Texas Class D Water Test
(Updated for 2026) Exam Prep Pack | A+ Questions
70+
& Verified Answers
VERIFIED ANSWERS
Question 1
Who is authorized to remove a lock and tag placed on a piece of equipment to isolate it for maintenance?
Correct Answer
Only the person who placed the lock and tag
Rationale:
This is correct because it aligns with the principle of accountability, where only the individual responsible for the lock and tag placement has
the authority to remove it, ensuring that maintenance is performed in a controlled and safe manner. By requiring the original person to remove
the lock and tag, there is a clear audit trail and accountability for ensuring the equipment is properly cleared for maintenance.
Question 2
In addition of an emergency residual pressure of 20 psi, what is the minimum normal operating pressure a public water
supply system should maintain?
Correct Answer
35 psi
Rationale:
The "40 psi" standard is often recommended as a minimum normal operating pressure for public water supply systems in the United States,
but this specific question may be referring to an older or specific standard that recommends a minimum pressure of 35 psi, taking into account
the emergency residual pressure of 20 psi. This is likely due to the fact that the total system pressure should be at least 35 psi to ensure
adequate flow and pressure for firefighting and other emergency purposes.
Question 3
What is the minimum distance separating installed water mains from any sewer lines or other possible contaminated lines?
Correct Answer
9 feet
Rationale:
The minimum distance required to separate water mains from contaminated lines is due to the potential for cross-contamination, where water
mains can become contaminated with pollutants or pathogens from other lines if they are too close. A separation distance of 9 feet is often
specified to provide a sufficient buffer zone, taking into account factors such as the size and layout of the underground infrastructure, to
prevent such cross-contamination and ensure the safety of the drinking water supply.
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,Question 4
What is the minimum distance required to separate grazing livestock and septic tanks from a public well?
Correct Answer
50 feet
Rationale:
The minimum distance required to separate grazing livestock and septic tanks from a public well is based on the risk of contamination from
pathogens and nutrients in animal waste and septic effluent, which can travel through the soil and infiltrate groundwater, posing a risk to public
health. By setting a minimum distance of 50 feet, this regulatory standard aims to protect the public well from potential contamination by
allowing sufficient time for the natural attenuation of pathogens and nutrients as they pass through the unsaturated zone.
Question 5
What color does the sample turn when the DPD reagent is added to water containing chlorine?
Correct Answer
Red
Rationale:
The DPD reagent is a chlorine test kit component that reacts with chlorine to form a colored compound. When the DPD reagent is added to
water containing chlorine, it forms a pink or red compound due to the reaction between the DPD and chlorine, allowing the presence and
concentration of chlorine to be visually determined.
Question 6
A system is operating at a flow rate of 2.2 MGD. A chlorine dose of 10 mg/L is required to maintain a disinfectant residual of
0.4 mg/L. Calculate the daily chlorine demand in pounds.
Correct Answer
176 pounds
Rationale:
The key concept in solving this problem is the difference between the chlorine dose required and the final chlorine residual, as the chlorine
dose minus the final chlorine residual represents the daily chlorine demand. By multiplying this difference (10 mg/L - 0.4 mg/L = 9.6 mg/L) by
the flow rate (2.2 MGD) and converting milligrams to pounds (1 mg/L = 8.34 lb/MG), the correct calculation of daily chlorine demand in pounds
can be determined.
Question 7
A tank with 1 foot of water above a pressure gauge at the bottom will register a reading of:
Correct Answer
0.433 psi
Rationale:
The key concept here is that water is essentially incompressible, meaning its density remains constant, and 1 foot of water exerts a pressure
equal to its weight per unit area. Since the weight of 1 foot of water is approximately 0.433 pounds per square inch (psi), the pressure gauge
will register this reading.
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, Question 8
Pipe and fittings used in public water systems may not contain more than ____% lead or solder and flux may not contain
more than ____% lead.
Correct Answer
0.25%, 0.2%
Rationale:
The regulations for public water systems are based on the Safe Drinking Water Act, which sets limits on lead levels in pipes and fittings to
protect public health. The specified limits of 0.25% lead in pipes and fittings and 0.2% lead in solder and flux are designed to minimize the risk
of lead contamination in drinking water, particularly for vulnerable populations such as children and pregnant women.
Question 9
Chlorine tablets (Calcium hypochlorite) should not come in contact with ________ based products due to the violent
reaction that will result.
Correct Answer
Petroleum
Rationale:
Calcium hypochlorite reacts violently with organic materials, such as petroleum, causing a rapid exothermic reaction due to the high heat of
combustion of the organic compound. This violent reaction is a result of the combination of the oxidizing agent, chlorine, and the fuel source,
organic materials found in petroleum-based products.
Question 10
How much does one gallon of water weigh?
Correct Answer
8.34 lbs
Rationale:
One gallon of water weighs 8.34 pounds due to the density of water, which is approximately 8.34 pounds per gallon, a value determined by the
mass of a gallon of water divided by its volume. This density is a fixed value because the mass of one gallon of water is equivalent to the mass
of one gallon of any liquid, as long as the temperature and pressure remain constant.
Question 11
After disinfecting a newly installed water main, bacteriological samples are required to be collected every ____ feet along
the new line.
Correct Answer
1,000
Rationale:
This question is based on a common standard in the water treatment industry, specifically the United States Environmental Protection Agency's
(EPA) guidelines for water distribution system sampling. The requirement to collect bacteriological samples every 1,000 feet along the new line
is intended to ensure an adequate number of samples are taken to accurately represent the water quality in the distribution system.
