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Water Treatment Operator Licensing
Exam (suitable for Class C/B/A levels depending on
your state’s requirements).
The questions cover: water chemistry, treatment processes, disinfection, safety, math, and regulatory compliance.
- What is the primary purpose of coagulation in water treatment? A. Reduce hardness B. Remove suspended solids C. Add chlorine D. Control pH Coagulation causes fine suspended particles to clump together into larger particles (floc), making them easier to remove during sedimentation and filtration.
- Which chemical is most commonly used as a coagulant in water treatment? A. Calcium carbonate B. Chlorine C. Aluminum sulfate (alum) D. Sodium hypochlorite Alum is the most common coagulant used to destabilize particles in the water for removal.
- The pH of water is a measure of: A. Hardness B. Hydrogen ion concentration C. Alkalinity D. Turbidity pH measures the concentration of hydrogen ions and indicates whether water is acidic or basic.
- What is the ideal pH range for effective coagulation using alum? A. 3.0–4. B. 6.5–9. C. 5.5–7. D. 8.5–10. Alum works most efficiently within the pH range of 5.5 to 7.5.
- Which of the following is most commonly used for primary disinfection? A. Carbon dioxide B. Chlorine C. Alum D. Lime Chlorine is the most widely used primary disinfectant due to its effectiveness and residual capability.
- Which type of chlorine has the highest available chlorine content? A. Sodium hypochlorite B. Calcium hypochlorite C. Liquid chlorine gas
10.What is breakpoint chlorination? A. Point at which all pathogens are killed B. Point where chlorine demand is satisfied and free chlorine remains C. When chlorine is no longer effective D. Overfeeding of chlorine Breakpoint chlorination occurs when sufficient chlorine is added to oxidize all ammonia and organic compounds, resulting in free chlorine residual. 11.Which component is used to raise the pH of water during treatment? A. Sulfuric acid B. Sodium bisulfite C. Lime D. Alum Lime (calcium hydroxide) is added to increase the pH and adjust alkalinity. 12.What is the term for the total time water spends in a tank? A. Flow rate B. Gradient C. Detention time D. Contact velocity Detention time is the theoretical time water remains in a tank and is crucial for disinfection and sedimentation. 13.Which law governs the regulation of drinking water in the U.S.? A. Clean Water Act B. Resource Conservation Act
C. Safe Drinking Water Act D. Toxic Substances Control Act The Safe Drinking Water Act sets drinking water quality standards and oversees public water systems. 14.Which device is used to measure flow in a pipe? A. Turbidity meter B. pH meter C. Flow meter D. Jar tester Flow meters measure the volume of water passing through a system, essential for dosing and monitoring. 15.What is the purpose of a filter-to-waste process in a filter plant? A. Improve taste B. Prevent poor quality water from entering the distribution system after backwash C. Remove chlorine D. Reduce TDS After backwashing, filters may release turbid water temporarily. The filter-to-waste cycle prevents this water from entering the system. 16.Which material is most commonly used in rapid sand filters? A. Clay B. Silica sand C. Gravel only D. Lime
20.What is the typical free chlorine residual maintained in a distribution system? A. 0.05 mg/L B. 0.1 mg/L C. 0.2 to 0.5 mg/L D. 1.5 to 2.0 mg/L A minimum of 0.2 mg/L is commonly required to maintain disinfection throughout the system. 21.What is the primary goal of sedimentation? A. Raise pH B. Kill bacteria C. Remove flocculated particles D. Add alkalinity Sedimentation allows heavier floc particles to settle before filtration. 22.Chlorine gas is: A. Non-toxic B. Heavier than air C. Lighter than air D. Odorless Chlorine gas is heavier than air and can accumulate in low-lying areas, posing a hazard. 23.What does SCADA stand for? A. Supervisory Control And Data Assessment
B. Supervisory Control And Data Acquisition C. System Control And Direct Access D. Sample Collection And Data Acquisition SCADA systems are used to monitor and control treatment plant operations remotely. 24.What is the purpose of baffles in a chlorine contact basin? A. Reduce algae B. Increase contact time and prevent short-circuiting C. Decrease pH D. Remove solids Baffles direct the flow of water to maximize disinfection contact time. 25.What is the effect of temperature on chlorine disinfection? A. No effect B. More effective in cold water C. Less effective in cold water D. Stops at high temperature Chlorine is more effective at higher temperatures; colder water slows disinfection rates. 26.A pressure reading of 43.3 psi equals how many feet of head? A. 50 B. 100 C. 120
30.Chlorine demand is defined as: A. Amount remaining after disinfection B. Chlorine used up by reactions with contaminants C. Total chlorine added D. Disinfection rate Chlorine demand is the amount of chlorine consumed before a measurable residual is reached. 31.What is the standard detention time for a conventional sedimentation basin? A. 15 minutes B. 30 minutes C. 2 hours D. 5 hours A typical sedimentation basin requires about 2 hours for effective settling of flocculated particles. 32.What is the main advantage of using ozone as a disinfectant? A. Low cost B. Leaves long-lasting residual C. No byproducts D. Very strong oxidizer Ozone is a powerful disinfectant that inactivates a wide range of pathogens quickly.
