AWWA PRACTICE TEST STUDY GUIDE
Actual 2025/2026 Questions and Verified Answers
Certified Water Industry Examination Preparation
SECTION 1: WATER TREATMENT PROCESSES
Q1: A water treatment plant is experiencing high turbidity in the settled water following the
flocculation basin. The operator notices that the floc particles are small and not settling
properly. Which of the following adjustments would MOST likely improve settling?
A. Increase the flash mix speed to create smaller, denser floc
B. Decrease the coagulant dosage to reduce chemical costs
C. Adjust the pH to optimize the coagulation process [CORRECT]
D. Bypass some flow around the flocculation basin
Correct Answer: C
Rationale: pH plays a critical role in coagulation efficiency. Most coagulants (like alum) have an
optimal pH range (typically 5.5-7.5) for forming large, settleable floc. Option A is incorrect
because increasing flash mix speed would actually shear floc particles. Option B is incorrect
because decreasing coagulant would likely worsen the problem. Option D is incorrect because
bypassing treatment would violate regulations and worsen effluent quality.
Q2: A water treatment operator conducts a jar test and determines that the optimal coagulant
dose is 15 mg/L. The plant flow rate is 4 MGD. How many pounds of coagulant will be needed
per day?
A. 250 lbs/day
B. 375 lbs/day
C. 500 lbs/day [CORRECT]
D. 625 lbs/day
Correct Answer: C
Rationale: Use the formula: lbs/day = Dose (mg/L) × Flow (MGD) × 8.34. Calculation: 15 mg/L ×
4 MGD × 8.34 = 500.4 lbs/day. Option A (250) results from forgetting to multiply by 8.34. Option
B (375) comes from using 6.24 (dry pounds formula) instead of 8.34. Option D (625) comes from
using 10.34 instead of 8.34.
, Q3: During the flocculation process, what is the primary purpose of tapered flocculation?
A. To maintain uniform mixing throughout all basins
B. To gradually reduce mixing energy as floc particles grow [CORRECT]
C. To increase mixing energy to break up large floc
D. To alternate between high and low mixing speeds
Correct Answer: B
Rationale: Tapered flocculation progressively reduces velocity gradients (G values) as floc travels
through basins, allowing floc particles to grow without being sheared apart. Option A describes
uniform mixing, not tapered. Option C would destroy floc. Option D describes intermittent
mixing, which is not standard practice.
Q4: A filter run is terminated when the effluent turbidity reaches 0.3 NTU. After backwashing,
the filter returns to service but immediately produces water at 0.4 NTU. What is the MOST likely
cause?
A. Mudball formation in the filter media
B. Air binding in the filter underdrains
C. Inadequate filter-to-waste duration [CORRECT]
D. Excessive backwash rate
Correct Answer: C
Rationale: After backwashing, filters require a filter-to-waste period to remove residual
backwash water and allow the media to settle and form an effective filtering mat. Option A
(mudballs) causes poor distribution but not necessarily immediate turbidity spikes. Option B (air
binding) causes cracking and poor filtration but usually develops over time. Option D (excessive
backwash rate) could disrupt media stratification but wouldn't necessarily cause immediate high
turbidity.
Q5: What is the minimum chlorine contact time (CT) value required for Giardia inactivation at
10°C and pH 7.5 using free chlorine?
A. 25 mg/L·min
B. 50 mg/L·min
C. 75 mg/L·min
D. 100 mg/L·min [CORRECT]
Actual 2025/2026 Questions and Verified Answers
Certified Water Industry Examination Preparation
SECTION 1: WATER TREATMENT PROCESSES
Q1: A water treatment plant is experiencing high turbidity in the settled water following the
flocculation basin. The operator notices that the floc particles are small and not settling
properly. Which of the following adjustments would MOST likely improve settling?
A. Increase the flash mix speed to create smaller, denser floc
B. Decrease the coagulant dosage to reduce chemical costs
C. Adjust the pH to optimize the coagulation process [CORRECT]
D. Bypass some flow around the flocculation basin
Correct Answer: C
Rationale: pH plays a critical role in coagulation efficiency. Most coagulants (like alum) have an
optimal pH range (typically 5.5-7.5) for forming large, settleable floc. Option A is incorrect
because increasing flash mix speed would actually shear floc particles. Option B is incorrect
because decreasing coagulant would likely worsen the problem. Option D is incorrect because
bypassing treatment would violate regulations and worsen effluent quality.
Q2: A water treatment operator conducts a jar test and determines that the optimal coagulant
dose is 15 mg/L. The plant flow rate is 4 MGD. How many pounds of coagulant will be needed
per day?
A. 250 lbs/day
B. 375 lbs/day
C. 500 lbs/day [CORRECT]
D. 625 lbs/day
Correct Answer: C
Rationale: Use the formula: lbs/day = Dose (mg/L) × Flow (MGD) × 8.34. Calculation: 15 mg/L ×
4 MGD × 8.34 = 500.4 lbs/day. Option A (250) results from forgetting to multiply by 8.34. Option
B (375) comes from using 6.24 (dry pounds formula) instead of 8.34. Option D (625) comes from
using 10.34 instead of 8.34.
, Q3: During the flocculation process, what is the primary purpose of tapered flocculation?
A. To maintain uniform mixing throughout all basins
B. To gradually reduce mixing energy as floc particles grow [CORRECT]
C. To increase mixing energy to break up large floc
D. To alternate between high and low mixing speeds
Correct Answer: B
Rationale: Tapered flocculation progressively reduces velocity gradients (G values) as floc travels
through basins, allowing floc particles to grow without being sheared apart. Option A describes
uniform mixing, not tapered. Option C would destroy floc. Option D describes intermittent
mixing, which is not standard practice.
Q4: A filter run is terminated when the effluent turbidity reaches 0.3 NTU. After backwashing,
the filter returns to service but immediately produces water at 0.4 NTU. What is the MOST likely
cause?
A. Mudball formation in the filter media
B. Air binding in the filter underdrains
C. Inadequate filter-to-waste duration [CORRECT]
D. Excessive backwash rate
Correct Answer: C
Rationale: After backwashing, filters require a filter-to-waste period to remove residual
backwash water and allow the media to settle and form an effective filtering mat. Option A
(mudballs) causes poor distribution but not necessarily immediate turbidity spikes. Option B (air
binding) causes cracking and poor filtration but usually develops over time. Option D (excessive
backwash rate) could disrupt media stratification but wouldn't necessarily cause immediate high
turbidity.
Q5: What is the minimum chlorine contact time (CT) value required for Giardia inactivation at
10°C and pH 7.5 using free chlorine?
A. 25 mg/L·min
B. 50 mg/L·min
C. 75 mg/L·min
D. 100 mg/L·min [CORRECT]
