TEXAS WATER OPERATOR LICENSING LEVEL
IV EXAM QUESTIONS WITH CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A | INSTANT
DOWNLOAD PDF
1. What is the primary purpose of a Clearwell in a surface water
treatment plant?
A. Provide additional filtration
B. Store sludge before disposal
C. Provide chlorine contact time
D. Remove hardness
Answer: C
Provides required disinfection contact time before distribution.
2. Which disinfectant forms the least amount of trihalomethanes
(THMs)?
A. Chlorine gas
B. Chloramines
C. Chlorine dioxide
D. Hypochlorite
Answer: C
Chlorine dioxide produces significantly fewer THMs than free chlorine.
,3. The CT concept used in disinfection combines disinfectant
concentration with:
A. Flow rate
B. pH
C. Temperature
D. Contact time
Answer: D
CT = Concentration × Time; used to verify pathogen inactivation.
4. What is the maximum allowable turbidity for filtered water in
Texas (95% of samples)?
A. 0.1 NTU
B. 0.3 NTU
C. 0.5 NTU
D. 1.0 NTU
Answer: B
Regulations require 0.3 NTU or less for 95% of readings.
5. Free chlorine residual in the distribution system must be at least:
A. 0.1 mg/L
B. 0.2 mg/L
C. 0.5 mg/L
D. 1.0 mg/L
Answer: B
Texas requires 0.2 mg/L minimum free chlorine in the distribution
system.
,6. What is the main purpose of coagulation?
A. Remove dissolved minerals
B. Neutralize particle charges
C. Increase alkalinity
D. Reduce chlorine demand
Answer: B
Coagulants destabilize particles by neutralizing charge.
7. Alum works best in which pH range?
A. 3–4
B. 4–6
C. 5.5–7.5
D. 8–10
Answer: C
Alum optimally forms floc in moderately acidic to neutral pH.
8. The most common cause of filter breakthrough is:
A. Too much backwash
B. Filter media too deep
C. Improper coagulation/floc
D. High temperature
Answer: C
Poor coagulation leads to small particles passing through filters.
9. A rapid rate filter typically operates at:
A. 1 gpm/ft²
B. 2–4 gpm/ft²
, C. 5–8 gpm/ft²
D. 10–12 gpm/ft²
Answer: B
Rapid sand filters commonly run at 2–4 gpm per square foot.
10. Breakpoint chlorination is achieved when:
A. Chlorine residual reaches 10 mg/L
B. Chloramines are fully formed
C. Ammonia demand is satisfied
D. Chlorine demand becomes zero
Answer: C
Breakpoint occurs after ammonia-consuming reactions complete.
11. Excessive head loss in a filter indicates:
A. Media is too coarse
B. Filter needs backwashing
C. Too much chlorine
D. Coagulant overdose
Answer: B
High head loss signals clogging and need for backwash.
12. The most critical parameter affecting chlorination efficiency is:
A. Hardness
B. Alkalinity
C. pH
D. Turbidity
IV EXAM QUESTIONS WITH CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A | INSTANT
DOWNLOAD PDF
1. What is the primary purpose of a Clearwell in a surface water
treatment plant?
A. Provide additional filtration
B. Store sludge before disposal
C. Provide chlorine contact time
D. Remove hardness
Answer: C
Provides required disinfection contact time before distribution.
2. Which disinfectant forms the least amount of trihalomethanes
(THMs)?
A. Chlorine gas
B. Chloramines
C. Chlorine dioxide
D. Hypochlorite
Answer: C
Chlorine dioxide produces significantly fewer THMs than free chlorine.
,3. The CT concept used in disinfection combines disinfectant
concentration with:
A. Flow rate
B. pH
C. Temperature
D. Contact time
Answer: D
CT = Concentration × Time; used to verify pathogen inactivation.
4. What is the maximum allowable turbidity for filtered water in
Texas (95% of samples)?
A. 0.1 NTU
B. 0.3 NTU
C. 0.5 NTU
D. 1.0 NTU
Answer: B
Regulations require 0.3 NTU or less for 95% of readings.
5. Free chlorine residual in the distribution system must be at least:
A. 0.1 mg/L
B. 0.2 mg/L
C. 0.5 mg/L
D. 1.0 mg/L
Answer: B
Texas requires 0.2 mg/L minimum free chlorine in the distribution
system.
,6. What is the main purpose of coagulation?
A. Remove dissolved minerals
B. Neutralize particle charges
C. Increase alkalinity
D. Reduce chlorine demand
Answer: B
Coagulants destabilize particles by neutralizing charge.
7. Alum works best in which pH range?
A. 3–4
B. 4–6
C. 5.5–7.5
D. 8–10
Answer: C
Alum optimally forms floc in moderately acidic to neutral pH.
8. The most common cause of filter breakthrough is:
A. Too much backwash
B. Filter media too deep
C. Improper coagulation/floc
D. High temperature
Answer: C
Poor coagulation leads to small particles passing through filters.
9. A rapid rate filter typically operates at:
A. 1 gpm/ft²
B. 2–4 gpm/ft²
, C. 5–8 gpm/ft²
D. 10–12 gpm/ft²
Answer: B
Rapid sand filters commonly run at 2–4 gpm per square foot.
10. Breakpoint chlorination is achieved when:
A. Chlorine residual reaches 10 mg/L
B. Chloramines are fully formed
C. Ammonia demand is satisfied
D. Chlorine demand becomes zero
Answer: C
Breakpoint occurs after ammonia-consuming reactions complete.
11. Excessive head loss in a filter indicates:
A. Media is too coarse
B. Filter needs backwashing
C. Too much chlorine
D. Coagulant overdose
Answer: B
High head loss signals clogging and need for backwash.
12. The most critical parameter affecting chlorination efficiency is:
A. Hardness
B. Alkalinity
C. pH
D. Turbidity
