Drinking Water Treatment Practice Exam –
EXAM STUDY GUIDE 2026/2027
ACCURATE QUESTIONS WITH CORRECT
DETAILED SOLUTIONS || 100%
GUARANTEED PASS NEWEST VERSION
Description: This comprehensive practice exam contains 200 multiple-choice
questions designed for candidates preparing for the Ohio Class 1 Drinking Water
Treatment Operator Certification Exam. The content aligns with the Ohio EPA Class I
Need-to-Know Criteria and the ABC/WPI standardized exam outline, covering
Treatment Process, Laboratory Analysis, Equipment Operation & Maintenance, Source
Water Characteristics, and Security/Safety/Administrative Procedures.
Keywords: Ohio Class 1, Drinking Water Treatment, Water Operator Certification, ABC
Exam, WPI Exam, Need-to-Know Criteria, Treatment Process, Coagulation, Flocculation,
Sedimentation, Filtration, Disinfection, Chlorination, Laboratory Analysis, Equipment
Maintenance, Source Water, Safety, Practice Exam, 2026, 2027.
SECTION 1: TREATMENT PROCESS (Questions 1–70)
1. What is the primary purpose of coagulation in drinking water treatment?
A. To kill pathogenic microorganisms
B. To destabilize suspended particles so they can form removable flocs ✅
,C. To remove dissolved gases from water
D. To adjust the pH of the water
2. Which chemical is the most commonly used primary coagulant in water
treatment?
A. Lime
B. Aluminum sulfate (alum) ✅
C. Sodium hydroxide
D. Potassium permanganate
3. Flocculation differs from coagulation in that flocculation involves:
A. Rapid mixing to disperse chemicals
B. Gentle agitation to encourage particles to clump together ✅
C. Chemical oxidation of contaminants
D. Gravity settling of particles
4. What is the typical detention time for a flocculation basin?
A. 1 to 5 seconds
B. 15 to 45 minutes ✅
C. 2 to 4 hours
D. 12 to 24 hours
5. In a conventional surface water treatment plant, the sudden increase in raw
water turbidity from 5 NTU to 50 NTU requires which immediate operational
adjustment?
A. Decrease coagulant dosage
B. Increase coagulant dosage proportionally ✅
C. Increase filter backwash frequency only
D. Reduce the filtration rate immediately
,6. Sedimentation removes particles primarily by:
A. Chemical oxidation
B. Gravity settling ✅
C. Air stripping
D. Filtration through sand
7. What device collects settled water as it leaves the sedimentation basin?
A. Effluent launder ✅
B. Weir plate
C. Baffle wall
D. Sludge scraper
8. Frequent clogging of the sludge discharge line from a sedimentation basin
indicates that the sludge concentration is:
A. Too low; decrease removal frequency
B. Too high; increase removal frequency ✅
C. Optimal; maintain current operations
D. Variable; stabilize chemical feed
9. The primary purpose of a rapid sand filter is to:
A. Remove dissolved salts
B. Remove fine particles that remain after sedimentation ✅
C. Kill bacteria through oxidation
D. Soften hard water
10. The common operating rate for a rapid sand filter is:
A. 0.5 to 1.0 gpm/ft²
B. 2 to 6 gpm/ft² ✅
, C. 8 to 12 gpm/ft²
D. 15 to 20 gpm/ft²
11. A filter effluent turbidity spike immediately after backwashing is most
commonly caused by:
A. Excessive sedimentation detention time
B. Filter ripening before the media develops effective particle removal capability ✅
C. Low raw water alkalinity
D. Excessive chlorine contact time
12. Excessive head loss across a filter is most likely caused by:
A. Low chlorine demand
B. Accumulation of trapped solids within the filter media ✅
C. Insufficient sedimentation basin volume
D. Excessive alkalinity
13. Backwashing a filter involves:
A. Reversing flow through the filter media to remove entrapped solids ✅
B. Adding chemicals to disinfect the filter media
C. Increasing forward flow to flush the filter
D. Adding sand to the filter surface
14. The best indicator that a filter should be backwashed is:
A. Filter effluent turbidity ✅
B. Raw water temperature
C. Chlorine residual
D. Sedimentation basin sludge level
15. When backwashing a filter, the backwash valve should be opened slowly to
prevent:
EXAM STUDY GUIDE 2026/2027
ACCURATE QUESTIONS WITH CORRECT
DETAILED SOLUTIONS || 100%
GUARANTEED PASS NEWEST VERSION
Description: This comprehensive practice exam contains 200 multiple-choice
questions designed for candidates preparing for the Ohio Class 1 Drinking Water
Treatment Operator Certification Exam. The content aligns with the Ohio EPA Class I
Need-to-Know Criteria and the ABC/WPI standardized exam outline, covering
Treatment Process, Laboratory Analysis, Equipment Operation & Maintenance, Source
Water Characteristics, and Security/Safety/Administrative Procedures.
