Thanks to our readers for their questions about my story today on the science of recycling sewage. I’m going to pick off a couple. Here’s the first.

Reader KB writes:

I had one question about the penultimate paragraph when you say: “Water agencies will someday feel comfortable putting purified sewage directly into drinking-water pipes.” So, they aren’t right now?

Water agencies feel comfortable, but the state’s Department of Health doesn’t. In Orange County, the state requires the purified sewage to sit underground for at least six months. That’s the same length of time the state requires non-purified sewage to sit underground before being going to a water treatment plant and then drinking water pipes. The state doesn’t differentiate between purified and non-purified sewage — it all has to stay underground six months.

We’re talking about two different types of water here: purified sewage and treated sewage.

Currently, water agencies can get regulatory permission to let treated sewage soak into groundwater aquifers. Once underground, it has to stay for six months before people can drink it.

The Orange County sewage recycling project takes that treated sewage and puts it through an additional three-step purification process. It goes through filters, reverse osmosis membranes and then gets zapped with hydrogen peroxide and ultraviolet light. Even though the water comes out clean, the state still requires it to stay underground for six months.

So regardless of whether it’s purified sewage — which is basically distilled water — or just treated sewage, it has to stay underground.

“From our perspective, it’s a redundancy,” said Mike Wehner, the Orange County Water District’s assistant general manager. “Our confidence in the system is quite high.”

The water would be pure enough to put in pipes, Wehner said, and some members of the district are pushing for that to happen. It hasn’t yet, though. Wehner said, “It’s mostly an issue of public uncertainty.”

More answers to come.

ROB DAVIS

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