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Earthwatch
Achieving Water Security Now
by Jim Bell
As the moon exerts its gravitational attraction upon the Earth, the tides respond by rhythmically rising and falling. If you stand along the ocean shore, the water seems vast and endless, stretching beyond limits. Water, water everywhere. But is there enough water on this planet to provide all that we want to drink, shower in, swim in, and grow food with?
Many experts are projecting doom and gloom scenarios of decreasing water supplies and increasing cost. However, the San Diego/Tijuana Region can easily become water self-sufficient and even a net water exporter.
Sound incredible? 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 of the freshwater it currently uses by installing photovoltaic (PV) panels over a mere 4.3 percent of its roofs and parking lots.
To be clear, the above statement assumes a yearly average of five hours of sunlight per day, 1,000 square feet of roof and parking lot per capita, an average potable water consumption level of 180 gallons per capita per day, and a 2015 regional population of six million people.
With these conditions in place, 70 gallons of freshwater can be extracted from seawater through reverse osmosis (RO) per kWh of electricity consumed. This assumes that PV panels are 15 percent efficient at converting sunlight into electricity (commercially available panels are already pushing efficiencies of 20 percent or better). The electricity produced by this system would power large scale 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 controversial issue of sucking marine life into RO systems can be solved if the seawater to be processed into freshwater is extracted from wells close to the ocean above high tide instead of through direct ocean extraction. Since seawater coming into such wells would be sand filtered, marine organisms will be eliminated from the process.
Similarly, since “wastewater” from the RO process will be twice as salty as seawater, it will have to be diluted with seawater also extracted from the near ocean wells until the water to be returned to the ocean is no more than 20 percent saltier than seawater. Once diluted, its release into the ocean would be defused as an additional precaution against negative ecological consequences. Other sand filtering technologies have also been proposed.
Mining RO wastewater 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 magnitude of the “worst case scenario” RO system discussed above could be cut in half if recycled sewage water were filtered, disinfected, and used for irrigation. Using greywater at home would also be a plus for efficient water use. This is because half of the potable water currently used in the region is used for irrigating landscaping and crops. Water efficiency improvements could reduce the role of renewable-energy-powered RO as well.
By combining water recycling and efficient water use with better rainwater runoff collection and storage systems, the region would only need to install 15 percent efficient PV panels on two percent 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.
All of this can be funded through a water purchase agreement model that will pay for itself by redirecting the dollars we now export to pay for imported water into hiring local businesses and workers to make our region renewable water self-sufficient, with renewable energy powered RO being our backup for water if all else fails. The solution is available now. It simply requires a commitment to sustainability that can only come through a transition from water exploitation to water self-sufficiency.
Jim Bell is an internationally recognized expert on life-support-sustaining development with over 40 years experience in the design and construction industry. 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, and the Ocean Beach People’s Organic Food Co-op’s green store. For free online books, videos, and commentaries on how to use free-market investment strategies to create life-support sustaining economies and ways of life on our planet, go to www.jimbell.com.