50 shades of graywater: recycling graywater worth the effort, says new ucla study

50 Shades of Graywater: Recycling Graywater Worth the Effort, Says New UCLA Study

By Tetra Balestri, Student Contributor

Most Los Angeles households have bins and services for recycling their paper, plastic and even their yard waste.

But in this time of extreme drought in California — why aren’t we talking more about recycling water? Not only would it save water, but money too, according to a new study by UCLA researchers, including faculty affiliated with the Institute of the Environment and Sustainability.

The study finds that treating and recycling Los Angeles’ excess “graywater” — the gently soiled water drained from showers, bathrooms and washing machines — could not only save homeowners money on their water bills, but also reduce demands for drinking water and even energy. “About half of your water bill is your wastewater bill,” says J.R. DeShazo, director of UCLA’s Luskin Center and Professor of Public Policy and Urban Planning and a study author.

Published in the Journal of the American Water Works Association, the study was conducted by engineer Zita L.T. Yu as part of her doctoral research on graywater at UCLA, in collaboration with UCLA faculty members DeShazo, Michael Stenstrom and Yoram Cohen.

Going Gray = Going Green

At present, only about 1% of Los Angeles’ water supply comes from conserved or recycled water. The majority of the city’s water is purchased from the Metropolitan Water District or sourced from the Los Angeles aqueduct, and a smaller amount drawn from groundwater.

But data collected from the city’s water supply in 2013 indicates that 25% of the water used on a daily basis — in washing machines, showers, bathtubs and handwashing sinks — has the potential to be used as recycled graywater for three non-potable purposes: irrigation, toilet flushing, and laundry. Currently, L.A. uses drinking water for these activities.

The study found that, if a single-family household was to recycle and treat its graywater, it could displace as much as half of the water it uses to irrigate its grounds and, consequently, reduce its daily potable water use by about 27% per day.

On a larger scale, the study revealed that recycling just 10% of Los Angeles’ available graywater could reduce potable water demand by 2% — which, when multiplied by the city’s total water amount, is significant.

What It Would Take for Los Angeles to Tap into Graywater

California law allows residential homes to use recycled graywater only if graywater is treated. But paying for treatment is still a financial hurdle for most homeowners. It requires purchasing an on-site treatment system; potentially retrofitting houses with the correct and necessary plumbing; and finally, keeping up with maintenance costs.

The study compared two types of filtration systems that are available for single-family homes to install on their property: wetland treatment systems and commercial systems.

  • Purchasing a commercial system could cost about $6,000 to $13,000 depending on the manufacturer. These systems vary in design but are often installed underground, like a septic tank. Graywater is piped into the system for treatment, then dispersed through a plumbing system to water the lawn, fill up the washing machine or sent to a reserve tank for later use.
  • The wetland system is the more economical option, costing a household an initial $1,500 to $2,500. This treatment system resembles and functions like a wetland. One design, for example, uses aquatic plants rooted in sand to filter water. Graywater is passed through their roots to undergo processes such as sedimentation, filtration and biodegradation, before coming out of a hose on the other end. Graywater treated through wetland systems is generally limited to irrigation use.

Although these systems may seem expensive to the average homeowner, the new research shows that initial investment of an onsite, economical system, such as the wetland treatment system, will save single-family homeowners money in the long run.

Considering a family whose water use exceeds 42 gallons per day, maintaining a treatment system would cost less than the water and sewage charges accrued.

In addition to saving water, these systems could save energy, according to the study. The energy required to recycle graywater using the wetland system is lower than the energy required to use water purchased from the Metropolitan Water District.

Despite these benefits, in order for graywater recycling to effectively take hold, the city would have to provide incentives for homeowners.

As city policies currently stand, there is no financial system in place that credits homeowners for reducing or treating their wastewater.

“There is a huge physical and technical opportunity here,” says DeShazo. “We just don’t have any of the incentive systems in place. Either in the construction side when the buildings are built, or on the wastewater or financial size to credit them.”

Indeed, the advantages of graywater recycling outweigh other recycling water methods such as centralized stormwater capture because graywater recycling is available with more frequency year round.

The Future of Graywater

Although state-initiated financial incentives are not in place, many contractors are adopting graywater plumbing systems when building new multi-family homes, says DeShazo.

“In terms of green building codes and incorporating them into new construction, this is something that is actively being considered,” he adds. “The most progressive developments like playa vista and others are starting to require certain minimal amounts of on-site irrigation from recycling.”

If incentives were available to encourage the purchase of treatment systems, the transition to graywater recycling could be easier. The study suggests providing rebates or low-interest financing to incentivize homeowners and offset the investment of a treatment system. They recommend third-party ownership models to allow smaller homes to share the costs with bigger institutions.

“One of the future extensions of this work would look at developing systems in which a green space owner operator compensates the multi family housing owner for the supply of their recycled graywater.” says DeShazo. If multi-family homes were adjacent to a large park or green area such as a golf course, these third parties could benefit from the recycling. Additionally, this arrangement would solve one of the challenges of what to do with the water.

As the California drought persists, Los Angeles is still without the infrastructure for a distribution system that centralizes recycled water. In a city of over 350,000 single-family homes, recycling graywater could be an inevitable and necessary step in water conservation for Los Angeles.

“This is a technology and an opportunity that we can build and grow our way into,” says DeShazo.