ILLINOIS CLASS C WATER EXAM 180 QUESTIONS &
CORRECT ANSWERS LATEST 2026/2027
What is the main reason for adding fluoride ion to drinking water? - ANSWER-
Reduce tooth decay
If an Illinois water supply fluoridates, the fluoride ion concentration in all of the
distribution system should be (in mg/L) : - ANSWER-0.7
What does a saturator feed? - ANSWER-Sodium fluoride solution
The fluoride chemical that is delivered to the treatment plant as a liquid is? -
ANSWER-H2SiF6 (hydrofluosilicic acid)
Which F chemical is required to have a free chlorine residual of 10mg/L
maintained in its solution? - ANSWER-Dry
Which chemical should NOT have a free chlorine residual of 10mg/L maintained
in its solution? - ANSWER-H2SiF6 (hydrofluosilicic acid)
Which fluoridation chemical gives off toxic fumes that will etch glass and may
cause damage the the operator's lungs? - ANSWER-H2SiF6 (hydrofluosilicic acid)
What is the colorimetric method for chlorine residual testing in Illinois called? -
ANSWER-Dpd method
,Which chlorine residual is most likely to cause taste and order problems? -
ANSWER-Dichlorimine
Centrifugal pumps should be started with the discharge valve in which position? -
ANSWER-Closed
For bacteria contamination, if repeat samples are required, what time frame should
they be taken? - ANSWER-Within 24 hours
When superchlorinating a storage tank or water main, the minimum residual
chlorine after 24 hours contact time should be? - ANSWER-25 mg/L
For most centrifugal pumps, if the total dynamic head decreased, the pump will
pump at a faster or slower rate in gpm? - ANSWER-Faster
What substances that will decrease in total amount as water ph increases? -
ANSWER-Hypochlorous Acid
What is used to convert liquid chlorine to chlorine to chlorine gas? - ANSWER-An
evaporator
What substance combines with leaking chlorine gas to form a white smoke? -
ANSWER-Ammonia Vapor
Positive Langelier Index can be produced by adding what? - ANSWER-Caustic
soda
A finished water with a negative Langelier index may be - ANSWER-Corrosive
, High trihalomethane levels may cause - ANSWER-Cancer
Solutions made from dry fluoride chemicals are required to contain how much of a
free chlorine residual? - ANSWER-10mg/L
How should gas chlorination equipment be stored? - ANSWER-Isolated in a room
separate from the rest of the plant.
What does the rotameter tube of a gas chlorinator indicate? - ANSWER-Chlorine
feed in lbs per 24 hours
Which chlorine residual will last the longest time in the distribution system? -
ANSWER-Combined
What chlorine residual contains hypochlorous acid and hypochlorite acid? -
ANSWER-Free chlorine
Chloramine is another name for what? - ANSWER-Combined chlorine
What is the minimum combined chlorine residual required throughout a water
distribution system in mg/L? - ANSWER-1.0 mg/L
After addition of the powdered test reagent, the free chlorine residual should be
determined within what time limit? - ANSWER-Within 1 minute
Chlorine dosage is equal to what? - ANSWER-Chlorine demand + Chlorine
residual
CORRECT ANSWERS LATEST 2026/2027
What is the main reason for adding fluoride ion to drinking water? - ANSWER-
Reduce tooth decay
If an Illinois water supply fluoridates, the fluoride ion concentration in all of the
distribution system should be (in mg/L) : - ANSWER-0.7
What does a saturator feed? - ANSWER-Sodium fluoride solution
The fluoride chemical that is delivered to the treatment plant as a liquid is? -
ANSWER-H2SiF6 (hydrofluosilicic acid)
Which F chemical is required to have a free chlorine residual of 10mg/L
maintained in its solution? - ANSWER-Dry
Which chemical should NOT have a free chlorine residual of 10mg/L maintained
in its solution? - ANSWER-H2SiF6 (hydrofluosilicic acid)
Which fluoridation chemical gives off toxic fumes that will etch glass and may
cause damage the the operator's lungs? - ANSWER-H2SiF6 (hydrofluosilicic acid)
What is the colorimetric method for chlorine residual testing in Illinois called? -
ANSWER-Dpd method
,Which chlorine residual is most likely to cause taste and order problems? -
ANSWER-Dichlorimine
Centrifugal pumps should be started with the discharge valve in which position? -
ANSWER-Closed
For bacteria contamination, if repeat samples are required, what time frame should
they be taken? - ANSWER-Within 24 hours
When superchlorinating a storage tank or water main, the minimum residual
chlorine after 24 hours contact time should be? - ANSWER-25 mg/L
For most centrifugal pumps, if the total dynamic head decreased, the pump will
pump at a faster or slower rate in gpm? - ANSWER-Faster
What substances that will decrease in total amount as water ph increases? -
ANSWER-Hypochlorous Acid
What is used to convert liquid chlorine to chlorine to chlorine gas? - ANSWER-An
evaporator
What substance combines with leaking chlorine gas to form a white smoke? -
ANSWER-Ammonia Vapor
Positive Langelier Index can be produced by adding what? - ANSWER-Caustic
soda
A finished water with a negative Langelier index may be - ANSWER-Corrosive
, High trihalomethane levels may cause - ANSWER-Cancer
Solutions made from dry fluoride chemicals are required to contain how much of a
free chlorine residual? - ANSWER-10mg/L
How should gas chlorination equipment be stored? - ANSWER-Isolated in a room
separate from the rest of the plant.
What does the rotameter tube of a gas chlorinator indicate? - ANSWER-Chlorine
feed in lbs per 24 hours
Which chlorine residual will last the longest time in the distribution system? -
ANSWER-Combined
What chlorine residual contains hypochlorous acid and hypochlorite acid? -
ANSWER-Free chlorine
Chloramine is another name for what? - ANSWER-Combined chlorine
What is the minimum combined chlorine residual required throughout a water
distribution system in mg/L? - ANSWER-1.0 mg/L
After addition of the powdered test reagent, the free chlorine residual should be
determined within what time limit? - ANSWER-Within 1 minute
Chlorine dosage is equal to what? - ANSWER-Chlorine demand + Chlorine
residual
