How to Desalinate Water
July 11, 2014 | 6 comment(s)
Water is a dynamic resource. It depends on the season, the location, the temperature, and a host of other factors. But one thing you can always count on is that at any given time about 97% of the world’s water is tied up in the ocean. The other 3% is found in streams, lakes, groundwater, and ice. Looking at the numbers, it’s obvious that tapping into the ocean’s reserves opens a world of possibilities, especially when it comes to an emergency.
Using ocean water in an emergency is an obvious possibility for people living in coastal or island areas. When one considers the number of vacation destinations in these areas, the application becomes much wider. Natural disasters, especially, have the ability to interrupt or cripple fresh water supplies in these areas.
However, people cannot safely drink ocean water. The reason for this lies in the kidneys. As the kidneys process salt, they are only capable of producing urine that is less salty than ocean water. This means it requires more water than that which is available in ocean water to rid the body of excess salt. So as a person drinks ocean water they become increasingly dehydrated, rather than rehydrated. This makes desalinating ocean water an appealing option.
If removing salt from ocean water is part of your emergency preparedness plan, it will generally take a bit more effort and/or equipment than other water purification processes. Describing the desalination process at some length emphasizes the fact that the key word here is preparedness. For desalination to be useable at home, some foresight will go a long way.
Desalination: How does it Work?
Desalination or Desalting is the process of removing salt from ocean water to produce fresh water. Desalinated water can be used for drinking water, or for agriculture, or industrial use.
Desalination is an inherently energy intensive process. There is a reason why wells are drilled, treatment plants are used, and conservation efforts are exhausted before agencies, governments, and authorities consider using desalination. That reason is money. In many cases ocean water must be treated and/or filtered before the desalination process can take place. This means that aside from consuming a great deal of energy, it also requires equipment, facilities, and manpower. Ultimately, this results in expensive water.
Despite the cost, removing salt from ocean water is still a useful process that is in use in many areas. Expensive water is much better than no water, and as technology advances, renewable energy sources such as wind or solar power make desalination more viable and affordable.
Types of Desalination
There are different ways that this process can take place. The two most common are distillation and reverse osmosis.
- Distillation is the process of boiling ocean water and collecting the condensate which has left salt and other minerals behind.
- Reverse osmosis uses pressure and a semi-permeable membrane to accomplish the same thing. Osmosis is a naturally occurring process in which a solvent (water) and a solution (salt water) equalize across a semi-permeable membrane. This occurs as the solvent flows from less concentrated to more concentrated water until equilibrium is achieved. Reverse osmosis, as the name implies, pushes the process the other way. Pressure is applied to the salt water side pushing water molecules to the less concentrated side producing clean, salt-free water.
Ways to Desalinate Water in an Emergency
There are several different techniques you can use to desalinate water during an emergency.
- Home distillation is a possibility. It requires a lot of fuel, however. In an extended emergency this could become a problem. Fuels (propane, etc.) may not last and wood collection could become too labor intensive to be worthwhile.
- Solar distillation may be used as well, but production from a solar still is generally small. If solar power is going to be used, preparedness will be the key. It would be a great idea to invest in something like a solar oven to make the process more efficient.
- Reverse osmosis is a viable option in an emergency as well. It will, however, require some investment and planning.
- Purchase a Desalinator. For someone who lives in an area where using salt water in an emergency is their best option, there are some good products out there. There are a couple common types.
- Powered Desalinators: Battery or generator operated. Powered desalinators are capable of supplying a decent volume of water, but they will require ongoing maintenance of batteries, solar panels, or generators to be sure everything will function in an emergency. They’re also relatively expensive. A common model is the Katadyn PowerSurvivor 40E. It retails for around $4000.00. It runs on 12 volts and puts out 1.5 gallons per hour. There are other models as well, but this one is fairly typical of price and output. They go up or down in price based on options.
- Manual Deslinators: The Katadyn Survivor 06 is a good example of a manual desalinator. They are generally operated by pumping to supply pressure to force water through the membrane. These again highlight the large amount of energy needed for desalination. The Katadyn Survivor requires 40 pumps per minute to produce 0.89 liters per hour. That is 2400 pumps for less than one liter of water! In an emergency you’ll be glad to have the water, but a small manual desalinator will only provide enough water for one or two people and it will take a lot of work to get it.
There are many scenarios where desalination may be your best option for an emergency water supply. If this is the case, it’s critical that you do some planning. You may need to learn specific techniques and decide how to best accomplish the task. In some cases it requires a significant amount of equipment. More so than with almost any other emergency water supply plan, desalination requires planning and forethought in order to be prepared.
Is a desalinator not in your price range for emergency supplies? For a step-by-step tutorial on how to distill your own water at home, check back for our upcoming article on home distillation.
Author Bio: Joe Huish has worked for the Central Utah Water Conservancy District’s drinking water treatment sector for 10 years. He studied Geology at Utah State University where he earned a bachelor’s degree. He’s an avid outdoorsman and is a bit of a gear nut. He enjoys fishing, hunting, jeeping, and camping.