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(Updated for 2026) Exam Prep Pack | A+ Questions
70+
& Verified Answers
VERIFIED ANSWERS
Question 1
Who is authorized to remove a lock and tag placed on a piece of equipment to isolate it for maintenance?
Correct Answer
Only the person who placed the lock and tag
Rationale:
This is correct because it aligns with the principle of accountability, where only the individual responsible for the lock and tag placement has
the authority to remove it, ensuring that maintenance is performed in a controlled and safe manner. By requiring the original person to remove
the lock and tag, there is a clear audit trail and accountability for ensuring the equipment is properly cleared for maintenance.
Question 2
In addition of an emergency residual pressure of 20 psi, what is the minimum normal operating pressure a public water
supply system should maintain?
Correct Answer
35 psi
Rationale:
The "40 psi" standard is often recommended as a minimum normal operating pressure for public water supply systems in the United States,
but this specific question may be referring to an older or specific standard that recommends a minimum pressure of 35 psi, taking into account
the emergency residual pressure of 20 psi. This is likely due to the fact that the total system pressure should be at least 35 psi to ensure
adequate flow and pressure for firefighting and other emergency purposes.
Question 3
What is the minimum distance separating installed water mains from any sewer lines or other possible contaminated lines?
Correct Answer
9 feet
Rationale:
The minimum distance required to separate water mains from contaminated lines is due to the potential for cross-contamination, where water
mains can become contaminated with pollutants or pathogens from other lines if they are too close. A separation distance of 9 feet is often
specified to provide a sufficient buffer zone, taking into account factors such as the size and layout of the underground infrastructure, to
prevent such cross-contamination and ensure the safety of the drinking water supply.
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,Question 4
What is the minimum distance required to separate grazing livestock and septic tanks from a public well?
Correct Answer
50 feet
Rationale:
The minimum distance required to separate grazing livestock and septic tanks from a public well is based on the risk of contamination from
pathogens and nutrients in animal waste and septic effluent, which can travel through the soil and infiltrate groundwater, posing a risk to public
health. By setting a minimum distance of 50 feet, this regulatory standard aims to protect the public well from potential contamination by
allowing sufficient time for the natural attenuation of pathogens and nutrients as they pass through the unsaturated zone.
Question 5
What color does the sample turn when the DPD reagent is added to water containing chlorine?
Correct Answer
Red
Rationale:
The DPD reagent is a chlorine test kit component that reacts with chlorine to form a colored compound. When the DPD reagent is added to
water containing chlorine, it forms a pink or red compound due to the reaction between the DPD and chlorine, allowing the presence and
concentration of chlorine to be visually determined.
Question 6
A system is operating at a flow rate of 2.2 MGD. A chlorine dose of 10 mg/L is required to maintain a disinfectant residual of
0.4 mg/L. Calculate the daily chlorine demand in pounds.
Correct Answer
176 pounds
Rationale:
The key concept in solving this problem is the difference between the chlorine dose required and the final chlorine residual, as the chlorine
dose minus the final chlorine residual represents the daily chlorine demand. By multiplying this difference (10 mg/L - 0.4 mg/L = 9.6 mg/L) by
the flow rate (2.2 MGD) and converting milligrams to pounds (1 mg/L = 8.34 lb/MG), the correct calculation of daily chlorine demand in pounds
can be determined.
Question 7
A tank with 1 foot of water above a pressure gauge at the bottom will register a reading of:
Correct Answer
0.433 psi
Rationale:
The key concept here is that water is essentially incompressible, meaning its density remains constant, and 1 foot of water exerts a pressure
equal to its weight per unit area. Since the weight of 1 foot of water is approximately 0.433 pounds per square inch (psi), the pressure gauge
will register this reading.
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, Question 8
Pipe and fittings used in public water systems may not contain more than ____% lead or solder and flux may not contain
more than ____% lead.
Correct Answer
0.25%, 0.2%
Rationale:
The regulations for public water systems are based on the Safe Drinking Water Act, which sets limits on lead levels in pipes and fittings to
protect public health. The specified limits of 0.25% lead in pipes and fittings and 0.2% lead in solder and flux are designed to minimize the risk
of lead contamination in drinking water, particularly for vulnerable populations such as children and pregnant women.
Question 9
Chlorine tablets (Calcium hypochlorite) should not come in contact with ________ based products due to the violent
reaction that will result.
Correct Answer
Petroleum
Rationale:
Calcium hypochlorite reacts violently with organic materials, such as petroleum, causing a rapid exothermic reaction due to the high heat of
combustion of the organic compound. This violent reaction is a result of the combination of the oxidizing agent, chlorine, and the fuel source,
organic materials found in petroleum-based products.
Question 10
How much does one gallon of water weigh?
Correct Answer
8.34 lbs
Rationale:
One gallon of water weighs 8.34 pounds due to the density of water, which is approximately 8.34 pounds per gallon, a value determined by the
mass of a gallon of water divided by its volume. This density is a fixed value because the mass of one gallon of water is equivalent to the mass
of one gallon of any liquid, as long as the temperature and pressure remain constant.
Question 11
After disinfecting a newly installed water main, bacteriological samples are required to be collected every ____ feet along
the new line.
Correct Answer
1,000
Rationale:
This question is based on a common standard in the water treatment industry, specifically the United States Environmental Protection Agency's
(EPA) guidelines for water distribution system sampling. The requirement to collect bacteriological samples every 1,000 feet along the new line
is intended to ensure an adequate number of samples are taken to accurately represent the water quality in the distribution system.
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