,This study document brings together 149 carefully worded exam questions drawn from TEXAS
WATER TREATMENT OPERATOR LICENSING EXAM WITH PRACTICE QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES Q&A, with the strongest
emphasis placed on Analyze source water quality and select appropriate treatment trains to meet
primary and secondary drinking water standards, Calculate chemical feed rates, filter loading rates,
CT values, and distribution system pressures under varying operational conditions, Diagnose and
troubleshoot unit process failures using jar test data, particle counts and and disinfection residual
trends. Every item follows the wording style and level of reasoning you meet in the real paper, and
each one is paired with a clear rationale so the correct choice is never a guess. Work through the
set at your own pace, mark the questions that slow you down, then come back to them until the
reasoning feels automatic. Learners who revise this way walk into the exam room recognising the
pattern behind the questions instead of meeting them for the first time. Keep going - steady, honest
practice is what turns a difficult paper into a comfortable pass.
Q1 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A surface water treatment plant uses alum coagulation at pH 6.5. Jar tests show
that increasing the alum dose from 20 mg/L to 30 mg/L improves turbidity removal
but drops filtered water pH to 6.0. Which adjustment best maintains optimal
coagulation while preventing lead and copper corrosion in the distribution
system?
A. Increase alum dose to 35 mg/L and add chlorine for oxidation.
B. Reduce alum dose to 15 mg/L and add a polymer as a coagulant aid.
C. Maintain 30 mg/L alum and add caustic soda to raise pH to 7.5 after filtration. CORRECT
D. Switch to ferric chloride at 25 mg/L without pH adjustment.
RATIONALE: Alum lowers pH; adding caustic after filtration restores pH to 7.5, minimizing
lead/copper solubility while preserving coagulation. Reducing alum may worsen turbidity, and
ferric chloride also lowers pH, increasing corrosion risk.
Page 2
,Q2 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A conventional rapid sand filter operates at 4 gpm/ft² with a media depth of 24
inches and effective size of 0.5 mm. After a backwash, the filter runs for 36 hours
before terminal head loss of 8 ft. If the operator increases the loading rate to 6
gpm/ft², which change in filter performance is most likely?
A. Longer filter runs due to increased scour of particles.
B. Shorter filter runs and increased risk of media loss. CORRECT
C. Improved particle removal efficiency due to deeper penetration.
D. No change in run time but higher backwash water use.
RATIONALE: Higher loading rates increase head loss development and shorten filter runs, while
also raising shear forces that can cause media loss. Particle removal may deteriorate, not
improve, due to reduced contact time.
Q3 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A groundwater system chlorinates with free chlorine at pH 8.2, 0.5 mg/L residual,
and 10°C. The system must achieve 4-log virus inactivation. According to the CT
table, the required CT is 6 mg-min/L. What is the minimum contact time (minutes)
in a baffled clearwell with a baffling factor of 0.7?
A. 17.1 minutes CORRECT
B. 12.0 minutes
C. 8.6 minutes
D. 24.0 minutes
RATIONALE: CT = residual × time × baffling factor. Rearranging: time = CT / (residual × baffling
factor) = 6 / (0.5 × 0.7) = 17.1 minutes. Other options miscalculate by omitting the baffling factor
or misplacing the decimal.
Page 3
, Q4 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A distribution system experiences a pressure drop to 15 psi during peak demand.
The system has a 12-inch main with a C-factor of 100. Which operational action is
most appropriate to restore pressure while maintaining chlorine residual?
A. Throttle a downstream valve to increase pressure upstream.
B. Increase pump speed and add booster chlorination at a strategic location. CORRECT
C. Flush hydrants to reduce stagnation.
D. Reduce storage tank overflow to maintain level.
RATIONALE: Increasing pump speed raises flow and pressure; booster chlorination maintains
residual in the affected area. Throttling valves would worsen pressure, flushing may lower
pressure further, and reducing overflow does not address demand.
Q5 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A treatment plant uses ozone for primary disinfection. Bromate formation is
detected at 12 µg/L, exceeding the MCL of 10 µg/L. Which operational change is
most effective at reducing bromate while maintaining disinfection?
A. Increase ozone dose and contact time.
B. Lower ozone dose, add hydrogen peroxide, and use chloramines for secondary disinfection.
CORRECT
C. Switch to free chlorine with a higher CT.
D. Add ammonia before ozonation to form bromamines.
RATIONALE: Lowering ozone dose and adding HO (advanced oxidation) can reduce bromate,
while chloramines provide a stable secondary residual. Increasing ozone would worsen bromate;
free chlorine may form brominated DBPs; adding ammonia before ozone can increase bromate.
