Water, water everywhere: How San Diego Can Become Water Self-Sufficient—And Even Be a Water Exporter
A Commentary By Jim Bell
May 10, 2009 (San Diego)--Many experts are projecting doom and gloom, scenarios of decreasing water supplies and increasing cost, yet the San Diego/Tijuana Region can easily become renewable water self-sufficient and even become a net water exporter. Yes, that’s right. We can have plenty of water for drinking, showering, growing food and even swimming—with liquid assets to spare.
Even if we assume the worst case scenario of zero precipitation and the complete cutoff of all imported water, the San Diego/Tijuana Region could completely replace all the freshwater it currently uses by installing PV panels over 4.3% of its roofs and parking lots. In 2015, 4.3% of our region’s roofs and parking lots will be about 9 sq. miles, or as shown in the graphic, 4.5 sq. miles on each side of the border.
The above statement is based on the following assumptions:
1. A yearly average of 5-hr. of sunlight per day,
2. 1,000 sq. feet of roof and parking lot per capita,
3. An average potable water consumption level of 180 gallons per capita per day,
4. A 2015 regional population of 6 million people,
5. That 70 gallons of freshwater can be extracted from seawater per kWh of electricity consumed through reverse osmosis (RO)
6. PV (photovoltaic panels) 15% efficient at converting sunlight into electricity, (Commercially available panels are already pushing efficiencies of 20% or better).
The electricity produced by this system would be used to power large scale reverse osmosis (RO) pumps to convert seawater into freshwater. The pumps push seawater through filters that let freshwater through while excluding salt, other minerals and contaminants in general.
The issue of sucking marine life into reverse osmosis (RO) system can be solved if seawater to be processed into freshwater is extracted from wells close to the ocean above high tide instead of direct ocean extraction. Since seawater coming into such wells would be sand filtered, marine organisms will be eliminated from the process.
Similarly, since “waste water” from the RO process will be twice as salty as seawater, it will have to be diluted by mixing it with seawater, also extracted from the near ocean wells, until the water to be returned to the ocean is no more than 20% saltier than seawater. Once diluted, its release into the ocean would be defused as an additional precaution against negative ecological consequences.
Mining RO waste water for salt and other minerals opens up other local business and employment opportunities for the region and could potentially eliminate the need to return RO wastewater to the ocean at all.
The size of the “worst case scenario” RO system discussed above could be cut in half, if recycled sewage water was filtered and disinfected, then used for irrigation. Using graywater at home would also be a plus for efficient water use. This is because half of the potable water currently used in our region is used for irrigating landscaping and crops.
Water-use efficiency improvements could reduce the role of renewable-energy-powered RO as well.
Combining water recycling and efficient water use with better rainwater runoff collection and storage systems, our region would only need to install 15% efficient PV panels on 2% of its roofs and parking lots to provide equal or superior water use services in the future, compared with what we have today. Plus, if we want more freshwater, we can cover more roofs and parking lots with PV panels to power expanded RO capacity and create all the freshwater we want.
Jim Bell is an ecological, designer, author and lecturer who is an nternationally recognized expert on life-support-sustaining development. His projects include the design and construction of the San Diego Center for Appropriate Technology and Ecoparque, a prototype wastewater recycling plant in Tijuana, Mexico that converts sewage into irrigation water and compost. He also worked as a consultant for the Otay Ranch Joint Planning Project and the East Lake Development Company. He has also served as the ecological designer for a life-support-friendly hotel for Terra Vista Management and for the Ocean Beach People's Food Cooperative's new "green" store. Jim has more than 40 years experience in the design and construction industry. As a lecturer, Jim speaks to many groups each year. His lecture credits include the AIA California State Conference, the Society for International Development's World Conference in Mexico City, and keynote addresses at the University of Oregon's first "Visions for a Sustainable Future" conference and the State of Oregon's Solar Energy Association Conference. Jim is often interviewed on television, radio, and by the written press and has been a guest on National Public Radio and the Art Bell Show. Jim has served on the Board of Directors of the San Diego Ecology Center, I Love a Clean San Diego, Environmental Health Coalition, and the California Association of Cooperatives. Currently, he serves as Director of the Ecological Life Systems Institute and the San Diego Center for Appropriate Technology. He's also a Board Member of Ocean Beach People's Food Coop and is a member of the San Diego Regional Apollo Alliance.
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seawater capture wells
With projected rising sea levels, the time to make these RO sand-filtered wells is now.