volume 2 - resource management Strategies
Cross-connections and backflow in distribution systems represent a significant public health risk.
Water quality problems can be related to infrastructure problems and aging of distribution systems may increase risks of infrastructure problems.
Distribution systems are highly complex and there is a significant need for additional information and analysis on the nature and magnitude of risk associated with them.”
The maintenance of water quality within the distribution system has received considerable attention in recent years, especially as systems have modified methods of treatment. Changes to the methods and levels of disinfectants can create the potential for reduced control of microbial contaminants that may be present in the distribution system.
An example of the serious consequences of potential degradation in the distribution system occurred during March of 2008 in the town of Alamosa, Colorado. This town of about 8,500 residents experienced an extensive Salmonella outbreak that sickened at least 389 people; 16 were hospitalized. The contamination was attributed to the town’s drinking water. In this case, the water supply wells were found to be clean, and the source of the Salmonella within the distribution system has yet to be identified, but were noted to be present in indigenous wildlife.
Water utilities are also constantly making improvements to their distribution systems, including increasing the reliability of their water supplies. One example is the installation of emergency water interties between neighboring water utilities. These provide a backup source (the neighboring water system) in the case of an outage due either to some unforeseen emergency or potential disaster, and also allow a water utility to shut down a part of its system to do necessary maintenance without interrupting service to customers.
For example, there is an emergency intertie between the East Bay Municipal Utility District, City of Hayward, and the San Francisco Public Utilities Commission (SFPUC) to supply treated water between the three water systems and is intended to be used during planned outages for needed maintenance and to avoid service interruptions. EBMUD has two small interties, each able to carry 4 million gallons per day, with the City of Hayward, which adjoins its service area. SFPUC, which is the agency in charge of the Hetch Hetchy water used by many Bay Area water districts and residents, constructed an intertie with the Santa Clara Valley Water Agency and has been considering another. These interties may also play a role in the security of the water distribution system by creating a backup source should a terrorist action disrupt the source of supply from a water provider.
In other cases, interties can provide untreated water between utilities to provide untreated source water in an emergency. For example, Contra Costa Water District (CCWD), whose service area is crossed by EBMUD Mokelumne pipeline, has an
caLifoRnia WateR PLan | update 2009