Page 1 of 32
Water Treatment OIT Test 2026 – Operator-in-Training
(OIT) Water & Wastewater Operations – Complete Exam
Questions and Answers Study Guide
Introduction
This document contains a comprehensive collection of Water
Treatment Operator-in-Training (OIT) exam questions and
answers covering water distribution, wastewater treatment,
hydraulics, safety procedures, disinfection, filtration,
coagulation, chlorination, regulations, and treatment plant
operations. It includes multiple-choice questions with
solutions as well as detailed explanatory questions and
answers related to core water treatment concepts and
operational practices.
The material serves as a broad exam preparation resource for
entry-level water and wastewater operators and reviews both
theoretical knowledge and practical operational
responsibilities. It also covers regulatory compliance,
laboratory testing, process control, and public health
protection topics.
Exam Questions and Answers
When flushing a water main, operators should ensure that the
pressure in nearby areas does not drop below _______.
a) 60 kPa
b) 140 kPa
,Page 2 of 32
c) 350 kPa
d) 550 kPa --- correct precise answer ---b) 140 kPa
Which of the following best describes the largest volume of
water a distribution system would normally supply during a
day?
a) minimum demand (L/hour)
b) average demand (L/hour)
c) peak demand (L/hour)
d) average demand per person (L/hour/person) --- correct
precise answer ---c) peak demand (L/hour)
Distribution lines are flushed periodically to:
a) increase water pressure in the system
b) reduce the risk of water hammer
c) ensure that chlorine does not accumulate in pipes
d) remove deposits from the pipeline --- correct precise
answer ---d) remove deposits from the pipeline
What is NOT one of the main purposes of distribution storage?
a) to help satisfy peak demand
b) to allow for a uniform water treatment and pumping rate
c) to provide water for firefighting needs
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d) to store a large volume of water for long periods of time ---
correct precise answer ---d) to store a large volume of water
for long periods of time
What is the name of the valve which connects the customer's
service line to the municipal water line?
a) bypass valve
b) control flume
c) curb stop
d) check valve --- correct precise answer ---c) curb stop
In an activated sludge process, some of the sludge collected in
the secondary sedimentation tank is returned to the _______
to maintain the mass of the mixed liquor.
a) grit channel
b) aeration tank
c) primary sedimentation tank
d) digester --- correct precise answer ---b) aeration tank
Why does untreated sewage cause serious problems to
streams and lakes?
a) sewage will deplete the water of oxygen required by fish
and other animals
b) sewage creates unpleasant odours for water animals
c) sewage decreases the temperature of the water
, Page 4 of 32
d) sewage will decrease the amount of nutrients in the water -
-- correct precise answer ---a) sewage will deplete the water
of oxygen required by fish and other animals
A higher than normal BOD in the wastewater entering a
conventional wastewater treatment plant will most likely
have the greatest effect on which of the following processes?
a) grit removal
b) primary clarification
c) activated sludge
d) secondary clarification --- correct precise answer ---c)
activated sludge
Which of the following devices is used to measure the flow of
wastewater in an open channel?
a) comminutor
b) compactor
c) parshall flume
d) sluice gate --- correct precise answer ---c) parshall flume
Which of the following is a correct order of processes within a
conventional activated sludge treatment facility?
a) grit channel, aeration tank, primary sedimentation,
secondary sedimentation
Water Treatment OIT Test 2026 – Operator-in-Training
(OIT) Water & Wastewater Operations – Complete Exam
Questions and Answers Study Guide
Introduction
This document contains a comprehensive collection of Water
Treatment Operator-in-Training (OIT) exam questions and
answers covering water distribution, wastewater treatment,
hydraulics, safety procedures, disinfection, filtration,
coagulation, chlorination, regulations, and treatment plant
operations. It includes multiple-choice questions with
solutions as well as detailed explanatory questions and
answers related to core water treatment concepts and
operational practices.
The material serves as a broad exam preparation resource for
entry-level water and wastewater operators and reviews both
theoretical knowledge and practical operational
responsibilities. It also covers regulatory compliance,
laboratory testing, process control, and public health
protection topics.
Exam Questions and Answers
When flushing a water main, operators should ensure that the
pressure in nearby areas does not drop below _______.
a) 60 kPa
b) 140 kPa
,Page 2 of 32
c) 350 kPa
d) 550 kPa --- correct precise answer ---b) 140 kPa
Which of the following best describes the largest volume of
water a distribution system would normally supply during a
day?
a) minimum demand (L/hour)
b) average demand (L/hour)
c) peak demand (L/hour)
d) average demand per person (L/hour/person) --- correct
precise answer ---c) peak demand (L/hour)
Distribution lines are flushed periodically to:
a) increase water pressure in the system
b) reduce the risk of water hammer
c) ensure that chlorine does not accumulate in pipes
d) remove deposits from the pipeline --- correct precise
answer ---d) remove deposits from the pipeline
What is NOT one of the main purposes of distribution storage?
a) to help satisfy peak demand
b) to allow for a uniform water treatment and pumping rate
c) to provide water for firefighting needs
,Page 3 of 32
d) to store a large volume of water for long periods of time ---
correct precise answer ---d) to store a large volume of water
for long periods of time
What is the name of the valve which connects the customer's
service line to the municipal water line?
a) bypass valve
b) control flume
c) curb stop
d) check valve --- correct precise answer ---c) curb stop
In an activated sludge process, some of the sludge collected in
the secondary sedimentation tank is returned to the _______
to maintain the mass of the mixed liquor.
a) grit channel
b) aeration tank
c) primary sedimentation tank
d) digester --- correct precise answer ---b) aeration tank
Why does untreated sewage cause serious problems to
streams and lakes?
a) sewage will deplete the water of oxygen required by fish
and other animals
b) sewage creates unpleasant odours for water animals
c) sewage decreases the temperature of the water
, Page 4 of 32
d) sewage will decrease the amount of nutrients in the water -
-- correct precise answer ---a) sewage will deplete the water
of oxygen required by fish and other animals
A higher than normal BOD in the wastewater entering a
conventional wastewater treatment plant will most likely
have the greatest effect on which of the following processes?
a) grit removal
b) primary clarification
c) activated sludge
d) secondary clarification --- correct precise answer ---c)
activated sludge
Which of the following devices is used to measure the flow of
wastewater in an open channel?
a) comminutor
b) compactor
c) parshall flume
d) sluice gate --- correct precise answer ---c) parshall flume
Which of the following is a correct order of processes within a
conventional activated sludge treatment facility?
a) grit channel, aeration tank, primary sedimentation,
secondary sedimentation
