D2 WATER DISTRIBUTION OPERATOR PRACTICE
EXAM (CALIFORNIA) 200 Multiple Choice Questions with
Correct Answers & Explanations.
Page 1
,Q1. In a large California water distribution system, a pressure-sustaining valve is
installed upstream of a pressure-reducing valve. During a fire flow event, the
downstream demand increases dramatically. Which of the following best describes
the combined hydraulic behavior?
A. The pressure-sustaining valve modulates to maintain a set upstream pressure,
potentially reducing flow to the pressure-reducing valve, which then may deliver lower
pressure downstream.
B. The pressure-reducing valve fully opens, and the pressure-sustaining valve closes to
isolate the downstream network, preventing pressure drop.
C. Both valves operate independently; the pressure-sustaining valve maintains
downstream pressure while the pressure-reducing valve controls upstream pressure.
D. The pressure-sustaining valve opens fully to allow maximum flow, and the
pressure-reducing valve maintains a constant downstream pressure regardless of
upstream conditions.
Correct Answer: A. The pressure-sustaining valve modulates to maintain a set
upstream pressure, potentially reducing flow to the pressure-reducing valve, which
then may deliver lower pressure downstream.
Rationale: A pressure-sustaining valve maintains a minimum pressure at its upstream side
by throttling flow. During high downstream demand, the pressure-reducing valve tries to
pass more flow, which can cause upstream pressure to drop. The PSV then throttles to
sustain its setpoint, limiting flow to the PRV, which consequently cannot maintain
downstream pressure. This interaction is critical for fire flow scenarios.
Why Wrong:
B - The PSV does not close to isolate; it throttles to sustain upstream pressure, and the
PRV does not fully open in a controlled manner.
C - The PSV controls upstream pressure, not downstream; the PRV controls
downstream pressure, not upstream.
D - The PSV does not open fully; it modulates to sustain upstream pressure, and the
PRV cannot maintain downstream pressure if upstream pressure falls below its
setpoint.
Reference: AWWA M51, Air Release, Air/Vacuum, and Combination Air Valves; and M22,
Sizing Water Service Lines and Meters.
Q2. A water utility plans to install a new 12-inch ductile iron pipe in a trench with a
maximum depth of 8 feet. Using the California trench loading tables, the calculated
earth load is 12,000 lb/ft. The pipe has a laying length of 20 feet and a safety factor of
1.5. What is the minimum required three-edge bearing strength (in lb/ft) for the pipe?
A. 18,000
B. 15,000
C. 9,000
Page 2
, D. 24,000
Correct Answer: A. 18,000
Rationale: The required three-edge bearing strength is calculated as: (earth load × safety
factor) / laying length. Here, (12,000 lb/ft × 1.5) = 18,000 lb/ft. This value must be met or
exceeded by the pipe's minimum strength per ASTM C14 or C76.
Why Wrong:
B - 15,000 lb/ft would result from using a safety factor of 1.25, not 1.5.
C - 9,000 lb/ft ignores the safety factor and incorrectly uses only the earth load.
D - 24,000 lb/ft results from multiplying the earth load by 2.0, an overly conservative
factor not specified.
Reference: AWWA M23, PVC Pipe - Design and Installation; and ASTM C14/C76
standards.
Q3. A water distribution system has a storage tank with a water level that fluctuates.
The SCADA system records a pressure of 60 psi at a point 120 feet below the tank's
overflow. If the tank diameter is 30 feet and the water level is 10 feet below overflow,
what is the static pressure (in psi) at that point?
A. 52.0
B. 47.6
C. 60.0
D. 55.0
Correct Answer: B. 47.6
Rationale: Static pressure = (head in feet) × 0.433 psi/ft. The head is the vertical distance
from the water surface to the point: (120 ft - 10 ft) = 110 ft. Thus, pressure = 110 × 0.433
= 47.63 psi. The tank diameter is irrelevant.
Why Wrong:
A - 52.0 psi would correspond to a head of 120 ft, ignoring the water level below
overflow.
C - 60 psi is the recorded pressure, which is not the static pressure calculated from the
given head.
D - 55.0 psi would result from using a head of 127 ft, a miscalculation.
Reference: AWWA M31, Distribution System Requirements for Fire Protection.
Q4. A water utility is required to comply with the California Waterworks Standards
(CCR Title 22). Which of the following cross-connection control measures is most
directly mandated for all public water systems?
