Water Distribution Systems and Storage
What the candidate must know
Distribution systems deliver treated water while maintaining pressure and residual disinfectant. Know the components: mains, service lines, meters, valves, hydrants, storage tanks, and booster pumps. Understand pressure requirements, storage purposes (fire flow, demand equalization, emergency reserve), and the causes of distribution water quality problems.
Concepts to master
- Minimum and normal operating pressure expectations and the role of pressure-reducing valves.
- Storage tank operation: fill/draw cycles, turnover, and the risk of stagnation and nitrification in warm water.
- Disinfectant residual maintenance and the difference between free chlorine and chloramines.
- Cross-connection control and backflow prevention (air gaps, RPZ devices).
- Main flushing, valve exercising, and hydrant maintenance programs.
- Water loss and metering.
Traps in questions
A frequent trap is assuming higher pressure is always better - excessive pressure increases leak and break rates. Another is confusing a backflow preventer type with its application, or forgetting that dead-end mains and oversized tanks promote stagnation.
Worked example / rule of thumb
Rule of thumb: maintain adequate turnover in storage; if a tank's water age climbs, residual drops and nitrification risk rises. For backflow, an air gap provides the highest protection; an RPZ is used where backpressure or backsiphonage hazards exist.