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November 2, 2015

San Diego turns Pacific Ocean into safe drinking water


Despite criticism from environmental groups, San Diego County will open the largest seawater desalination plant in the western hemisphere this year in an attempt to combat California’s four-year drought.

The plant, which takes salty ocean water and turns it into fresh drinking water in a process known as desalination or “desal,” will be able to pump 54 million gallons of water a day into homes. That’s enough water to fill an Olympic-sized pool every 18 minutes, according to Bob Yamada with the San Diego Water Authority.

The plant draws in saltwater from the Pacific Ocean, filtering out any marine life. Next, sand and chemical filters clean the water. The third step is called “reverse osmosis,” which uses thousands of tubes to remove larger salt particles. The captured salt is diluted and sent back into the ocean. Finally, high-powered pumps send the water through pipes and into the aqueduct that serves around 300,000 San Diego residents.

Although the project has received overwhelming support from local residents, environmentalists worry the desal process will generate greenhouse gases that could contribute to more frequent droughts, according to Matt O’Malley with the California Coastkeeper Alliance. The group has filed several failed lawsuits to delay construction of the plant.

The plant will burn through 840 megawatts of power per day — about the same amount of electricity used to power nearly 30,000 homes. Other potential hazards include questions of long term effects from dumping large levels of concentrated salt back into the ocean.

Peter MacLaggan, senior vice president of Poseidon Water, said the company is closely monitoring salinity levels around the plant. He added that even though California is expected to get more rain due to El Niño, the technology is needed.

“It can rain buckets all winter long, and that will be a great thing, but it’s not going to eliminate the need for this facility,” MacLaggan said.

desalination — a process that removes the excess salt and other minerals from water in order to obtain fresh water suitable for consumption or irrigation
reverse osmosis — a method of water purification using a semipermeable membrane to remove larger particles from drinking water
aqueduct — an artificial channel for conveying water
El Niño — a warming of the surface water of the eastern and central Pacific Ocean, occurring every four to 12 years and causing unusual global weather patterns
Warm up questions
  1. Where does our drinking water come from?
  2. What do you know about the water crisis in California?
  3. What can be done to help alleviate the effects of a drought?
  4. What should individuals do during a drought?
Critical thinking questions
  1. Do you think desal is the best way of addressing the drought in California?
  2. What kinds of long term effects do you think removing water and pumping salt back into the ocean could have on the environment?
  3. Why are cities in California planning desal plants even though scientists predict considerable rain this winter?
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