Hear the companion radio feature to this post on The California Report.

Ten million dogs can't be wrong.

For the record: the route isn’t nearly as direct as the popular canine version. I tasted this water in Orange County and it’s fine — actually, a little “tasteless” since all the minerals had been removed from it as well. The engineering folks in both Orange County and LA’s Department of Water and Power will tell you that this recycled water has a “distilled” quality to it.

With the future of Southern California’s water supply in some doubt, municipal water managers are moving again toward the ultimate recycling strategy, which lingers in the public’s mind with such appetizing monikers as “toilet to tap.” The region went through a political tempest a decade ago as it tried to bring the East Valley Water Recycling Project on line, a system that did not use the final “advanced” stage of water treatment (being used today in the OC and proposed for the new effort by LADWP). Mired in engineering concerns and a public relations mess, the project was scuttled by newly-elected LA mayor James Hahn. Today, the technology has improved and now, the process has a successful SoCal track record for “potable re-use.”

The process is lengthy but pretty easy to understand. Here are the details, courtesy of the City of Los Angeles Department of Water and Power and Orange County’s Groundwater Replenishing System:

• First, the wastewater goes through a preliminary stage where all the trash and grit is screened out. Then comes the primary stage where “solids” (I think you know what I’m talkin’ about) either settle to bottom or float to the top: those are removed.

• At the secondary stage, microbes are added: those wonderful little creatures that actually feed on the organic matter, nature’s original recyclers.

Kimberly Ayers

Wastewater enters the tertiary treatment process at the Tillman reclamation plant in Van Nuys.

• A sand filter stage starts the tertiary process, and removes finer particles. Then can come a chlorine disinfection after which — very important — the chlorine is then extracted.  What you’re left with is tertiary water, which meets state health department standards for purposes such as freeway landscaping, artificial snow — even safe enough for food crops. At this writing, “no health-related problems have been traced to any of the water recycling projects currently operating in California,” according to DWP.

This tertiary water keeps the Japanese Garden next to the L.A. Bureau of Sanitation’s Tillman plant in Van Nuys lush and green.  It also provides water to recharge the Los Angeles River.  Even the air conditioning at the Tillman facility is run on the plant’s tertiary water.

Kimberly Ayers

A single strand of microfiltration material

The final stage, the “advanced” process, sends the tertiary water through two final cleaning mechanisms. The first is reverse osmosis and/or microfiltration.  At this point, the water at the Orange County plant smelled pretty fresh, almost like a saltwater “seaside” smell. Microfiltration sends the already-treated water through hollow polypro fibers — think straws with tiny holes: bacteria and a good number of viruses are removed. Then comes reverse osmosis, in which the water is forced through thin filtering membranes at high pressure. This removes dissolved chemicals, pharmaceuticals and even more viruses.

The ultimate stages include zapping the water with untraviolet light and a peroxide disinfection. This stage removes dangerous trace organic compounds like N-nitrosodimethylamine (NDMA) and 1,4-dioxane. NDMA is a by-product of rocket fuel manufacturing, and 1,4 dioxane is a stabilizer used in industrial solvents. DWP has broken ground on a stand-alone UV filtering plant in Sylmar, north of downtown LA, as KPCC Radio reporter Molly Peterson reported earlier this year.  A side benefit of UV cleaning means that water engineers can use fewer chemicals to get the job done. UV is also an effective low-tech method: just ask the residents of Nairobi, Kenya’s Kibera district.

At the end of the advanced treatment phase, the water is pure enough to drink, and pure enough to be pumped back into your local water district’s reservoirs or groundwater basins, where it blends with the natural groundwater supply, waiting for its next journey to your tap.

Los Angeles Dept. of Water & Power

UPDATE: We’ve edited this post to correctly identify ownership of the Tillman treatment plant in Van Nuys.