Common Distribution System Deficiencies

This article was first published in the Winter 2012 issue of Spigot News, the Ohio EPA's drinking water program newsletter. Many thanks for allowing us to republish it! You may also be interested in the articles Common Source Water Deficiencies and Common Treatment Deficiencies. 

This article is a continuation of the series on common deficiencies, covering source, treatment and distribution deficiencies. This article covers different aspects of the distribution system, including cross-connection, backflow, depressurization events, water age and infrastructure deterioration. 

Cross-connection
A “cross-connection” occurs in areas of the plumbing system where non-potable water comes in contact with potable water. There are two types of cross-connections: direct and indirect cross-connections. 

Direct cross-connections – the potable system is permanently connected to a non-potable system (for example a submerged inlet pipe for a chemical feed system). 

Indirect cross-connections – there is a potential for a connection of the potable system to a non-potable system (for example, a garden hose connected to an outside hose bid without a vacuum breaker or a bidet with a douche sprayer or jet that fills the bowl below the rim). 

Establish cross-connection control ordinances for municipalities with diligent inspections of new and existing plumbing to prevent possible cross-connection issues. These issues may be identified during a sanitary survey or when real estate is bought and/or sold within the municipality. 

Backflow and Backsiphonage
A “backflow event” is when non-potable water is forced by pressure into the potable water supply due to a direct cross-connection. All distribution systems must maintain a minimum pressure of 20 psig and a 35 psig working pressure during all water demands including fires. Distribution systems that fall below these minimum pressures may experience a backflow event if an overpowering pressure differential is experienced by a competing cross-connection within the system. 

A “backsiphonage event” is when water flows backward in the water distribution system from a vessel or other contamination source because the distribution system has lost, created or reduced pressure. 

Backflow devices (backflow preventers, double check valves, testable reduced pressure zone device, etc.) are required on certain businesses that pose the most threat to a potable water system, but municipalities can require all businesses and homes within their jurisdictions to install and inspect backflow devices every 12 months. Another preventative measure may be to conduct a hydraulic assessment of the distribution system to identify those areas at most risk of a backflow event. Once identified, these areas can be targeted for improvement.