North Carolina Water Treatment
Operator Examination — Class I
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of water treatment?
A. To add minerals for taste
B. To remove harmful contaminants and pathogens
C. To change water color
D. To increase water hardness
Rationale: The main goal of water treatment is to make water safe
for human consumption by removing harmful contaminants and
pathogens.
2. Which of the following is a common physical method of water
treatment?
, A. Coagulation
B. Chlorination
C. Sedimentation
D. Ozonation
Rationale: Sedimentation is a physical process where solids settle out
of water due to gravity.
3. Coagulation is primarily used to:
A. Kill bacteria
B. Aggregate suspended particles for easier removal
C. Adjust pH
D. Add fluoride
Rationale: Coagulation helps small particles clump together to form
larger particles that can be removed by sedimentation or filtration.
4. What is the most common coagulant used in water treatment?
A. Sodium bicarbonate
B. Aluminum sulfate (alum)
C. Chlorine
D. Sodium hypochlorite
Rationale: Aluminum sulfate, or alum, is widely used to coagulate
fine particles in water treatment.
5. Which water quality parameter indicates the presence of organic
matter that can react with chlorine?
A. Turbidity
, B. Total Organic Carbon (TOC)
C. pH
D. Hardness
Rationale: TOC measures organic matter that can react with chlorine
to form disinfection by-products.
6. The pH of water affects:
A. Taste only
B. Coagulation, corrosion, and disinfection efficiency
C. Only hardness
D. Color
Rationale: pH influences chemical reactions during coagulation, can
affect corrosion, and impacts disinfection effectiveness.
7. What is the purpose of rapid mixing in water treatment?
A. Remove chlorine
B. Distribute coagulants evenly throughout the water
C. Slow sedimentation
D. Adjust pH
Rationale: Rapid mixing ensures that coagulants are evenly dispersed
to maximize particle aggregation.
8. Which unit process removes settled solids after coagulation?
A. Filtration
B. Chlorination
C. Sedimentation
, D. Aeration
Rationale: Sedimentation allows coagulated particles to settle out of
the water.
9. What is the main function of a filter in water treatment?
A. Adjust pH
B. Remove remaining suspended particles after sedimentation
C. Disinfect water
D. Add minerals
Rationale: Filtration removes particles that were not removed during
sedimentation.
10. Slow sand filters primarily rely on which mechanism?
A. Chemical precipitation
B. Biological activity in the schmutzdecke
C. Chlorination
D. Coagulation
Rationale: Slow sand filters rely on a biologically active layer
(schmutzdecke) to remove pathogens and particles.
11. What type of filter is commonly used in Class I water treatment
plants?
A. Rapid sand filter
B. Multi-media filter
C. Reverse osmosis
D. Ultraviolet filter
Operator Examination — Class I
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of water treatment?
A. To add minerals for taste
B. To remove harmful contaminants and pathogens
C. To change water color
D. To increase water hardness
Rationale: The main goal of water treatment is to make water safe
for human consumption by removing harmful contaminants and
pathogens.
2. Which of the following is a common physical method of water
treatment?
, A. Coagulation
B. Chlorination
C. Sedimentation
D. Ozonation
Rationale: Sedimentation is a physical process where solids settle out
of water due to gravity.
3. Coagulation is primarily used to:
A. Kill bacteria
B. Aggregate suspended particles for easier removal
C. Adjust pH
D. Add fluoride
Rationale: Coagulation helps small particles clump together to form
larger particles that can be removed by sedimentation or filtration.
4. What is the most common coagulant used in water treatment?
A. Sodium bicarbonate
B. Aluminum sulfate (alum)
C. Chlorine
D. Sodium hypochlorite
Rationale: Aluminum sulfate, or alum, is widely used to coagulate
fine particles in water treatment.
5. Which water quality parameter indicates the presence of organic
matter that can react with chlorine?
A. Turbidity
, B. Total Organic Carbon (TOC)
C. pH
D. Hardness
Rationale: TOC measures organic matter that can react with chlorine
to form disinfection by-products.
6. The pH of water affects:
A. Taste only
B. Coagulation, corrosion, and disinfection efficiency
C. Only hardness
D. Color
Rationale: pH influences chemical reactions during coagulation, can
affect corrosion, and impacts disinfection effectiveness.
7. What is the purpose of rapid mixing in water treatment?
A. Remove chlorine
B. Distribute coagulants evenly throughout the water
C. Slow sedimentation
D. Adjust pH
Rationale: Rapid mixing ensures that coagulants are evenly dispersed
to maximize particle aggregation.
8. Which unit process removes settled solids after coagulation?
A. Filtration
B. Chlorination
C. Sedimentation
, D. Aeration
Rationale: Sedimentation allows coagulated particles to settle out of
the water.
9. What is the main function of a filter in water treatment?
A. Adjust pH
B. Remove remaining suspended particles after sedimentation
C. Disinfect water
D. Add minerals
Rationale: Filtration removes particles that were not removed during
sedimentation.
10. Slow sand filters primarily rely on which mechanism?
A. Chemical precipitation
B. Biological activity in the schmutzdecke
C. Chlorination
D. Coagulation
Rationale: Slow sand filters rely on a biologically active layer
(schmutzdecke) to remove pathogens and particles.
11. What type of filter is commonly used in Class I water treatment
plants?
A. Rapid sand filter
B. Multi-media filter
C. Reverse osmosis
D. Ultraviolet filter
