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Contamination of treated water in the distribution system has the potential to negate the improvements to water quality provided by an AguaClara plant. Intermittent distribution systems may create the conditions for the mechanisms which cause this contamination to occur. The most likely mechanisms of distribution system contamination are pipeline intrusion, cross contamination and inadequate household storage. Through proper operator training, effective regulation and installation of secure storage facilities and backflow prevention valves, these mechanisms can be prevented and safe water delivered to all AguaClara households. |
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Distribution System ContaminationContamination of treated water in the distribution system has the potential to negate the improvements to water quality provided by an AguaClara plant. Intermittent distribution systems may create the conditions for the mechanisms which cause this contamination to occur. The most likely mechanisms of distribution system contamination are pipeline intrusion, cross contamination and inadequate household storage. Through proper operator training, effective regulation and installation of secure storage facilities and backflow prevention valves, these mechanisms can be prevented and safe water delivered to all AguaClara households. 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 | | - 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
| - 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
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Distribution System Contamination
It is common for cities to have drinking water treatment plants and yet still have tap water that is considered unsafe or unreliable. This reduction in water quality is often attributed to contamination that occurs within municipal distribution systems. Over the course of the semester, our team will investigate potential mechanisms of distribution system contamination and develop best practices to avoid this contamination in the future. Potential factors that we will investigate include:
- Contaminant intrusion into pipelines: It has been proposed that one mechanism of distribution system contamination is for contaminants to ingress into pipes when the internal pressure of the pipeline drops below the external pressure of the surrounding area. Over the course of the semester we will conduct experiments to test whether this intrusion is indeed possible and if so whether it constitutes a real threat to drinking water distribution.
- Effect of Intermittent supply: Due to inadequate infrastructure or water supply, many cities and towns in developing countries are forced to ration water that is delivered to citizens by only supplying water at certain times of the day. The constant cycle of turning on and off the water supply may cause large pressure transients,waves of energy that cause temporary, localized periods of high and low pressure moving through a pipe system. These transients can damage pipe networks and even cause negative pressure within the system that could potentially result in contaminant intrusion.
- Cross Contamination: Backflow from residential storage tanks could result in contaminants moving from those tanks into a municipal distribution system. We will develop a list of best practices to prevent this type of contamination.
