1|Page
ILLINOIS CLASS D WATER FINAL EXAM 2025/ 2026
ACTUAL EXAM COMPLETE EXAM QUESTIONS WITH
DETAILED VERIFIED ANSWERS WITH RATIONALES
/BRAND NEW!! /ALREADY GRADED A+|| LATEST
EXAM!!
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
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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
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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
ILLINOIS CLASS D WATER FINAL EXAM 2025/ 2026
ACTUAL EXAM COMPLETE EXAM QUESTIONS WITH
DETAILED VERIFIED ANSWERS WITH RATIONALES
/BRAND NEW!! /ALREADY GRADED A+|| LATEST
EXAM!!
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
,2|Page
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
, 3|Page
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
