Journal Publishes Luskin Center Study on Graywater Recycling in Los Angeles

Journal Publishes Luskin Center Study on Graywater Recycling in Los Angeles

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Thu, 09/24/2015 - 9:54am

A study on residential graywater recycling, funded in part by the UCLA Luskin Center for Innovation, was published this month in the Journal of the American Water Works Association. The authors, Zita L. T. Yu, J.R. DeShazo— director of the UCLA Luskin Center, Michael K. Stenstrom, and Yoram Cohen performed a cost-benefit analysis of onsite graywater recycling in single-family and multifamily residences. Because residential use accounts for ~65% of Los Angeles’s water consumption, the city has encouraged rainwater capture projects in residential homes as an alternative source for nonpotable supply. The authors explore the potential for graywater to serve as an alternate source.

The amount of graywater, generated by the use of hand-washing sinks, showers, bathtubs, and washing machines is equivalent to ~25% of LA’s water supply (based on 2013 estimates). Graywater recycling is thus an appealing alternate source of nonpotable water as population growth and arid climate conditions constrain LA’s water supply. Yu et al. evaluated the economic drivers that foster onsite graywater recycling in their study, “Cost-Benefit Analysis of Onsite Residential Graywater Recycling: A Case Study on the City of Los Angeles.”

Decentralized graywater recycling benefits water agencies by better stabilizing the water supply and reducing energy demand. According to the article, “the cost of graywater recycling of $0.50/m3 using a low-cost treatment system would make graywater recycling competitive against other nonpotable options, including centralized water recycling.” Due to high (and rising) Metropolitan Water District (MWD) water costs, graywater may become an even more competitive alternative water source for nonpotable use, as Los Angeles relies on MWD for 48% of its water.

The authors compared a low-cost, wetland treatment system with a high cost commercial treatment system in order to evaluate the achievable cost-savings provided by residential graywater treatment systems. Commercial treatment options may only be economically feasible for multi-family dwellings with high water consumption. For single-family residencies, a wetland treatment system was found to be cost effective based on the amount of nonpotable water generally consumed by these households.

The study conducted a cost-benefit analysis of graywater recycling for property owners and water agencies and identified key economic drivers for fostering graywater recycling. Installing treatment systems at new construction sites was found to be relatively inexpensive; however, retrofitting single or multi-family residences can be costly. Building codes impact the cost of recycling treatment systems. For instance, materials have a large impact on cost as plastic plumbing materials are much less expensive than metal, but are currently only allowed in Los Angeles for small buildings due to fire hazards.

Finally, because of the potential cost effectiveness, the researchers suggest three policy levers that could incentivize graywater recycling treatment system installation at residences:

  • Increased rebates for homeowners who decide to install graywater treatment systems. Currently, it is quite expensive to retrofit residences, and rebates historically have been insufficient to cover the upfront costs.
  • Low or zero-interest financing options.  In addition to rebates, financing options may make installation more feasible for residents.
  • Third-party ownership model. This model is widely used for onsite solar power generation financing in the residential sector. Not only would this model diminish upfront financial barriers for customers, it would also provide a simple means for ongoing maintenance (maintenance costs can be high for graywater recycling treatment systems but regular upkeep is critical for proper system functioning).

The importance of this issue for the city’s water supply is clear. The article estimates that while recycled water accounts for only ~1% of Los Angeles’s water supply today, there is opportunity for it to provide quite a bit more. For example, if 10% of the population participates, graywater recycling could reduce potable water demand by 2% and wastewater treatment load by 3%.

A study on residential graywater recycling, funded in part by the UCLA Luskin Center for Innovation, was published this month in the Journal of the American Water Works Association. The authors, Zita L. T. Yu, J.R. DeShazo— director of the UCLA Luskin Center, Michael K. Stenstrom, and Yoram Cohen performed a cost-benefit analysis of onsite graywater recycling in single-family and multifamily residences.