According to the U.S. Geological Survey, the Earth contains about 366 quintillion gallons of water, of which about 97.5 percent is salt water. Unfortunately, humans can only easily access less than 0.007 percent of Earth’s water.
From this data, it appears that desalination—creating freshwater by filtering out the salt and minerals from ocean water—may be the magic bullet to solve the global water crisis.
This month, a plant in Carlsbad, Calif., headed by Poseidon Resources, is negotiating a 30-year water purchase agreement that would require the San Diego County Water Authority to purchase 48,000 acre feet (roughly 15.6 billion gallons) of desalinated water per year. Poseidon needs this agreement to seize funding for a $900 million construction project.
With desalination, however, there is more than meets the eye. Currently, desalination is not economically or environmentally viable for commercial use. Therefore, people must be wary of the downsides of desalination before blindly letting Poseidon sign this agreement.
Production costs vary among desalination methods, and shipping the resulting water throughout a country like the U.S. provides additional costs. Additionally, constructing these plants is fairly costly; the Santa Cruz Water Department is fighting to build a $123 million plant in Monterey Bay, while Poseidon’s Carlsbad plant will cost a whopping $900 million.
Additionally, the various desalination methods have their own shares of problems. The filtration process Poseidon uses, reverse osmosis, applies pressure to “push” water through semipermeable membranes, leaving the various solutes behind. Reverse osmosis, unfortunately, is not 100 percent efficient (about 10 to 25 percent of the input volume is discharged as wastewater), requires seawater pretreatment and large sums of energy (most of which is derived from fossil fuels) and produces toxic waste in the form of used membranes.
Other methods do not fare much better. The most common desalination method, multiple-stage flash distillation (MSF), involves repeated vaporization to carry the pure water away from its impurities. MSF requires huge thermal energy inputs in order to vaporize water at an industrial scale. On the other hand, although solar desalination does not rely on fossil fuels for energy, it requires high amounts of solar energy and thus may be unviable in certain regions.
As always, conservation may be more beneficial than desalination or other water production methods; curing a disease costs much more than preventing it in the first place. Simple things, like taking shorter showers or turning off an unneeded faucet, can go a long way. If, however, desalination is going to solve our water woes, then the various processes must be refined to minimize costs and pollution.
At a glance, environmental buzzwords like “desalination” may seem magical, but one must look below the surface before deciding what is best for the economy and the planet.