SoCal desalination plant to combat drought

CARLSBAD, Calif. (KTVU) - California's four year long drought has sparked talk of opening desalination plants to make fresh water from the sea.

A state-of-the-art desalination plant is set to open in San Diego County by the end of the year. But the technology has been around for decades.

The USS Midway is a historic aircraft carrier that's been converted into a floating museum in San Diego.

KTVU went through the maze of passageways and five decks down to the engineering spaces where thousands of gallons of sea water was pumped to on board distilling plants.

Emory Bishop, a former Midway engineer, gave KTVU a tour.

"Seventy thousand gallons per day each day and we've got four of them on the Midway," said Bishop.

The Midway was commissioned back in 1945 just days after the end of World War II. At the time, it was the largest ship in the world and served the Navy for 47 years.

Part of that time it was home ported at Alameda.

4,500 men lived aboard her while the ship patrolled the globe, each one needing fresh water.

"It's a precious commodity," said Bishop.

The process of making fresh water is relatively simple. Sea water is heated in a vacuum to create steam. It's a process the Navy still uses today.

"The water flashes to steam because when it comes in its at about 145 degrees and the flash point at 25 inches of mercury vacuum is around 130 degrees so it flashes to steam," Bishop said.

It's a five step process with color coded pipes. Green pipes marks sea water, blue is fresh water and white is steam. Bishop says an aircraft carrier needs a lot of steam.

"We use the steam to run the turbines and the pumps and the steam that's exhaust from that is still hot, it's still got a lot of energy in it we use that and we call it waste heat. We use that waste heat to make water," said Bishop.

280,000 gallons of fresh water and steam were created here every day at sea, but there's hardly a drop to waste.

Much of the steam is used to propel the catapult which launches the aircraft, in the Midway's case it was often an F-4 Phantom, off the flight deck and into the sky.

Each catapult launch required 70 to 80 gallons of water.

"You're doing a lot of sorties, a hundred sorties a day, you're looking at 800, a thousand gallons of water just to run the catapult," said Bishop.

The steam was also used for cooking on the mess decks. Sailors got hot showers but were required to conserve water.

"We called them Navy showers," Bishop told KTVU. "You rinse off, get wet, soap up, then turn the water back on and rinse off. You can take a shower and use less than two gallons of water."

If this system works so well, why isn't it used to supply drinking water on shore?

"There's a lot of maintenance on this type of plant. You know we got lots of sailors to do that. You talk in the civilian world the maintenance is lots of dollars," said Bishop.

And a lot of power. In the end it costs about twice as much for desal water as it does from existing reservoirs.

"It's not super efficient," said Bishop. "About 15 to 18 percent is all."

Modern desal plants don't use steam. Instead high pressure filters sea water through membranes into fresh water. But it's still expensive, more so than conservation or recycling waste water.

Residents in San Diego County will soon learn if the high cost is worth it when their desal plant opens later this month.