The What’s Up with Science? blog series offers a deep dive into science, technology, and innovation topics on the minds of the public. The series matches technical explanations with relatable analogies to explain opportunities and answer the ultimate question: Why should we care?
At one point in my life, I swore I would audition for Survivor, the television show that dares tribes of contestants to live without resources on a deserted island (while voting each other off the show one by one, of course). I envisioned using my scientific knowledge to remove salt from buckets and buckets of plentiful ocean water, providing an unlimited drinking supply for my tribe. I’d be a hero and win the title of “sole survivor.” Hey, a girl can dream.
That dream was crushed a few years ago when I learned that Survivor contestants get their water from a well that is built and filled by the production crew. I suppose this makes sense since humans can’t drink saltwater, but on a show purportedly about survival, I’d rather see contestants try their hands at desalination.
Desalination is the removal of salts and other minerals from water. The process is inspired by nature’s hydrologic cycle, the same cycle experienced by Survivor contestants when water evaporates from the ocean, collects in the clouds, and then falls from the sky as freshwater (i.e., rain). Most desalination techniques can be boiled down (pun intended) to heat- or membrane-based methods, though other methods—including those based on catalysis—also exist or are in development.
Heat-based desalination is accomplished using distillation, which directly mirrors the hydrologic cycle. Saltwater is boiled to form water vapor, leaving the salts behind, and the vapor is recondensed into pure, liquid water elsewhere. The heat needed to boil the water can be generated by electricity or sourced from waste heat streams. The sun’s heat can also do the job and would be my personal choice for seawater desalination on the Survivor shore.
Alternatively, membrane-based desalination methods typically utilize a process called reverse osmosis. Saltwater is pushed through a porous material called a membrane. The membrane’s pores are so small that they only allow water to pass through, trapping salts and minerals on the opposite side. While not ideal for Survivor contestants, who aren’t allowed to bring membranes (or anything, really) with them onto the show, reverse osmosis is commonly used to desalinate seawater in real life.
You may be wondering at this point why desalination isn’t more common, since it would seemingly provide an unlimited supply of potable water. The primary reason is a large energy requirement, which often makes the process expensive. The amount of energy needed to perform desalination depends on the technique used (i.e., reverse osmosis demands less energy than distillation) as well as the concentration and types of contaminants in the water. Even so, in some locations without access to sufficient freshwater, desalination may require the same amount of energy as transporting freshwater over long distances.
Another challenge is disposing of brine, a highly concentrated salt solution and the byproduct of desalination. Fortunately, many methods for environmentally safe disposal have been developed. As just one example, brine can be treated to remove any contaminants and then diluted with other wastewater streams destined for the ocean.
As freshwater sources become scarcer in many parts of the world, desalination has become a real option to provide water for human consumption and agriculture. Desalination is already used throughout the United States, in more than 120 countries, and even on the open seas (where ships implement the technique to generate their own drinking water). Industries requiring highly purified water, like pharmaceutical, semiconductor, and disk drive manufacturing, also benefit from desalination. Maybe one day it’ll even be a storyline on Survivor.
The utility of desalination for applications ranging from water security to advanced manufacturing to humanitarian aid has not gone unnoticed by the U.S. Government. At the State Department, for instance, public-private partnerships accelerate the entry of sustainability solutions, including desalination, into the market. From various corners of the federal government, disaster relief, innovation challenges, and water infrastructure projects at home and abroad have all incorporated desalination, and more applications are sure to come.
You don’t need to pretend to survive on a deserted island to experience the benefits of desalination. Where did your drinking water come from today?
About the Author: Aubrey R. Paris, Ph.D., is a Science and Technology Policy Adviser in the Office of the Science and Technology Adviser to the U.S. Secretary of State (STAS) at the U.S. Department of State. She received her Ph.D. in Chemistry and Materials Science from Princeton University and B.S. in Chemistry and Biology from Ursinus College.