NEW MEXICO WATER TREATMENT OPERATOR LEVEL I PRACTICE EXAM QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2026 Q&A |LATEST EXAM
UPDATE 2026/2027.
What is the primary purpose of pre-chlorination in a surface water treatment plant?
A. To increase water hardness
B. To control algae and taste/odor-causing organisms
C. To reduce the pH of the raw water
D. To provide secondary disinfection
🟢B
🔴 RATIONALE: Pre-chlorination is commonly used at the intake or rapid mix stage to oxidize iron
and manganese and to kill algae and other biological organisms that cause taste and odor
problems.
Which federal law governs the quality of drinking water provided by public water systems?
A. Clean Water Act
B. Safe Drinking Water Act
C. Resource Conservation and Recovery Act
D. National Environmental Policy Act
🟢B
🔴 RATIONALE: The Safe Drinking Water Act (SDWA) is the primary federal law that ensures the
quality of drinking water in the United States by setting standards for contaminants.
What does a high turbidity reading in treated water indicate?
A. Excessive fluoride levels
B. Ineffective filtration or flocculation
C. High dissolved oxygen levels
D. Proper disinfection contact time
,🟢B
🔴 RATIONALE: Turbidity is a measure of water cloudiness; high readings after filtration indicate
that particles are passing through the filters, meaning the flocculation or filtration processes are
failing.
Which chemical is most commonly used for coagulation in water treatment?
A. Sodium hydroxide
B. Ferric chloride
C. Calcium hypochlorite
D. Aluminum sulfate (alum)
🟢D
🔴 RATIONALE: Aluminum sulfate, commonly known as alum, is the most widely used coagulant
because it is effective, relatively inexpensive, and readily available.
What is the main safety risk when handling chlorine gas?
A. It is highly flammable
B. It is lighter than air and dissipates quickly
C. It is a toxic, heavier-than-air gas that can cause respiratory damage
D. It reacts violently with water to produce electricity
🟢C
🔴 RATIONALE: Chlorine gas is toxic and heavier than air, meaning it will settle in low-lying areas
during a leak, posing a severe inhalation hazard.
What is the purpose of the backwashing process in a rapid sand filter?
A. To sterilize the filter media
B. To remove accumulated solids from the filter bed
C. To increase the water flow rate
,D. To settle out heavy metals
🟢B
🔴 RATIONALE: Backwashing reverses the flow of water through the filter to expand the media
and flush out the trapped particles collected during the filtration cycle.
Which term describes the process of water soaking into the soil and moving downward?
A. Evaporation
B. Transpiration
C. Infiltration
D. Condensation
🟢C
🔴 RATIONALE: Infiltration is the physical process by which water on the ground surface enters
the soil.
Why must an operator maintain a residual disinfectant in the distribution system?
A. To prevent corrosion of pipes
B. To provide protection against microbial contamination
C. To clarify the water
D. To remove scale buildup
🟢B
🔴 RATIONALE: Maintaining a disinfectant residual ensures that any biological contamination
introduced into the distribution system can be neutralized.
What is the correct way to operate a fire extinguisher on a small electrical fire?
A. Aim at the flames
B. Aim at the base of the fire
C. Use water to cool the area
, D. Use a foam-based extinguisher only
🟢B
🔴 RATIONALE: When using a fire extinguisher, always aim at the base of the fire to smother the
fuel source rather than just aiming at the visible flames.
Which water quality parameter is measured using the DPD colorimetric method?
A. pH
B. Chlorine residual
C. Hardness
D. Alkalinity
🟢B
🔴 RATIONALE: The DPD (N,N-diethyl-p-phenylenediamine) test is the standard colorimetric
method for measuring free and total chlorine residuals in water.
If a pump loses its prime, what should the operator do first?
A. Increase the pump speed
B. Shut down the pump and investigate the intake
C. Add more chemicals to the suction line
D. Open the discharge valve fully
🟢B
🔴 RATIONALE: A pump that loses prime cannot move water effectively and may become
damaged; shutting it down prevents mechanical failure while the suction line is checked for air
leaks.
What is the relationship between water temperature and chlorine disinfection efficiency?
