How To Remove Salt From Water Naturally

Why don't nosotros get our drinking water from the ocean past taking the salt out of seawater?

Peter Gleick, president of the Pacific Institute, distills an answer:

Why don't we get our drinking water from the ocean by taking the salt out of seawater? — Credit: Getty Images

Even with all of the h2o in Earth's oceans, we satisfy less than half a percent of human h2o needs with desalinated water.* We currently utilise on the order of 960 cubic miles (4,000 cubic kilometers) of freshwater a yr, and overall in that location's enough water to go around. There is increasing regional scarcity, though.

So why don't we desalinate more to alleviate shortages and growing water conflicts?

The problem is that the desalination of water requires a lot of energy. Salt dissolves very easily in h2o, forming strong chemical bonds, and those bonds are difficult to intermission. Energy and the technology to desalinate water are both expensive, and this means that desalinating water can be pretty costly.

It's hard to put an exact dollar figure on desalination—this number varies wildly from place to place, based on labor and energy costs, land prices, financial agreements, and even the salt content of the water. It can cost from just nether $ane to well over $two to produce one cubic meter (264 gallons) of desalted water from the ocean. That's virtually every bit much as 2 people in the U.South. typically become through in a day at habitation.

Just switch the source to a river or an aquifer, and the cost of a cubic meter of water can collapse to 10 to xx cents, and farmers oftentimes pay far less.

That means it's still almost ever cheaper to use local freshwater than to desalinate seawater. This price gap, nevertheless, is endmost. For example, meeting growing demand by finding a new source of water or by building a new dam in a place like California could cost up to 60 cents per cubic meter of water.

And sometimes these traditional ways of "harvesting" h2o are no longer available. Every bit such, this cost effigy is expected to keep to ascent, which is why California is now seriously considering desalination and why the urban center of Tampa, Fla., decided to build the biggest desalination constitute in the U.S.

The International Desalination Association says that every bit of 2007 in that location were well-nigh xiii,000 desalination plants operating effectually the world. They pumped out approximately 14.7 billion gallons (55.6 billion liters) of beverage freshwater a 24-hour interval. A lot of these plants are in countries like Kingdom of saudi arabia, where energy from oil is inexpensive but water is deficient.

So how is energy used to dissever common salt from h2o?

At that place are two basic methods for breaking the bonds in saltwater: thermal distillation and membrane separation. Thermal distillation involves rut: Boiling water turns it into vapor—leaving the salt backside—that is collected and condensed dorsum into water by cooling it down.

The most mutual type of membrane separation is called reverse osmosis. Seawater is forced through a semipermeable membrane that separates table salt from water. Because the technology typically requires less energy than thermal distillation, virtually new plants, like Tampa'southward, now apply contrary osmosis.

There are ecology costs of desalination, as well. Bounding main life can get sucked into desalination plants, killing small sea creatures like baby fish and plankton, upsetting the food concatenation. Also, there's the problem of what to practice with the separated table salt, which is left over every bit a very full-bodied alkali. Pumping this supersalty water back into the sea can harm local aquatic life. Reducing these impacts is possible, only it adds to the costs.

Despite the economical and environmental hurdles, desalination is becoming increasingly attractive as we run out of water from other sources. Nosotros are overpumping groundwater, we have already built more dams than we can afford economically and environmentally, and we take tapped about all of the accessible rivers.

Far more must be done to use our existing water more efficiently, only with the world'south population escalating and the water supply dwindling, the economic tide may soon turn in favor of desalination.

The Pacific Plant is an Oakland, Calif.–based, nonprofit think tank devoted to solving the world's water needs. The organization reviewed these bug in depth in a 2006 written report entitled "Desalination, with a Grain of Common salt." Peter Gleick also authored a book in 2000 chosen The World's Water, in which he and his colleagues explore desalination and other topics.

*Description (8/24/08): This sentence has been modified since the original posting.