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I’ve gotten a couple of questions from readers who are worried that no matter how well a sewage recycling system can be designed, the city of San Diego will find a way to screw it up and not operate it properly.

Such a system is designed with fail safes so that if something goes wrong, it can automatically shut itself down.

Reader RF writes:

In our current city water system, someone tests water samples regularly; however, due to lab delays, no one knows the results of tests for 3(?) days. Thus, today we can say confidently that the water we drank three days ago was good, but we won’t know until next week about today’s water. If we implement “toilet-to-tap”, will we continue to have a time delay of three days on tests?

We don’t have that time delay today for our drinking water. The county’s now-defunct beach water quality monitoring program took several days to produce results about bacteria levels in the ocean — the result of the available testing. But the city’s water treatment plants, which disinfect drinking water, get some results instantaneously.

Dan Chapin, the city of San Diego’s water production superintendent, said several indicators of water quality are constantly monitored — such as the turbidity (the water’s clearness) and levels of disinfectants. If any are out of line, treatment plants can be shut down.

The Orange County Water District, which started recycling sewage in January, has a system that’s constantly monitored electronically, said Mike Wehner, the district’s assistant general manager.

“If something were to happen in the treatment plant, we get an almost immediate response in seconds,” Wehner said, noting that certain changes in the system prompt it to automatically shut down — like the summer’s earthquake.

Since the Orange County plant began operating, it has not had any shutdowns because of water quality problems or treatment problems, Wehner said. It has had no water quality lapses, he said.

The system has shut down a few times, but only when it was being modified or when software or hardware updates have been installed, Wehner said.

ROB DAVIS

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