A. Annual inspection of all service connections by a certified cross-connection control
specialist.
B. Installation of a reduced pressure zone (RPZ) assembly at every residential service
Page 3
, connection.
C. Implementation of a cross-connection control program that includes survey and
enforcement of backflow prevention requirements.
D. Mandatory use of dual check valves at all commercial and industrial connections.
Correct Answer: C. Implementation of a cross-connection control program that
includes survey and enforcement of backflow prevention requirements.
Rationale: CCR Title 22 requires public water systems to establish and maintain a
cross-connection control program, including surveys and enforcement. It does not
mandate specific devices at all connections, nor annual inspections by a certified specialist
as a blanket requirement, though these are common practices.
Why Wrong:
A - Annual inspections are not universally mandated; program specifics vary by risk
assessment.
B - RPZ assemblies are required only for high-hazard connections, not all residential
services.
D - Dual check valves are not mandated for all commercial/industrial connections;
requirements depend on the degree of hazard.
Reference: California Code of Regulations, Title 22, Chapter 16, Article 4.
Q5. A water sample collected from a dead-end main in a distribution system tests
positive for coliform bacteria. Which of the following is the most likely cause and the
most appropriate immediate response?
A. Inadequate chlorine residual due to stagnation; flush the line and resample.
B. Cross-connection with a sewage line; issue a boil water advisory immediately.
C. Biofilm growth on pipe walls; increase chlorine dosage permanently.
D. Contaminated sampling tap; disinfect the tap and resample.
Correct Answer: A. Inadequate chlorine residual due to stagnation; flush the line and
resample.
Rationale: Dead-end mains commonly experience stagnation, leading to chlorine residual
depletion and bacterial regrowth. Flushing removes stagnant water and restores
disinfectant residual, then resampling confirms resolution. Immediate boil water advisory
is not warranted without evidence of a cross-connection or confirmed contamination.
Why Wrong:
B - A boil water advisory is premature without evidence of a cross-connection or
pathogen presence; flushing is the first step.
C - Biofilm may be present, but simply increasing chlorine is not the immediate
response; flushing is required to remove the contaminated water.
D - While a contaminated tap is possible, the dead-end location strongly suggests
stagnation; flushing is the standard first response.
Page 4
EXAM (CALIFORNIA) 200 Multiple Choice Questions with
Correct Answers & Explanations.
Page 1
,Q1. In a large California water distribution system, a pressure-sustaining valve is
installed upstream of a pressure-reducing valve. During a fire flow event, the
downstream demand increases dramatically. Which of the following best describes
the combined hydraulic behavior?
A. The pressure-sustaining valve modulates to maintain a set upstream pressure,
potentially reducing flow to the pressure-reducing valve, which then may deliver lower
pressure downstream.
B. The pressure-reducing valve fully opens, and the pressure-sustaining valve closes to
isolate the downstream network, preventing pressure drop.
C. Both valves operate independently; the pressure-sustaining valve maintains
downstream pressure while the pressure-reducing valve controls upstream pressure.
D. The pressure-sustaining valve opens fully to allow maximum flow, and the
pressure-reducing valve maintains a constant downstream pressure regardless of
upstream conditions.
Correct Answer: A. The pressure-sustaining valve modulates to maintain a set
upstream pressure, potentially reducing flow to the pressure-reducing valve, which
then may deliver lower pressure downstream.
Rationale: A pressure-sustaining valve maintains a minimum pressure at its upstream side
by throttling flow. During high downstream demand, the pressure-reducing valve tries to
pass more flow, which can cause upstream pressure to drop. The PSV then throttles to
sustain its setpoint, limiting flow to the PRV, which consequently cannot maintain
downstream pressure. This interaction is critical for fire flow scenarios.
Why Wrong:
B - The PSV does not close to isolate; it throttles to sustain upstream pressure, and the
PRV does not fully open in a controlled manner.
C - The PSV controls upstream pressure, not downstream; the PRV controls
downstream pressure, not upstream.
D - The PSV does not open fully; it modulates to sustain upstream pressure, and the
PRV cannot maintain downstream pressure if upstream pressure falls below its
setpoint.
Reference: AWWA M51, Air Release, Air/Vacuum, and Combination Air Valves; and M22,
Sizing Water Service Lines and Meters.
