AWWA Operational Efficiency and Maintenance 2 — Questions and Answers
Question 1: What is the primary purpose of a valve exercising program in a water distribution system?
- To increase water pressure throughout the system
- To ensure valves operate properly and can be fully opened or closed when needed (Correct answer)
- To reduce the number of valves required in the system
- To improve water quality by circulating stagnant water
Correct answer: To ensure valves operate properly and can be fully opened or closed when needed
Regular valve exercising ensures valves remain operational and can be quickly isolated during emergencies or repairs.
Question 2: Which performance indicator best measures the effectiveness of a water main flushing program?
- Gallons flushed per day
- Turbidity and residual chlorine levels after flushing (Correct answer)
- Number of hydrants used during flushing
- Duration of each flushing event
Correct answer: Turbidity and residual chlorine levels after flushing
Turbidity and residual chlorine measurements confirm that flushing has removed sediment and restored adequate disinfectant levels.
Question 3: What does AWWA recommend as the maximum allowable unaccounted-for water (non-revenue water) percentage for a well-managed utility?
- 5%
- 10% (Correct answer)
- 15%
- 25%
Correct answer: 10%
AWWA guidelines suggest that utilities strive to keep non-revenue water below 10% of total system input volume.
Question 4: A pump's efficiency drops from 78% to 65% over one year of operation. What is the most likely cause?
- Increase in system demand
- Wear on impeller or wear rings (Correct answer)
- Higher static head in the system
- Reduced motor voltage
Correct answer: Wear on impeller or wear rings
Mechanical wear on pump impellers and wear rings increases clearances, reducing hydraulic efficiency over time.
Question 5: When evaluating energy efficiency, what does the term 'wire-to-water efficiency' refer to?
- The efficiency of converting electrical energy at the meter to useful hydraulic output (Correct answer)
- The energy lost in transmission lines to the pump station
- The ratio of pumping hours to total operating hours
- The voltage drop across pump motor terminals
Correct answer: The efficiency of converting electrical energy at the meter to useful hydraulic output
Wire-to-water efficiency measures the overall system efficiency from electrical input power to hydraulic power delivered to the water.
Question 6: Which maintenance strategy involves replacing equipment components based on age or usage intervals, regardless of current condition?
- Corrective maintenance
- Predictive maintenance
- Preventive maintenance (Correct answer)
- Reliability-centered maintenance
Correct answer: Preventive maintenance
Preventive maintenance follows scheduled intervals (time-based or usage-based) to replace parts before failure occurs.
Question 7: What is the recommended minimum free chlorine residual at the far ends of a distribution system per AWWA guidelines?
- 0.1 mg/L (Correct answer)
- 0.2 mg/L
- 0.5 mg/L
- 1.0 mg/L
Correct answer: 0.1 mg/L
AWWA recommends maintaining a minimum detectable free chlorine residual of at least 0.2 mg/L, though the EPA minimum detectable standard is 0.2 mg/L; 0.1 mg/L is often cited as the absolute floor for distribution system endpoints.
AWWA Operational Efficiency and Maintenance 2
What is the primary purpose of a valve exercising program in a water distribution system?