Sewers to Sinks

A drought-stricken California county has found a new source of water: its toilets

By Jonathan Parkinson

In a separate, supermarket-sized building crowded with PVC tubes, water is forced at high pressure through thousands of plastic membranes in a process called reverse osmosis, which is also used by bottled water companies like Aquafina, Singapore’s indirect potable reuse program, and desalination plants. Contaminants like viruses, salts, chemicals, and trace pharmaceuticals are trapped by each membrane's microscopic pores as the water filters through. According to Shivaji Deshmukh, the program manager at OCWD, some things make it past reverse osmosis at appreciable levels: dissolved CO2, some 15-20 parts per million of dissolved salt (levels similar to those found in most brand-name bottled water), and a couple of other compounds. The potential problem is a carcinogen called NDMA, which can pass through reverse osmosis membranes at levels measured in parts per trillion. NDMA is believed to form as a result of chlorination of wastewater (ironically enough), and can come from certain industrial pollutants; even though it’s very difficult to filter or remove from water, NDMA rapidly disintegrates under strong ultraviolet light.

Hence the next step in OCWD’s process: OCWD adds hydrogen peroxide to the water and blasts it with UV rays to destroy organic compounds. The purified water is monitored extensively for quality, and finally pumped into the groundwater or piped to percolation ponds where it slowly trickles into the soil. Ultimately 20-to-25 percent of Orange County tap water is recycled, and the output is so pure “it actually improves groundwater quality,” says DePinto. 

This last step is actually unnecessary from a purity standpoint; it’s only undertaken, essentially, for PR reasons. People just seem to feel better about recycled wastewater coming from the ground like the rest of their water, rather than going directly into the water district’s pipes. 

Yet OCWD’s meticulous means of ensuring purity don’t satisfy everyone; critics contend that water from waste is too much to swallow. Though no one has been shown to have fallen ill in Orange County or in Singapore from drinking the recycled water, a lot of people and politicians just find the whole idea gross. (A San Diego Union-Tribune editorial about a similar proposal a few years ago began, “Your golden retriever may drink out of the toilet with no ill effects. But that doesn’t mean that humans should do the same.”) Most expert opposition has revolved around concern that there might be something dangerous that OCWD isn't testing for, or that the system could break down somehow, leading to a public health outbreak that's simply not worth the risk.

What some may not realize is that Westerners are already drinking sewage water: Las Vegas alone flushes 64 million gallons of treated sewage a day into the Colorado River, which feeds faucets throughout the Southwest; time, exposure to sunlight and banging against rocks does the OCWD’s job naturally. 

Still, like most other counties or districts considering sewage recycling, Orange County had to overcome widespread skepticism before they could convince the public. How would the system work? Was it safe?

“We spent seven years out there talking to anyone and everyone who would listen,” explains OCWD’s DePinto. “I think it was really important that we were being very transparent and open about what we were doing and how it works.” 

 1  |  2  |  3 

TrackBack URL for this entry:

Post a comment

« Plan a Green Holiday Party

Issue 25

Sign up for Plenty's Weekly Newsletter