GrokSurf's San Diego

Local observations on water, environment, technology, law & politics

San Diego power outage: why were some areas under a “boil water” advisory?

Posted by George J Janczyn on September 12, 2011

A few areas in San Diego County were under a “boil water” advisory during/after the power outage.

Some people have been asking: “I still don’t understand the “boil water” order; how/why does the possible contamination come about?”

There were a few pressure zones where pumps lost power. I’m not sure if they lacked backup power or if there was a malfunction in the backup. I thought all had backup, but then I thought all wastewater pumps had backup too! Some homes were reporting no water at all coming from faucets.

Anyway, when water pressure is lost in the delivery system, the potential exists for water to siphon back into the system from landscape irrigation systems, garden hoses, in-home plumbing, and probably other places. Landscape irrigation systems are supposed to have anti-siphon devices installed, but many do not or may not be working, and in any case, they aren’t the only sources of potential contamination.

Whenever such a breach occurs, the assumption is contamination until they restore pressure, flush the system, and run water quality tests.

As things turned out this time, tests revealed no problems.


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