Class B Water Operator Certification Practice Exam |
Comprehensive Study Guide with Actual Exam Questions,
Verified Correct Answers and Detailed Rationales | Latest
Update -2026/2027
Question 1
Theoretically it takes ______ of chlorine to oxidize 1 mg/L of hydrogen sulfide to the sulfate
form.
A. 6.24 mg/L
B. 4.16 mg/L
C. 12.48 mg/L
D. 8.32 mg/L
Answer: D
Rationale: The theoretical chlorine demand for oxidizing hydrogen sulfide to sulfate is 8.32
mg/L of chlorine per 1 mg/L of H₂S.
Question 2
The polymer most frequently found to be effective in the collection and removal of particles
from water is a:
A. Low molecular weight, anionic polymer
B. Medium molecular weight, non-ionic polymer
C. High molecular weight, amphoteric polymer
D. High molecular weight, cationic polymer
Answer: D
Rationale: High molecular weight cationic polymers are most effective as coagulant aids
because they neutralize the negative charge of particles and promote floc formation.
Question 3
Recarbonation is necessary after lime softening in order to:
A. Reduce the scale forming tendencies of supersaturated water
B. Increase the pH to enhance disinfection
C. Reduce the turbidity of the water
D. Stabilize the chlorine levels in the water
Answer: A
pg. 1
,Rationale: Recarbonation adds carbon dioxide to reduce the pH and stabilize the water,
preventing calcium carbonate scale formation in the distribution system.
Question 4
Mud ball evaluation indicates a sample to be 2.5% to 5%. This is considered to be:
A. Good
B. Normal
C. Great
D. Bad
Answer: B
Rationale: A mud ball content of 2.5% to 5% is considered normal. Higher percentages indicate
poor backwashing and media problems.
Question 5
The metabolic process that consumes oxygen and releases carbon dioxide is:
A. Transpiration
B. Photosynthesis
C. Oxidation
D. Respiration
Answer: D
Rationale: Respiration is the metabolic process where organisms consume oxygen and release
carbon dioxide. Photosynthesis does the opposite.
Question 6
To stop slum floc from carrying over into the launders:
A. Remove turbidity
B. Detention is not critical in the flocculation process
C. Add or start polymer
D. Floc to prematurely settle out
Answer: C
Rationale: Adding or starting polymer helps strengthen floc, preventing carryover into the
launders.
Question 7
Frequent clogging of the sludge discharge line is an indication that the sludge concentration is
_____. If this occurs, the operator should _____ the frequency of the sludge removal equipment.
pg. 2
,A. Optimal / maintain
B. Variable / stabilize
C. Too low / decrease
D. Too high / increase
Answer: D
Rationale: Frequent clogging indicates sludge concentration is too high, so the operator should
increase the frequency of sludge removal.
Question 8
When collecting TTHM samples, the sampling tap is left to run for a minimum of five minutes in
order to:
A. Stabilize the chemical composition
B. Allow the water to clear any sediment
C. Allow sufficient time for the temperature to become consistent
D. Ensure the sample is thoroughly mixed
Answer: A
Rationale: Flushing the tap for five minutes ensures the sample is representative by drawing
water from the distribution system rather than stagnant water in the service line.
Question 9
Chlorine dioxide reacts with water to form:
A. Cl⁻ ions and ClO₃⁻ ions
B. ClO₂⁻ ions and Cl⁻ ions
C. ClO⁻ ions and ClO₄⁻ ions
D. ClO₂⁻ ions and ClO₃⁻ ions
Answer: D
Rationale: Chlorine dioxide reacts with water to form chlorite (ClO₂⁻) and chlorate (ClO₃⁻) ions.
Question 10
Early turbidity breakthrough or rapid head loss buildup on a conventional filter plant operation
can often result from:
A. Excessive backwashing rates
B. Improper coagulation
C. Bad vacuum regulating valve diaphragm
D. Poor chemical treatment
Answer: B
pg. 3
, Rationale: Improper coagulation causes poor floc formation, leading to early turbidity
breakthrough and rapid head loss buildup.
Question 11
The proper list of diseases that may be transmitted by water:
A. Head loss, turbidity, and run time
B. Giardiasis, typhoid fever, dysentery, and Hepatitis A
C. Rising sludge blanket due to temperature change
D. Chlorine gas will lower the pH of the water
Answer: B
Rationale: Giardiasis, typhoid fever, dysentery, and Hepatitis A are all waterborne diseases
transmitted through contaminated water.
Question 12
The flocculation process is:
A. Mechanical
B. Thermal
C. Bacteriological
D. Chemical
Answer: A
Rationale: Flocculation is a mechanical process where gentle mixing brings particles together to
form larger floc.
Question 13
When used as a filter aid, polymer overdosing can result in:
A. An uneven flow and short circuiting
B. Accelerated head loss buildup
C. Allow wastewater discharges into the reservoir
D. Excessive coagulant has been fed
Answer: B
Rationale: Overdosing polymer causes accelerated head loss buildup as the filter media becomes
clogged with excess floc.
