recycling water to save money

San Diego is in a tough spot when it comes to water.  It’s at the far end of the pipeline when it comes to imported supplies from the Colorado River and the California aqueduct, and the Metropolitan Water District (MWD) subsequently charges the San Diego County Water Authority extra for pumping over the extra distance.  It gets less annual rainfall than the LA Basin (10.3 inches in San Diego, 15.1 inches in LA) and has no significant natural rivers (the San Diego River has a flow an order of magnitude lower than the two biggest rivers in the LA Basin, the Los Angeles River and the San Gabriel River), so in some ways it needs imported water even more than Los Angeles.  On top of that, its main wastewater treatment plant, Point Loma, is likely to have its waiver from Secondary Treatment requirements of the Clean Water Act not renewed.  The cost of the required Point Loma upgrades for a 2015 permit could be $1.2 billion.

So a new study for the City of San Diego proposes a way to kill two birds with one stone: recycle treated wastewater into the drinking water supply.  The wastewater discharged to the ocean would decrease, as would the delivery of imported water.  The idea seems to be amenable to the public – a 2011 survey found that two-thirds of the respondents favored adding highly treated recycled water to the drinking water system – and depending on rate increases from MWD, the cost could eventually be lower than imported water.

Water reuse also requires infrastructure, with costs of $2.7 – $3.4 billion over 50 years projected by the report, but the cost savings in required Point Loma upgrades (cost scales with the volumetric flow rate of water treated) could result in a very favorable cost-benefit ratio.  If San Diego pursues this strategy, it could be on the cutting edge of water management in the US.


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