Page 4
WATER TREATMENT OPERATOR LICENSING EXAM WITH PRACTICE QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES Q&A, with the strongest
emphasis placed on Analyze source water quality and select appropriate treatment trains to meet
primary and secondary drinking water standards, Calculate chemical feed rates, filter loading rates,
CT values, and distribution system pressures under varying operational conditions, Diagnose and
troubleshoot unit process failures using jar test data, particle counts and and disinfection residual
trends. Every item follows the wording style and level of reasoning you meet in the real paper, and
each one is paired with a clear rationale so the correct choice is never a guess. Work through the
set at your own pace, mark the questions that slow you down, then come back to them until the
reasoning feels automatic. Learners who revise this way walk into the exam room recognising the
pattern behind the questions instead of meeting them for the first time. Keep going - steady, honest
practice is what turns a difficult paper into a comfortable pass.
Q1 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A surface water treatment plant uses alum coagulation at pH 6.5. Jar tests show
that increasing the alum dose from 20 mg/L to 30 mg/L improves turbidity removal
but drops filtered water pH to 6.0. Which adjustment best maintains optimal
coagulation while preventing lead and copper corrosion in the distribution
system?
A. Increase alum dose to 35 mg/L and add chlorine for oxidation.
B. Reduce alum dose to 15 mg/L and add a polymer as a coagulant aid.
C. Maintain 30 mg/L alum and add caustic soda to raise pH to 7.5 after filtration. CORRECT
D. Switch to ferric chloride at 25 mg/L without pH adjustment.
RATIONALE: Alum lowers pH; adding caustic after filtration restores pH to 7.5, minimizing
lead/copper solubility while preserving coagulation. Reducing alum may worsen turbidity, and
ferric chloride also lowers pH, increasing corrosion risk.
Page 2
,Q2 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A conventional rapid sand filter operates at 4 gpm/ft² with a media depth of 24
inches and effective size of 0.5 mm. After a backwash, the filter runs for 36 hours
before terminal head loss of 8 ft. If the operator increases the loading rate to 6
gpm/ft², which change in filter performance is most likely?
A. Longer filter runs due to increased scour of particles.
B. Shorter filter runs and increased risk of media loss. CORRECT
C. Improved particle removal efficiency due to deeper penetration.
D. No change in run time but higher backwash water use.
RATIONALE: Higher loading rates increase head loss development and shorten filter runs, while
also raising shear forces that can cause media loss. Particle removal may deteriorate, not
improve, due to reduced contact time.
Q3 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A groundwater system chlorinates with free chlorine at pH 8.2, 0.5 mg/L residual,
and 10°C. The system must achieve 4-log virus inactivation. According to the CT
table, the required CT is 6 mg-min/L. What is the minimum contact time (minutes)
in a baffled clearwell with a baffling factor of 0.7?
A. 17.1 minutes CORRECT
B. 12.0 minutes
C. 8.6 minutes
D. 24.0 minutes
RATIONALE: CT = residual × time × baffling factor. Rearranging: time = CT / (residual × baffling
factor) = 6 / (0.5 × 0.7) = 17.1 minutes. Other options miscalculate by omitting the baffling factor
or misplacing the decimal.
Page 3
, Q4 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A distribution system experiences a pressure drop to 15 psi during peak demand.
The system has a 12-inch main with a C-factor of 100. Which operational action is
most appropriate to restore pressure while maintaining chlorine residual?
A. Throttle a downstream valve to increase pressure upstream.
B. Increase pump speed and add booster chlorination at a strategic location. CORRECT
C. Flush hydrants to reduce stagnation.
D. Reduce storage tank overflow to maintain level.
RATIONALE: Increasing pump speed raises flow and pressure; booster chlorination maintains
residual in the affected area. Throttling valves would worsen pressure, flushing may lower
pressure further, and reducing overflow does not address demand.
Q5 ANALYZE SOURCE WATER QUALITY AND SELECT APPROPRIATE TREATMENT TRAINS
TO MEET PRIMARY AND SECONDARY DRINKING WATER STANDARDS
A treatment plant uses ozone for primary disinfection. Bromate formation is
detected at 12 µg/L, exceeding the MCL of 10 µg/L. Which operational change is
most effective at reducing bromate while maintaining disinfection?
A. Increase ozone dose and contact time.
B. Lower ozone dose, add hydrogen peroxide, and use chloramines for secondary disinfection.
CORRECT
C. Switch to free chlorine with a higher CT.
D. Add ammonia before ozonation to form bromamines.
RATIONALE: Lowering ozone dose and adding HO (advanced oxidation) can reduce bromate,
while chloramines provide a stable secondary residual. Increasing ozone would worsen bromate;
free chlorine may form brominated DBPs; adding ammonia before ozone can increase bromate.
Page 4
