Hetch Hetchy water goes through ultraviolet rinse

For the first time ever, San Francisco’s water is being bathed in ultraviolet waves before flowing to faucets.

The San Francisco Public Utility Commission’s new water treatment facility — which the agency boasts is the largest UV treatment plant in California and third largest in North America — has recently begun shining massive light bulbs though pipes filled with pristine Hetch Hetchy water to decontaminate it.

The $114 million project was made necessary by new U.S. Environmental Protection Agency regulations that require all nonfiltered water sources to go through two separate forms of decontamination.

San Francisco’s water source taps Sierra Nevada snowmelt from the dammed Hetch Hetchy Valley, and is already considered one of the purest sources of water in the world, so its managers were loathe to begin filtering it, said Julie Labonte, the SFPUC’s water system improvement director.

Instead, they decided to replace their 70-year-old treatment facility with one that supplements their conventional chemical treatment of the water with a UV system. The relatively new technology works by soaking the water with UV rays — lethal to both giardia and cryptosporidium, parasites that are resistant to treatment by simple chloramines, which kill almost everything else.

Cryptosporidium can be especially difficult to eradicate, and that parasite can be particularly dangerous for people with suppressed immune systems, Labonte said.

“So in a population like San Francisco it’s critical to treat for that,” she said.

Construction began on the new facility in 2009 and it was completed last month. It has been functioning on a trial basis and will be officially dedicated today. The deadline for completing the two-treatment system is April.


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