A. Higher temperatures improve disinfection
B. Lower temperatures improve disinfection
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2026 Q&A |LATEST EXAM
UPDATE 2026/2027.
What is the primary purpose of pre-chlorination in a surface water treatment plant?
A. To increase water hardness
B. To control algae and taste/odor-causing organisms
C. To reduce the pH of the raw water
D. To provide secondary disinfection
🟢B
🔴 RATIONALE: Pre-chlorination is commonly used at the intake or rapid mix stage to oxidize iron
and manganese and to kill algae and other biological organisms that cause taste and odor
problems.
Which federal law governs the quality of drinking water provided by public water systems?
A. Clean Water Act
B. Safe Drinking Water Act
C. Resource Conservation and Recovery Act
D. National Environmental Policy Act
🟢B
🔴 RATIONALE: The Safe Drinking Water Act (SDWA) is the primary federal law that ensures the
quality of drinking water in the United States by setting standards for contaminants.
What does a high turbidity reading in treated water indicate?
A. Excessive fluoride levels
B. Ineffective filtration or flocculation
C. High dissolved oxygen levels
D. Proper disinfection contact time
,🟢B
🔴 RATIONALE: Turbidity is a measure of water cloudiness; high readings after filtration indicate
that particles are passing through the filters, meaning the flocculation or filtration processes are
failing.
Which chemical is most commonly used for coagulation in water treatment?
A. Sodium hydroxide
B. Ferric chloride
C. Calcium hypochlorite
D. Aluminum sulfate (alum)
🟢D
🔴 RATIONALE: Aluminum sulfate, commonly known as alum, is the most widely used coagulant
because it is effective, relatively inexpensive, and readily available.
What is the main safety risk when handling chlorine gas?
A. It is highly flammable
B. It is lighter than air and dissipates quickly
C. It is a toxic, heavier-than-air gas that can cause respiratory damage
D. It reacts violently with water to produce electricity
🟢C
🔴 RATIONALE: Chlorine gas is toxic and heavier than air, meaning it will settle in low-lying areas
during a leak, posing a severe inhalation hazard.
What is the purpose of the backwashing process in a rapid sand filter?
A. To sterilize the filter media
B. To remove accumulated solids from the filter bed
C. To increase the water flow rate
,D. To settle out heavy metals
🟢B
🔴 RATIONALE: Backwashing reverses the flow of water through the filter to expand the media
and flush out the trapped particles collected during the filtration cycle.
Which term describes the process of water soaking into the soil and moving downward?
A. Evaporation
B. Transpiration
C. Infiltration
D. Condensation
🟢C
🔴 RATIONALE: Infiltration is the physical process by which water on the ground surface enters
the soil.
Why must an operator maintain a residual disinfectant in the distribution system?
A. To prevent corrosion of pipes
B. To provide protection against microbial contamination
C. To clarify the water
D. To remove scale buildup
🟢B
🔴 RATIONALE: Maintaining a disinfectant residual ensures that any biological contamination
introduced into the distribution system can be neutralized.
What is the correct way to operate a fire extinguisher on a small electrical fire?
A. Aim at the flames
B. Aim at the base of the fire
C. Use water to cool the area
, D. Use a foam-based extinguisher only
🟢B
🔴 RATIONALE: When using a fire extinguisher, always aim at the base of the fire to smother the
fuel source rather than just aiming at the visible flames.
Which water quality parameter is measured using the DPD colorimetric method?
A. pH
B. Chlorine residual
C. Hardness
D. Alkalinity
🟢B
🔴 RATIONALE: The DPD (N,N-diethyl-p-phenylenediamine) test is the standard colorimetric
method for measuring free and total chlorine residuals in water.
If a pump loses its prime, what should the operator do first?
A. Increase the pump speed
B. Shut down the pump and investigate the intake
C. Add more chemicals to the suction line
D. Open the discharge valve fully
🟢B
🔴 RATIONALE: A pump that loses prime cannot move water effectively and may become
damaged; shutting it down prevents mechanical failure while the suction line is checked for air
leaks.
What is the relationship between water temperature and chlorine disinfection efficiency?
A. Higher temperatures improve disinfection
B. Lower temperatures improve disinfection
