Weather Watch

Desalination could play a key role in the Central Coast drought

The state’s drought condition will continue to increase competition for water among agricultural, environmental, residential and industrial interests, and as the price of water increases, conservation will become progressively important.

However, conservation can only go so far. Current population growth predictions for California combined with expected longer dry spells and higher snowpack elevations in the Sierras due to climate change means new sources of fresh water will be needed.

The answer could come from the sea.

Consistently, the sun’s light combined with Earth’s winds evaporates enormous amounts of seawater into nearly pure water vapor in the atmosphere. An estimated 80,000 cubic miles of water or 88 quadrillion gallons of water evaporates from the oceans each year. Around 3,000 cubic miles of water vapor is in the atmosphere at any one time.

If all this water vapor were too precipitate at once, the Earth would be covered in one inch of rain. Unfortunately, over the last few years, the storm track has remained mostly north of the Central Coast, preventing us from receiving normal amounts of rain from all this water vapor.

When the weather doesn’t cooperate, could an abundant supply of fresh water be directly harvested from the sea?

People have removed salts from seawater using solar stills for thousands of years. Today, the United States Navy produces fresh water for its crews by using both evaporators and filters.

When I was stationed on the USS McCandless, a Knox-Class Frigate in the 1980s, we were always running low on water. On most nights, our trusty Kaman SH-2 Seasprite helicopter would get a bath of fresh water at the end of the day, while the ship’s crew would not. When we had enough fresh water, personal showers were limited to about two minutes. In other words, no Hollywood showers were allowed. On today’s modern Navy vessels, fresh water is much more abundant.

Producing fresh water from the ocean is a growing trend throughout the world, including California. John Steinbeck of Tenera Environmental Services in San Luis Obispo told me that his company is currently conducting several marine biological studies for proposed desalination plants in the state.

Large-scale desalination plants move seawater at considerable pressure through a semi-permeable membrane. The smaller water molecules pass through the membrane, while the larger salt molecules are trapped behind in a process called reverse osmosis. This process is energy intensive and many current or proposed desalination plants are located near existing power plants.

They are also high-maintenance undertakings with quite a few working parts and membranes that can foul with debris and tiny marine organisms such as red tide.

Despite these obstacles, the largest desalination plant in the Western Hemisphere is currently under construction in Carlsbad, Calif. after gaining approvals from the California Coastal Commission, State Lands Commission, Regional Water Quality Control Board and other regulatory agencies.

It’s estimated that when it comes online in 2016, the plant will be able to produce 50 million gallons of drinking water every day.

Along the Central Coast, the Diablo Canyon Power Plant’s small desalination plant produces around 500,000 gallons of fresh water per day for its 1,500 employees, plant operations and safety-related systems.

Other small desalination plants along the California coast that are active include municipal plants in Sand City and Santa Catalina Island, as well as facilities serving the Monterey Bay Aquarium, the Navy base on San Nicholas Island and Chevron Gaviota oil/gas.

The city of Morro Bay has a desalination plant, which was built to desalinate seawater but now mostly treats brackish groundwater on an intermittent basis.