Wastewater Recycling: Creating Water So Pure We Can Drink It

Written by  Hillary Shipps
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Wastewater recycling, reclaimed water, and Indirect Potable Reuse (or IPR) are all ways of treating wastewater and reusing it rather than treating it and dumping it into the ocean.

San Diego reuses wastewater for irrigation, in its purple pipe system.  Purple pipe is so-named because it requires two sets of plumbing, one for drinking water (potable use) and a second (purple) set for reclaimed water for irrigation.  It’s easy enough to install when constructing a new building, but otherwise it’s a major retrofit, and either way it’s not cheap.  But during a bad drought in 1989, purple pipe was touted as the only way we would


Photo Credit Lighthawk / Matthew Meier Photography

make it through with enough potable water for showers and drinking.  The City Council even passed an aggressive ordinance to force anyone who could reasonably use reclaimed water for irrigation or industrial uses to do so.  But the drought ended, and since then the ordinance has been largely forgotten and essentially unenforced.  In fact, according to a Sign On San Diego article, San Diego only uses 15 percent of its two reclaimed water plants’ capacity.


Now, the city is taking another look at wastewater recycling for drinking water.  (Check out how purple pipe and IPR compare – spoiler, IPR wins.)  Mayor Jerry Sanders supports a new demonstration project to test the safety of IPR for drinking water – a definite improvement on his previous stance of ceremonially vetoing the “toilet to tap” project.  The latest test builds on the successful use of wastewater recycling in:

  • Singapore, where they use reservoir augmentation, the very same process proposed for San Diego, and bottle and sell the stuff under the brand name NEWater

  • And closer to home, Orange County, where they use wastewater recycling for groundwater replenishment

The demonstration project will last a year and is required by the California Department of Public Health to prove the project adequately protects the public health.  Tours of the facility are open to the public so you can see the high level of treatment the water receives.

The Advanced Water Purification process, which consists of microfiltration, reverse osmosis, and treatment with hydrogen peroxide and ultraviolet light, actually removes more contaminants from the water supply than do the processes used to clean raw imported water.  IPR water has been found to contain lower levels of all but six of the 232 tested pollutants, and those six were all still below levels that cause health concerns (check out page 108 of this report for details). The tested pollutants include pharmaceuticals and endocrine disrupters, which are a common concern about IPR water.

In the words of Ronald Coss, the technical manager of the Water Reuse Study that made the above finding, “the human health risk from consuming [IPR water] directly is negligible, especially when compared to current drinking water standards and with other water supplies available to San Diego.  Augmenting San Diego’s raw water supply with [IPR water] would result in an improvement to water quality over current water supplies.” 

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