Level 2 Water Distribution Exam Prep (50 Questions)
1. What is the typical operating pressure range in a municipal water distribution system?
40–100 psi (275–690 kPa).
2. What is the minimum chlorine residual required at the extreme ends of a distribution system in Ontario?
0.05 mg/L free chlorine.
3. What is the maximum allowable turbidity in treated drinking water under Ontario regulations?
1.0 NTU (with a target of 0.3 NTU for optimized systems).
4. If a pipe is 12 inches in diameter, what is its cross-sectional area?
Area = π × (d/2)² = 3.14 × (0.5 ft)² = 0.785 ft².
5. What is the main purpose of pressure zones in a water distribution system?
To maintain adequate pressure across varying elevations in the service area.
6. What is the main advantage of unidirectional flushing over conventional flushing?
Achieves higher velocities for pipe cleaning while using less water.
7. What is the Hazen-Williams formula used for?
To calculate head loss (friction loss) in water distribution pipes.
8. What does a water hammer arrestor prevent?
Damage caused by sudden pressure surges from rapid valve or pump operation.
9. A pump delivers 800 gpm at 60 psi. What is the total dynamic head?
TDH = (60 psi × 2.31) = 139 ft of head.
10. What is the primary purpose of an elevated water storage tank?
To provide pressure through elevation and store water for peak demand and fire protection.
11. What is a cross-connection?
A physical connection between potable water and a source of contamination.
12. What is the purpose of a backflow preventer?
To prevent contaminants from entering the potable water system due to backpressure or back-siphonage.
13. What is the recommended fire flow for residential areas?
Typically 500–1000 gpm for 2 hours (depends on local codes).
14. If flow is 1,000 gpm in an 8-inch pipe, what is the velocity?
Q = V × A → V = Q / A. Area = 0.349 ft².
Q = 133.7 ft³/s → V = 383 ft/s ÷ 0.349 ≈ 5.5 ft/s.
15. What does SCADA stand for?
Supervisory Control and Data Acquisition.
16. What is the maximum day demand (MDD)?
The highest average daily demand of water in a given year.
17. What is the difference between static head and dynamic head?
Static head = elevation difference.
Dynamic head = static head + friction and velocity losses.
18. What type of hydrant is most commonly used in Canada?
Dry barrel hydrants (suited for freezing conditions).
19. What is the typical spacing of hydrants in commercial areas?
About 90 m (300 ft), varies by code.
20. What is non-revenue water (NRW)?
Water that is produced but not billed due to leaks, theft, or metering inaccuracies.
21. What is the function of a pressure reducing valve (PRV)?
To regulate and lower downstream pressure to safe levels.
22. What is the function of a pressure sustaining valve?
To maintain upstream pressure while allowing flow downstream.
23. What is the function of an altitude valve on a tank?
To automatically control tank filling and prevent overflow.
24. What is the primary cause of discoloured water complaints?
Iron and manganese deposits stirred up by flow changes.
25. What is the safe minimum oxygen level in a confined space?
19.5% oxygen.
26. What is the maximum safe working level for H₂S gas?
10 ppm (OSHA limit).
27. What is the typical chlorine demand in a distribution system?
0.5–2.0 mg/L depending on water quality and system conditions.
28. What is the first step in repairing a water main break?
Isolate the section by closing valves and notifying affected customers.
29. After repairing a water main, what must be done before putting it back into service?
Flush, disinfect, and take bacteriological samples.
30. What is a valve exercising program?
A maintenance program to ensure valves operate correctly and don’t seize.
31. What is the primary cause of cavitation in pumps?
Insufficient suction head causing vapor bubbles to form and collapse.
32. What does AWWA stand for?
American Water Works Association.
33. What is the recommended flushing velocity for cleaning water mains?
At least 2.5 ft/s.
34. What does a flow meter measure?
Volume of water passing through a pipe over time.
35. What is the primary purpose of looping distribution mains?
To maintain water circulation, pressure, and chlorine residual.
36. What is the definition of MCL?
Maximum Contaminant Level allowed in drinking water.
37. What is the minimum recommended distance between a water main and sanitary sewer?
3 m horizontally, with water above sewer (Ontario guidelines).
38. What is the function of a blowoff valve?
To flush dead-end mains and remove stagnant water.
39. What is the purpose of cathodic protection?
To prevent corrosion of metal water mains and tanks.
40. What is the minimum depth of cover for water mains in cold climates?
Below frost depth, typically 1.5–2.5 m (5–8 ft).
41. What is a tracer wire used for?
To locate non-metallic pipes such as PVC or HDPE.
42. What is the typical life expectancy of a ductile iron water main?
50–100 years depending on soil and corrosion conditions.
43. What is the purpose of a system map or GIS?
To locate mains, valves, hydrants, and aid in system management.
44. What is the recommended minimum pressure during fire flow conditions?
20 psi.
45. What is the most important parameter to monitor after changing chlorine dose?
Chlorine residual in the distribution system.
46. What is the difference between free and combined chlorine?
Free chlorine = available disinfectant.
Combined chlorine = chlorine bound with ammonia (chloramines).
47. What is the purpose of swabbing a water main?
To clean and remove biofilm and sediment buildup.
48. What is the recommended minimum chlorine contact time (CT) for effective disinfection?
Varies with conditions; Ontario standards require CT ≥ 15 minutes at peak flow.
49. What is the purpose of an interconnection between two systems?
To provide backup supply and redundancy during emergencies.
50. What is the first action an operator should take when receiving a water quality complaint?
Gather details from the customer, then investigate in the field (check pressure, chlorine residual, and flushing if needed).
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