Californians have been stepping up to the challenge of meeting Governor Brown's water conservation goals; the numbers for May showed a 29 percent reduction in water use, a laudable achievement showing concerted effort by water districts and residents throughout the state. The good news: we're half way there. But the other half of the empty glass is still there, with a looming February 2016 goal of an additional 611,000-acre feet savings to go, statewide. We've already ripped out lawns and amped up recycling and are well on our way to more rain and stormwater capture. What more can we do?
There is an untapped conservation resource right at the end of the tap. Every building could re-use the water from everywhere but the kitchen sink and the toilet. Called "greywater," this lightly used and mostly soapy water from showers, bathtubs, handwashing sinks, and laundry machines can be used for landscape irrigation at a minimum. A "showers to flowers" (also known as "laundry to landscape") system could meet about 25 percent of outdoor irrigation demand in urban areas depending on the plant palettes used. In the City of Los Angeles, about 140,000 acre-feet a year of drinking water could be saved if greywater reuse were maximized in residential (single-family and multi-family).
Recognizing this, in July of this year the California Water Commission (of which I am a member) adopted the state Model Water Use Efficient Landscape Ordinance that sets the bar for all California municipalities and encourages greywater use for landscaping.
But even greater savings could be achieved if new office buildings, commercial buildings, and hotels, were dual plumbed to use treated greywater for toilet flushing, irrigation, and cooling tower makeup water supply. The 2013 California Green Building Standard Code (CALGreen) already includes language to encourage greywater reuse for indoor purposes such as for water closets, urinals and other allowed uses. It makes sense. Large buildings with drought-tolerant landscapes have low irrigation water demand. Why not take the surplus and use it for something else? Also, think about it: why should we ever flush drinking water down the toilet?
If office buildings, hotels, restaurants, and schools were to use this option, they could reuse - and therefore conserve -- anywhere from 15 to 30 percent of their total water use. Even if a really wet winter slakes our thirsty soils for a season, it will all amount to a proverbial drop in the long-term bucket that is our new normal of water. Why waste any of it when we have the technology to treat it in a way that maximizes every drop safely? There are existing turnkey systems which residents can use, and commercial building owners can custom design a re-use system of their own.
Cities have the power (and some already use it) to create regulations to allow greywater reuse beyond subsurface irrigation. In 2011, AB849 amended the Health and Safety Code and the Water Code to give local authorities the ability to develop their own greywater building standards.
San Francisco has taken a number of steps in this water-wise direction and added the Non-potable Water Ordinance into their Health Code. This ordinance allows for collection, treatment, and use of non-potable water, including greywater, in commercial, mixed-used, and multi-family residential developments. The ordinance has led to the creation of a guideline that specifies requirements for allowable onsite water reuse activities. Also, San Francisco has provided financial incentives to encourage onsite water reclamation. The San Francisco Public Utilities Commission has featured projects that have been approved under this ordinance in their Non-potable Project Profiles. San Francisco Public Safety Building, the Transbay Transit Center, and 181 Fremont Mixed-use Tower are buildings that will collect, treat, and use greywater for toilet flushing and cooling tower makeup water, in addition to irrigation. San Francisco is leading the way in fostering more onsite water reuse activities. This can replicated throughout California.
Greywater can help us become more drought prepared and resilient, especially in the more arid south. What else? On the economic front, greywater-friendly regulations could lead to more jobs, and opportunities for technology advancement, which usually leads to lower treatment costs. Given these benefits, and our need to achieve greater long-term water sustainability, greywater could be a way to fill the rest of the water conservation glass.
This post was co-authored with Zita L.T. Yu, Ph.D., a greywater recycling specialist. Zita is a Water Resources Engineer at Geosyntec Consultants. She also serves on the Steering Committee of Southern California Water Dialogue.