Q2. A water utility plans to install a new 12-inch ductile iron pipe in a trench with a
maximum depth of 8 feet. Using the California trench loading tables, the calculated
earth load is 12,000 lb/ft. The pipe has a laying length of 20 feet and a safety factor of
1.5. What is the minimum required three-edge bearing strength (in lb/ft) for the pipe?
A. 18,000
B. 15,000
C. 9,000
Page 2
, D. 24,000
Correct Answer: A. 18,000
Rationale: The required three-edge bearing strength is calculated as: (earth load × safety
factor) / laying length. Here, (12,000 lb/ft × 1.5) = 18,000 lb/ft. This value must be met or
exceeded by the pipe's minimum strength per ASTM C14 or C76.
Why Wrong:
B - 15,000 lb/ft would result from using a safety factor of 1.25, not 1.5.
C - 9,000 lb/ft ignores the safety factor and incorrectly uses only the earth load.
D - 24,000 lb/ft results from multiplying the earth load by 2.0, an overly conservative
factor not specified.
Reference: AWWA M23, PVC Pipe - Design and Installation; and ASTM C14/C76
standards.
Q3. A water distribution system has a storage tank with a water level that fluctuates.
The SCADA system records a pressure of 60 psi at a point 120 feet below the tank's
overflow. If the tank diameter is 30 feet and the water level is 10 feet below overflow,
what is the static pressure (in psi) at that point?
A. 52.0
B. 47.6
C. 60.0
D. 55.0
Correct Answer: B. 47.6
Rationale: Static pressure = (head in feet) × 0.433 psi/ft. The head is the vertical distance
from the water surface to the point: (120 ft - 10 ft) = 110 ft. Thus, pressure = 110 × 0.433
= 47.63 psi. The tank diameter is irrelevant.
Why Wrong:
A - 52.0 psi would correspond to a head of 120 ft, ignoring the water level below
overflow.
C - 60 psi is the recorded pressure, which is not the static pressure calculated from the
given head.
D - 55.0 psi would result from using a head of 127 ft, a miscalculation.
Reference: AWWA M31, Distribution System Requirements for Fire Protection.
Q4. A water utility is required to comply with the California Waterworks Standards
(CCR Title 22). Which of the following cross-connection control measures is most
directly mandated for all public water systems?
A. Annual inspection of all service connections by a certified cross-connection control
specialist.
B. Installation of a reduced pressure zone (RPZ) assembly at every residential service
Page 3
, connection.
C. Implementation of a cross-connection control program that includes survey and
enforcement of backflow prevention requirements.
D. Mandatory use of dual check valves at all commercial and industrial connections.
Correct Answer: C. Implementation of a cross-connection control program that
includes survey and enforcement of backflow prevention requirements.
Rationale: CCR Title 22 requires public water systems to establish and maintain a
cross-connection control program, including surveys and enforcement. It does not
mandate specific devices at all connections, nor annual inspections by a certified specialist
as a blanket requirement, though these are common practices.
Why Wrong:
A - Annual inspections are not universally mandated; program specifics vary by risk
assessment.
B - RPZ assemblies are required only for high-hazard connections, not all residential
services.
D - Dual check valves are not mandated for all commercial/industrial connections;
requirements depend on the degree of hazard.
Reference: California Code of Regulations, Title 22, Chapter 16, Article 4.
Q5. A water sample collected from a dead-end main in a distribution system tests
positive for coliform bacteria. Which of the following is the most likely cause and the
most appropriate immediate response?
A. Inadequate chlorine residual due to stagnation; flush the line and resample.
B. Cross-connection with a sewage line; issue a boil water advisory immediately.
C. Biofilm growth on pipe walls; increase chlorine dosage permanently.
D. Contaminated sampling tap; disinfect the tap and resample.
Correct Answer: A. Inadequate chlorine residual due to stagnation; flush the line and
resample.
Rationale: Dead-end mains commonly experience stagnation, leading to chlorine residual
depletion and bacterial regrowth. Flushing removes stagnant water and restores
disinfectant residual, then resampling confirms resolution. Immediate boil water advisory
is not warranted without evidence of a cross-connection or confirmed contamination.
Why Wrong:
B - A boil water advisory is premature without evidence of a cross-connection or
pathogen presence; flushing is the first step.
C - Biofilm may be present, but simply increasing chlorine is not the immediate
response; flushing is required to remove the contaminated water.
D - While a contaminated tap is possible, the dead-end location strongly suggests
stagnation; flushing is the standard first response.
Page 4
