Oregon Drinking Water Operator Exam – Full
Mock Exam Newest (2025 - 2026 Update) From
Real Past Papers Questions – A Set Of 100
Most Common Exam Frequently Tested
Questions And Answers In Details 100%
Verified Exam Highly Recommendable For
Grade A+
1. What is the primary purpose of drinking water treatment?
A. Increase water temperature
B. Add minerals
C. Answer: Remove contaminants and produce safe drinking water
D. Increase water pressure
Explanation: The main goal of drinking water treatment is to remove physical,
chemical, and biological contaminants to protect public health.
2. Which process removes large debris such as sticks and leaves?
A. Disinfection
B. Fluoridation
C. Answer: Screening
D. Softening
Explanation: Screening is the first treatment step that removes large floating
materials before additional treatment.
, 3. Which microorganism is commonly used as an indicator of fecal
contamination?
A. Giardia
B. Virus
C. Algae
D. Answer: Escherichia coli (E. coli)
Explanation: E. coli indicates possible fecal contamination and the potential
presence of disease-causing organisms.
4. Which treatment chemical is most commonly used for disinfection?
A. Lime
B. Alum
C. Answer: Chlorine
D. Soda ash
Explanation: Chlorine is widely used because it effectively kills harmful
microorganisms and provides a disinfectant residual.
5. What is turbidity?
A. Water hardness
B. Water temperature
C. Answer: Cloudiness caused by suspended particles
D. Water pressure
Explanation: Turbidity measures suspended materials that reduce water clarity
and may interfere with disinfection.
6. What instrument measures chlorine residual?
A. pH meter
, B. Flow meter
C. Thermometer
D. Answer: Colorimeter
Explanation: A colorimeter measures chlorine concentration using color
comparison methods.
7. What is the ideal purpose of coagulation?
A. Destroy bacteria
B. Lower temperature
C. Answer: Destabilize suspended particles
D. Remove dissolved oxygen
Explanation: Coagulation allows tiny particles to combine into larger flocs for
removal.
8. Which process follows coagulation?
A. Disinfection
B. Fluoridation
C. Answer: Flocculation
D. Aeration
Explanation: Gentle mixing during flocculation encourages particles to form larger,
settleable flocs.
9. What occurs during sedimentation?
A. Chlorine is added
B. Oxygen is removed
C. Answer: Heavy particles settle by gravity
D. Water is softened
Mock Exam Newest (2025 - 2026 Update) From
Real Past Papers Questions – A Set Of 100
Most Common Exam Frequently Tested
Questions And Answers In Details 100%
Verified Exam Highly Recommendable For
Grade A+
1. What is the primary purpose of drinking water treatment?
A. Increase water temperature
B. Add minerals
C. Answer: Remove contaminants and produce safe drinking water
D. Increase water pressure
Explanation: The main goal of drinking water treatment is to remove physical,
chemical, and biological contaminants to protect public health.
2. Which process removes large debris such as sticks and leaves?
A. Disinfection
B. Fluoridation
C. Answer: Screening
D. Softening
Explanation: Screening is the first treatment step that removes large floating
materials before additional treatment.
, 3. Which microorganism is commonly used as an indicator of fecal
contamination?
A. Giardia
B. Virus
C. Algae
D. Answer: Escherichia coli (E. coli)
Explanation: E. coli indicates possible fecal contamination and the potential
presence of disease-causing organisms.
4. Which treatment chemical is most commonly used for disinfection?
A. Lime
B. Alum
C. Answer: Chlorine
D. Soda ash
Explanation: Chlorine is widely used because it effectively kills harmful
microorganisms and provides a disinfectant residual.
5. What is turbidity?
A. Water hardness
B. Water temperature
C. Answer: Cloudiness caused by suspended particles
D. Water pressure
Explanation: Turbidity measures suspended materials that reduce water clarity
and may interfere with disinfection.
6. What instrument measures chlorine residual?
A. pH meter
, B. Flow meter
C. Thermometer
D. Answer: Colorimeter
Explanation: A colorimeter measures chlorine concentration using color
comparison methods.
7. What is the ideal purpose of coagulation?
A. Destroy bacteria
B. Lower temperature
C. Answer: Destabilize suspended particles
D. Remove dissolved oxygen
Explanation: Coagulation allows tiny particles to combine into larger flocs for
removal.
8. Which process follows coagulation?
A. Disinfection
B. Fluoridation
C. Answer: Flocculation
D. Aeration
Explanation: Gentle mixing during flocculation encourages particles to form larger,
settleable flocs.
9. What occurs during sedimentation?
A. Chlorine is added
B. Oxygen is removed
C. Answer: Heavy particles settle by gravity
D. Water is softened