Keywords: Ohio Class 1, Drinking Water Treatment, Water Operator Certification, ABC
Exam, WPI Exam, Need-to-Know Criteria, Treatment Process, Coagulation, Flocculation,
Sedimentation, Filtration, Disinfection, Chlorination, Laboratory Analysis, Equipment
Maintenance, Source Water, Safety, Practice Exam, 2026, 2027.
SECTION 1: TREATMENT PROCESS (Questions 1–70)
1. What is the primary purpose of coagulation in drinking water treatment?
A. To kill pathogenic microorganisms
B. To destabilize suspended particles so they can form removable flocs ✅
,C. To remove dissolved gases from water
D. To adjust the pH of the water
2. Which chemical is the most commonly used primary coagulant in water
treatment?
A. Lime
B. Aluminum sulfate (alum) ✅
C. Sodium hydroxide
D. Potassium permanganate
3. Flocculation differs from coagulation in that flocculation involves:
A. Rapid mixing to disperse chemicals
B. Gentle agitation to encourage particles to clump together ✅
C. Chemical oxidation of contaminants
D. Gravity settling of particles
4. What is the typical detention time for a flocculation basin?
A. 1 to 5 seconds
B. 15 to 45 minutes ✅
C. 2 to 4 hours
D. 12 to 24 hours
5. In a conventional surface water treatment plant, the sudden increase in raw
water turbidity from 5 NTU to 50 NTU requires which immediate operational
adjustment?
A. Decrease coagulant dosage
B. Increase coagulant dosage proportionally ✅
C. Increase filter backwash frequency only
D. Reduce the filtration rate immediately
,6. Sedimentation removes particles primarily by:
A. Chemical oxidation
B. Gravity settling ✅
C. Air stripping
D. Filtration through sand
7. What device collects settled water as it leaves the sedimentation basin?
A. Effluent launder ✅
B. Weir plate
C. Baffle wall
D. Sludge scraper
8. Frequent clogging of the sludge discharge line from a sedimentation basin
indicates that the sludge concentration is:
A. Too low; decrease removal frequency
B. Too high; increase removal frequency ✅
C. Optimal; maintain current operations
D. Variable; stabilize chemical feed
9. The primary purpose of a rapid sand filter is to:
A. Remove dissolved salts
B. Remove fine particles that remain after sedimentation ✅
C. Kill bacteria through oxidation
D. Soften hard water
10. The common operating rate for a rapid sand filter is:
A. 0.5 to 1.0 gpm/ft²
B. 2 to 6 gpm/ft² ✅
, C. 8 to 12 gpm/ft²
D. 15 to 20 gpm/ft²
11. A filter effluent turbidity spike immediately after backwashing is most
commonly caused by:
A. Excessive sedimentation detention time
B. Filter ripening before the media develops effective particle removal capability ✅
C. Low raw water alkalinity
D. Excessive chlorine contact time
12. Excessive head loss across a filter is most likely caused by:
A. Low chlorine demand
B. Accumulation of trapped solids within the filter media ✅
C. Insufficient sedimentation basin volume
D. Excessive alkalinity
13. Backwashing a filter involves:
A. Reversing flow through the filter media to remove entrapped solids ✅
B. Adding chemicals to disinfect the filter media
C. Increasing forward flow to flush the filter
D. Adding sand to the filter surface
14. The best indicator that a filter should be backwashed is:
A. Filter effluent turbidity ✅
B. Raw water temperature
C. Chlorine residual
D. Sedimentation basin sludge level
15. When backwashing a filter, the backwash valve should be opened slowly to
prevent:
