March 19

Toilet To Tap


The following was saved from the old website, just in case anyone was looking for it (with the help of

Toilet to Tap: Once Again

Indirect potable reuse is assuming a life of its own in the American West. Are we heading in the right direction?

By Penelope B. Grenoble

Toilet to Tap—with all that’s gone on in the West in the last half-dozen years, from drought to reallocation of Colorado River water, and restrictions coming out of California’s Sacramento Delta, the once-maligned, supply-side strategy seems to be an idea whose time has finally come.

Supposedly attributed to a clever copy editor at the Los Angeles Daily News, “Toilet to Tap” brought down a 33,000-acre-foot groundwater recharge project slated for Los Angeles’ San Fernando Valley, as well as projects in San Diego and Dublin, CA. But the continuing issue for water professionals is that the negative and potentially divisive phase suggests that developing new sources of potable reuse is a simple and capacious undertaking.

In traditional water systems, raw water is diverted from its source in a lake, stream, or aquifer; treated; and distributed, with little more to do. Wastewater is subsequently collected, treated, and discharged to a receiving body. The fact that, in many places in the US, this results in unplanned potable reuse (as the Southern Nevada Water Authority puts it, “borrowing water”) does not in any way diminish the well-developed planned reuse projects emerging in this country.

Planned potable reuse in the US is largely indirect, wherein treated effluent is subject to multiple contaminant-removing barriers, from extensive chemical and physical treatment to dilution and natural cleansing in soil or a body of water. In a 1998 report, the Water Science and Technology Board of the National Research Council’s Commission on Geosciences, Environment, and Resources concluded that, while analytical and toxicological testing, as well as epidemiological studies, have identified no significant health risks in communities using reclaimed water, indirect potable reuse projects should exceed the requirements for conventional water treatment and should employ strong chemical disinfection processes in addition to physical treatment systems. Also, barriers for microbiological contaminants should be more robust than in conventional water treatment.

So, what does it look like out there? Is jumping on the reverse osmosis (RO) bandwagon the way to go? Or is nature perhaps a resource we’ve bypassed in our regulatory zeal? Is it more effective to pull out all the stops before the effluent goes into the ground or treat it as it’s drawn out?

Southern California is served by a complicated mix of city and county utilities, which are in turn regulated by a Byzantine web of agencies, so it might be surprising to learn that Los Angeles has been practicing potable reuse since the 1960s. While Orange County has made a splash with its huge 70-million-gallon-per-day Groundwater Replenishment Project, the Water Replenishment District of Southern California (WRD) has been quietly recharging groundwater with tertiary-treated wastewater, in part with effluent supplied by West Basin Municipal Water District. The WRD’s original rationale was similar to Orange County’s emphasis in its groundbreaking public outreach campaign—protection of natural groundwater by maintaining the barrier that keeps saltwater from contaminating the region’s aquifers. And if some of this water also makes it into raw supplies used for drinking water, well, so be it.

Over the years, WRD has used a mix of treated effluent, stormwater running off the San Gabriel Mountains, and potable water supplied by the Metropolitan Water District of Southern California to recharge the Central and West Basin aquifers, two of the most heavily used groundwater basins in California, serving four million Los Angeles County residents.

Recurrent drought convinced various powers-that-be that neither nature nor the Metropolitan Water District was reliable enough to keep the aquifers and the sea barriers supplied, and, in 1995, West Basin christened its own advanced water treatment plant. Today, it produces what it describes as five distinctive grades of “designer” recycled water: tertiary, nitrified tertiary (with the ammonia removed for use in industrial cooling towers), softened RO (secondary treated wastewater pretreated by either lime clarification or ultrafiltration, then followed by RO and disinfection—the water that’s now used for groundwater recharge), pure RO (secondary treated wastewater that had undergone microfiltration, RO, and disinfection for low-pressure boiler feed water), and ultrapure RO (microfiltration,  RO, disinfection, and second-pass RO for high-pressure boiler feed).

Both West Basin and WRD have committed to increasing use of recycled water as a means of diversifying their water supply portfolios. To this, West Basin has added more efficient water conservation and ocean desal. The target shared by both agencies, to increase the amount of recycled water used in Los Angeles’ seawater barriers from 75% to 100%, is also a goal in Orange County.


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