Question 14
In split treatment, a portion of the water, about 90%, is treated with an excess amount of lime to
remove magnesium at a pH of over:
pg. 4
Comprehensive Study Guide with Actual Exam Questions,
Verified Correct Answers and Detailed Rationales | Latest
Update -2026/2027
Question 1
Theoretically it takes ______ of chlorine to oxidize 1 mg/L of hydrogen sulfide to the sulfate
form.
A. 6.24 mg/L
B. 4.16 mg/L
C. 12.48 mg/L
D. 8.32 mg/L
Answer: D
Rationale: The theoretical chlorine demand for oxidizing hydrogen sulfide to sulfate is 8.32
mg/L of chlorine per 1 mg/L of H₂S.
Question 2
The polymer most frequently found to be effective in the collection and removal of particles
from water is a:
A. Low molecular weight, anionic polymer
B. Medium molecular weight, non-ionic polymer
C. High molecular weight, amphoteric polymer
D. High molecular weight, cationic polymer
Answer: D
Rationale: High molecular weight cationic polymers are most effective as coagulant aids
because they neutralize the negative charge of particles and promote floc formation.
Question 3
Recarbonation is necessary after lime softening in order to:
A. Reduce the scale forming tendencies of supersaturated water
B. Increase the pH to enhance disinfection
C. Reduce the turbidity of the water
D. Stabilize the chlorine levels in the water
Answer: A
pg. 1
,Rationale: Recarbonation adds carbon dioxide to reduce the pH and stabilize the water,
preventing calcium carbonate scale formation in the distribution system.
Question 4
Mud ball evaluation indicates a sample to be 2.5% to 5%. This is considered to be:
A. Good
B. Normal
C. Great
D. Bad
Answer: B
Rationale: A mud ball content of 2.5% to 5% is considered normal. Higher percentages indicate
poor backwashing and media problems.
Question 5
The metabolic process that consumes oxygen and releases carbon dioxide is:
A. Transpiration
B. Photosynthesis
C. Oxidation
D. Respiration
Answer: D
Rationale: Respiration is the metabolic process where organisms consume oxygen and release
carbon dioxide. Photosynthesis does the opposite.
Question 6
To stop slum floc from carrying over into the launders:
A. Remove turbidity
B. Detention is not critical in the flocculation process
C. Add or start polymer
D. Floc to prematurely settle out
Answer: C
Rationale: Adding or starting polymer helps strengthen floc, preventing carryover into the
launders.
Question 7
Frequent clogging of the sludge discharge line is an indication that the sludge concentration is
_____. If this occurs, the operator should _____ the frequency of the sludge removal equipment.
pg. 2
,A. Optimal / maintain
B. Variable / stabilize
C. Too low / decrease
D. Too high / increase
Answer: D
Rationale: Frequent clogging indicates sludge concentration is too high, so the operator should
increase the frequency of sludge removal.
Question 8
When collecting TTHM samples, the sampling tap is left to run for a minimum of five minutes in
order to:
A. Stabilize the chemical composition
B. Allow the water to clear any sediment
C. Allow sufficient time for the temperature to become consistent
D. Ensure the sample is thoroughly mixed
Answer: A
Rationale: Flushing the tap for five minutes ensures the sample is representative by drawing
water from the distribution system rather than stagnant water in the service line.
Question 9
Chlorine dioxide reacts with water to form:
A. Cl⁻ ions and ClO₃⁻ ions
B. ClO₂⁻ ions and Cl⁻ ions
C. ClO⁻ ions and ClO₄⁻ ions
D. ClO₂⁻ ions and ClO₃⁻ ions
Answer: D
Rationale: Chlorine dioxide reacts with water to form chlorite (ClO₂⁻) and chlorate (ClO₃⁻) ions.
Question 10
Early turbidity breakthrough or rapid head loss buildup on a conventional filter plant operation
can often result from:
A. Excessive backwashing rates
B. Improper coagulation
C. Bad vacuum regulating valve diaphragm
D. Poor chemical treatment
Answer: B
pg. 3
, Rationale: Improper coagulation causes poor floc formation, leading to early turbidity
breakthrough and rapid head loss buildup.
Question 11
The proper list of diseases that may be transmitted by water:
A. Head loss, turbidity, and run time
B. Giardiasis, typhoid fever, dysentery, and Hepatitis A
C. Rising sludge blanket due to temperature change
D. Chlorine gas will lower the pH of the water
Answer: B
Rationale: Giardiasis, typhoid fever, dysentery, and Hepatitis A are all waterborne diseases
transmitted through contaminated water.
Question 12
The flocculation process is:
A. Mechanical
B. Thermal
C. Bacteriological
D. Chemical
Answer: A
Rationale: Flocculation is a mechanical process where gentle mixing brings particles together to
form larger floc.
Question 13
When used as a filter aid, polymer overdosing can result in:
A. An uneven flow and short circuiting
B. Accelerated head loss buildup
C. Allow wastewater discharges into the reservoir
D. Excessive coagulant has been fed
Answer: B
Rationale: Overdosing polymer causes accelerated head loss buildup as the filter media becomes
clogged with excess floc.
Question 14
In split treatment, a portion of the water, about 90%, is treated with an excess amount of lime to
remove magnesium at a pH of over:
pg. 4
