Distribution System Contamination Prevention: Mechanisms and Solutions

Mechanisms

Hypothesized Necessary Conditions

Proposed Best Practices

Household Storage: A household’s water storage supply can be contaminated if hands, debris, animals or improperly washed utensils are dipped into the storage tank

• Lack of faucets
• Open tank

• Sealed tank with   adequate household plumbing

Cross Contamination: Negative pressure transients in pipes or privately attached pumps can suck contaminated water from household storage systems or other connections into the distribution system.

• Intermittent supply
• Submerged outlets
• Connection to contaminated source (ground water, contaminated storage water…)
• Negative internal pipeline pressure

• Float valve in water tanks
• Backflow prevention device

• Prohibition against private pumps
• Proper operator training

Pipeline intrusion:  May occur when there is a leak or other type of pathway and the internal pressure of the pipeline drops below external hydrostatic pressure, sucking contaminants into the system.

• Booster pumps attached to system
• Large pressure transients (Pump shutdown, sudden valve closure…)
• High water table
• Contaminated soil profile

• Elevated storage tanks

• Prohibition against private pumps
• Proper operator training
• First flush system in household distribution tanks
• Check valves at household outlets

Bacterial Growth inside the pipeline: Potentially may occur if there was a constant, stagnant volume of water kept inside a pipeline for extended periods of time  (unlikely)

• Constant water level
• Stagnant water

• Regularly use distribution system
• Usually, a little excess chlorine is dosed to prevent growth in the distribution lines