33.What is the recommended maximum turbidity level for filtered water as per the Surface Water Treatment Rule? A. 0.1 NTU B. 0.3 NTU C. 1.0 NTU D. 2.0 NTU The EPA requires filtered water turbidity to be below 0.3 NTU in 95% of monthly samples. 34.Which component prevents water hammer in a distribution system? A. Check valve B. Surge tank C. Backflow preventer D. Gate valve Surge tanks absorb pressure fluctuations and prevent water hammer, which can damage pipes. 35.What is the main cause of taste and odor problems in surface water? A. Excess chlorine B. Algae and decaying organic matter C. High hardness D. Low turbidity Algal blooms and decaying vegetation release compounds that cause musty or earthy odors. 36.Which of the following is a secondary standard in drinking water? A. Arsenic
Hydrogen sulfide forms under anaerobic conditions and causes a rotten egg odor. 40.The typical filter backwash rate is: A. 0.5 gpm/ft² B. 15 gpm/ft² C. 50 gpm/ft² D. 100 gpm/ft² Rapid sand filters are backwashed at approximately 15 gallons per minute per square foot to remove trapped particles. 41.The term "free chlorine" refers to: A. Total chlorine available B. Combined chlorine C. Chlorine available for disinfection D. Chlorine gas in the air Free chlorine is the uncombined, active portion available to disinfect water. 42.A water main break may require what type of public notification? A. Consumer Confidence Report B. Boil Water Advisory C. EPA Violation Report D. Monthly Compliance Summary A boil water advisory is issued to protect public health when contamination is possible.
43.What is the best method to calibrate a turbidimeter? A. With distilled water B. With tap water C. Using standard NTU calibration solution D. With chlorine solution Calibration should be done with manufacturer-supplied or standard calibration solutions of known NTU values. 44.What is the maximum allowable level of nitrate in drinking water? A. 1 mg/L B. 5 mg/L C. 10 mg/L D. 50 mg/L The EPA Maximum Contaminant Level (MCL) for nitrate is 10 mg/L as nitrogen. 45.What instrument is used to measure water pressure? A. Thermometer B. Turbidimeter C. Pressure gauge D. Flow meter Pressure gauges measure system pressure and are essential for system monitoring and safety. 46.Which term describes the ability of water to resist pH change? A. pH level B. Turbidity
50.What does the term “lagooning” refer to in water treatment? A. Chlorine storage B. Filtration C. Settling solids in open ponds D. Iron removal Lagooning is a process where water is held in large open basins for sedimentation and treatment. 51.What is the best way to prevent nitrification in chloraminated systems? A. Increase pH B. Maintain proper chlorine-to-ammonia ratio C. Lower turbidity D. Use ozone Maintaining the proper Cl₂:NH₃ ratio prevents nitrifying bacteria from converting ammonia to nitrite/nitrate. 52.Which is a method of softening water? A. Aeration B. Ion exchange C. Chlorination D. Coagulation Ion exchange replaces calcium and magnesium ions with sodium, softening the water. 53.Which chemical is used to dechlorinate water? A. Sodium fluoride B. Sodium bisulfite
C. Alum D. Sodium hydroxide Sodium bisulfite is commonly used to neutralize chlorine before discharging water. 54.What is the purpose of a sanitary seal on a well? A. Prevents chlorine loss B. Prevents surface contamination C. Holds pipe pressure D. Prevents air release Sanitary seals prevent contaminants from entering the well casing. 55.What is the best method to monitor chlorine residual in the field? A. UV spectrometer B. Jar test C. DPD colorimetric method D. TDS meter The DPD method is the standard field test for chlorine residual. 56.The acronym MCL stands for: A. Maximum Chlorine Level B. Minimum Control Level C. Maximum Contaminant Level D. Monitoring Control Level MCL refers to the highest level of a contaminant allowed in drinking water.
C. Reduced turbidity D. Less sludge Overdosing coagulants can create charge reversal, leading to poor floc formation and more sludge. 61.Which process is primarily responsible for removing dissolved iron and manganese? A. Coagulation B. Sedimentation C. Oxidation followed by filtration D. Softening Iron and manganese are typically oxidized (e.g., with chlorine or permanganate) and then filtered out. 62.The term "backflow" refers to: A. Water returning to the reservoir B. Reverse flow of water that can contaminate the supply C. Overpressure in pipes D. Cross-connection of electrical systems Backflow can draw contaminants into clean water supplies if not properly controlled. 63.What is a cross-connection? A. Two filter beds connected B. A physical link between potable and non-potable water sources C. A pipe connected to a drain
D. A connection between reservoirs Cross-connections can lead to backflow contamination if not prevented. 64.What device is commonly used to prevent backflow in a water system? A. Gate valve B. PRV (Pressure Reducing Valve) C. Double check valve assembly D. Butterfly valve Double check valve assemblies are used to prevent backflow and protect potable systems. 65.The best time to collect a chlorine residual sample is: A. After disinfection B. At the farthest point in the distribution system C. At the water plant D. Before filtration Measuring residual chlorine at the system’s end ensures adequate disinfection throughout the system. 66.Which condition favors biological nitrification in a distribution system? A. Low temperature B. High chlorine residual C. Warm temperatures and low disinfectant residuals D. High turbidity Nitrifying bacteria thrive in warm, low-chlorine conditions and convert ammonia to nitrate.
