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MINNESOTA DRINKING WATER OPERATOR CLASS D
EXAM – 2026/2027 COMPLETE (140) CURRENT TESTING
QUESTIONS AND CORRECT ANSWERS WITH DETAILED
RATIONALES.
DRINKING
Prepare for the Minnesota Drinking Water Operator Class D Exam with this focused
practice resource designed to support your certification preparation. It features exam-
style questions covering small water system operations, groundwater supply
management, basic disinfection practices, water sampling and testing protocols,
pump operation and maintenance, and Minnesota Department of Health (MDH) Safe
Drinking Water Act regulations. An ideal study aid for water utility operators, public
works technicians, and system superintendents looking to reinforce essential water
treatment principles and pass their state licensing exam.
MULTIPLE CHOICE.
SECTION 1: WATER SOURCES, HYDROLOGY, AND PUBLIC WATER
SYSTEMS (Questions 1-20)
1. According to the Safe Drinking Water Act, what is the basic definition of
a public water supply system?
A) Any water system that serves at least 10 service connections
B) Any water system that supplies water for human consumption that serves
15 service connections or over 25 persons for over 60 days a year
C) Any water system that serves a municipality
D) Any water system that treats surface water
Answer: B
Rationale: Under the Safe Drinking Water Act, a public water supply
system is defined as any system that supplies water for human
consumption and serves at least 15 service connections or 25 or more
people for at least 60 days per year.
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2. What federal law regulates public water supplies?
A) Clean Water Act
B) Safe Drinking Water Act (SDWA)
C) Resource Conservation and Recovery Act
D) Toxic Substances Control Act
Answer: B
Rationale: The Safe Drinking Water Act (SDWA) is the primary federal law
that regulates public water supplies and sets standards for drinking water
quality.
3. Which agency regulates drinking water standards in Minnesota?
A) Minnesota Department of Transportation
B) Minnesota Department of Agriculture
C) Minnesota Department of Health (MDH)
D) Environmental Protection Agency only
Answer: C
Rationale: The Minnesota Department of Health (MDH) regulates public
drinking water systems in Minnesota.
4. What causes water to move through pores in soil and rocks?
A) Capillary action
B) Gravity
C) Osmosis
D) Atmospheric pressure
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Answer: B
Rationale: Gravity is the primary force that causes water to move
downward through pores in soil and rocks, recharging groundwater
aquifers.
5. Which source of water has the greatest natural protection from
bacterial contamination?
A) Surface water from a lake
B) River water
C) Deep well in gravel
D) Rainwater collection
Answer: C
Rationale: Deep wells in gravel provide the greatest natural protection
from bacterial contamination because the soil and rock layers filter out
bacteria and other contaminants.
6. What is the minimum distance a community public water supply well
must be from any contamination source?
A) 25 feet
B) 50 feet
C) 100 feet
D) 150 feet
Answer: B
Rationale: Minnesota regulations require a minimum distance of 50 feet
between a community public water supply well and any contamination
source.
7. The two categories of water quality characteristics are:
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A) Physical and chemical
B) Biological and radiological
C) Organic and inorganic
D) Primary and secondary
Answer: A
Rationale: Water quality characteristics are divided into two main
categories: physical characteristics (such as temperature, turbidity, color,
taste, and odor) and chemical characteristics (such as pH, hardness, and
dissolved solids).
8. A well screen must be installed for which of the following?
A) Surface water intakes
B) Gravel-packed wells
C) All water supply wells
D) Storage tanks only
Answer: B
Rationale: Well screens are specifically required for gravel-packed wells
to prevent sand and gravel from entering the well while allowing water to
flow through.
9. The typical range of pH for groundwater is:
A) 4.0 to 5.5
B) 6.0 to 8.5
C) 7.0 to 9.0
D) 5.5 to 7.5
MINNESOTA DRINKING WATER OPERATOR CLASS D
EXAM – 2026/2027 COMPLETE (140) CURRENT TESTING
QUESTIONS AND CORRECT ANSWERS WITH DETAILED
RATIONALES.
DRINKING
Prepare for the Minnesota Drinking Water Operator Class D Exam with this focused
practice resource designed to support your certification preparation. It features exam-
style questions covering small water system operations, groundwater supply
management, basic disinfection practices, water sampling and testing protocols,
pump operation and maintenance, and Minnesota Department of Health (MDH) Safe
Drinking Water Act regulations. An ideal study aid for water utility operators, public
works technicians, and system superintendents looking to reinforce essential water
treatment principles and pass their state licensing exam.
MULTIPLE CHOICE.
SECTION 1: WATER SOURCES, HYDROLOGY, AND PUBLIC WATER
SYSTEMS (Questions 1-20)
1. According to the Safe Drinking Water Act, what is the basic definition of
a public water supply system?
A) Any water system that serves at least 10 service connections
B) Any water system that supplies water for human consumption that serves
15 service connections or over 25 persons for over 60 days a year
C) Any water system that serves a municipality
D) Any water system that treats surface water
Answer: B
Rationale: Under the Safe Drinking Water Act, a public water supply
system is defined as any system that supplies water for human
consumption and serves at least 15 service connections or 25 or more
people for at least 60 days per year.
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2. What federal law regulates public water supplies?
A) Clean Water Act
B) Safe Drinking Water Act (SDWA)
C) Resource Conservation and Recovery Act
D) Toxic Substances Control Act
Answer: B
Rationale: The Safe Drinking Water Act (SDWA) is the primary federal law
that regulates public water supplies and sets standards for drinking water
quality.
3. Which agency regulates drinking water standards in Minnesota?
A) Minnesota Department of Transportation
B) Minnesota Department of Agriculture
C) Minnesota Department of Health (MDH)
D) Environmental Protection Agency only
Answer: C
Rationale: The Minnesota Department of Health (MDH) regulates public
drinking water systems in Minnesota.
4. What causes water to move through pores in soil and rocks?
A) Capillary action
B) Gravity
C) Osmosis
D) Atmospheric pressure
, Page 3 of 55
Answer: B
Rationale: Gravity is the primary force that causes water to move
downward through pores in soil and rocks, recharging groundwater
aquifers.
5. Which source of water has the greatest natural protection from
bacterial contamination?
A) Surface water from a lake
B) River water
C) Deep well in gravel
D) Rainwater collection
Answer: C
Rationale: Deep wells in gravel provide the greatest natural protection
from bacterial contamination because the soil and rock layers filter out
bacteria and other contaminants.
6. What is the minimum distance a community public water supply well
must be from any contamination source?
A) 25 feet
B) 50 feet
C) 100 feet
D) 150 feet
Answer: B
Rationale: Minnesota regulations require a minimum distance of 50 feet
between a community public water supply well and any contamination
source.
7. The two categories of water quality characteristics are:
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A) Physical and chemical
B) Biological and radiological
C) Organic and inorganic
D) Primary and secondary
Answer: A
Rationale: Water quality characteristics are divided into two main
categories: physical characteristics (such as temperature, turbidity, color,
taste, and odor) and chemical characteristics (such as pH, hardness, and
dissolved solids).
8. A well screen must be installed for which of the following?
A) Surface water intakes
B) Gravel-packed wells
C) All water supply wells
D) Storage tanks only
Answer: B
Rationale: Well screens are specifically required for gravel-packed wells
to prevent sand and gravel from entering the well while allowing water to
flow through.
9. The typical range of pH for groundwater is:
A) 4.0 to 5.5
B) 6.0 to 8.5
C) 7.0 to 9.0
D) 5.5 to 7.5
