICS, AND TREATMENT
PROCESSES TO OPERATIONAL SCENARIOS
During a routine inspection of a water treatment plant, the operator notices that
the pressure drop across a rapid sand filter has increased from 2 psi to 8 psi over
a period of 24 hours. The filter is producing clear water. What is the most
appropriate action?
A. Continue operation until turbidity breakthrough occurs
B. Backwash the filter immediately CORRECT
C. Increase filtration rate to compensate for head loss
D. Reduce coagulant dose to decrease floc carryover
RATIONALE: A rapid increase in head loss indicates filter clogging. Backwashing is necessary to
remove accumulated solids and prevent channeling or breakthrough. Continuing operation risks
turbidity breakthrough. Increasing filtration rate would worsen the problem. Reducing coagulant
dose could compromise water quality.
Page 4
