Thursday, August 30, 2012

DIY Survival Gear - How to Make a Portable SODIS Device

Portable SODIS Device

When it comes down to your survival, sometimes you not only have to think outside the box but you may need to use the box itself. There are many critical situations you may find yourself in during a crisis or an emergency. There is one that ranks higher up the list than others. This is the need for safe drinking water. No matter where you are or what your circumstances you will always need a safe and clean source of water for drinking. Unfortunately, you may not always have the ability or means to purify a source of water for drinking. Here is a simple gear set-up that gives you an alternate means to disinfect your water that doesn’t involve chemicals or fire and can make it relatively safe to consume.

SODIS is the disinfection (**edit) of water by using the power of the sun. There is a simple SODIS device that can be easily made, carried in your backpack, requires a minimum of space and weighs next to nothing.

Here’s what you will need to make a simple SODIS device for disinfecting water in an emergency.

First we need to think “flat”. This usually amounts to less room and less weight when it comes to gear. The traditional SODIS method usually involves a round plastic bottle. So to save space because round takes up more room we will use a bag instead. A large bag can be folded and stored flat and will take up a lot less room. For this project and for the sake of simplicity, we will use a plastic freezer bag. This is an everyday item that everyone generally keeps handy in the kitchen.

While still thinking “flat”, the next item you will need is a dark-colored bandanna or a piece of black cloth or material. This dark cloth needs to be at least as large as the plastic bag you will be using.

The third item you will need is a piece of cardboard from a box that is just slightly smaller than your bag. This will make storing the pieces of your SODIS device easier. This cardboard will be used to help us make a solar reflector.

The last item you will need is a sheet of heavy duty tin foil. This needs to be large enough to cover the entire piece of cardboard. This will be our solar reflector.

Bag Filled with Water

To use the device simply put your filtered water in the bag (you can also use the bandanna to filter your water). Fill the bag approximately half full of water and then work to eliminate as much air as possible out of the bag. When laid flat, the bag with the water should be about the thickness of your hand. By doing this there will be better penetration of the sun’s UV rays. Make sure to lay your bag in a bright sun-lit area for at least six hours. It also helps to place your bag of water on a dark surface such as a bandanna or piece of cloth. This will aid in heating the water. It can be folded when not in use and kept inside the bag. It can then be easily stored in the bottom of your pack, under the seat of your vehicle or you could even make a smaller version that could fit in your pocket. If you don’t have plenty of sunlight, it may require an additional day to treat the water. If it looks like it might rain, you may want to keep a bucket handy to catch some rainwater. 

You might also want to include an extra bag as a container to retrieve water in or if your original bag develops a hole. Otherwise, you're going to need some duct tape to patch the hole.

Special Notes:

1. SODIS is not as reliable as distillation, boiling or chlorination for treating drinking water.

2. Using the SODIS method is better than drinking untreated water.

3. The SODIS method can be relied on to inactivate bacteria only on sunny days.

4. The water being treated must be adequately filtered before treatment to reduce turbidity.

5. Solar disinfection of drinking water should not be your primary means of treating water for consumption.

One of the best parts of this DIY survival gear is that it can be readily made from simple household items that can be found in almost everyone’s home.

Got portable SODIS?

Staying above the water line!


Note from RW: Post was edited to correct terminology. Thank you.


Anonymous said...

I like it. Water is a necessity and finding ways to purify it in the field is good knowledge. Thanks for posting this.

riverwalker said...

To: anonymous 7:12

Using a bag gives you more surface area that is exposed to the sunlight. The depth of penetration for the sun's UV rays is also less.

If you don't have a dark cloth, you could use most any dark surface to place it on while it's exposed to the sunlight to help absorb additional heat from the sun.

Thanks anon.


Anonymous said...

Is agitation of container a factor in how well this method works ? I have wondered if the person is forced through some circumstance of having to continue to move, if the water sloshing around the container does not get pastuerized and cleansed. I have not found a definitive answer to this.

Anonymous said...

You can use a soda straw or plastic tube to suck most of the air out of the bag. The straw/tube can also be stored with the bag.

riverwalker said...

To: anonymous 12:27

I don't really know how it would affect the water in the bag as long as it was kept flat to minimize the depth the sun's rays have to penetrate.

I do know that if you are using a bottle that it is necessary to rotate the the overall exposure of the water in a bottle to UV rays is greater.

If you use any larger type bottles (3 liter), the process doesn't work as well.

The bag in the picture is a gallon size and was slightly more than half full...which is not bad for one person. If you had more persons in your group, you need additional SODIS devices set up.

In my area, we get 12 hours of good sunlight most everyday in the summer. This makes it possible to treat a gallon a day with a small set up as I described.

Thanks anon.


riverwalker said...

To: anonymous 2:18

Great tip anon!

Now I need to add one of those little coffee stirrers to the kit to help in removing as much air as possible.

Thanks anon.


Anonymous said...

Just want to say, that while your design is actually pretty decent, the reasoning behind some of your choices is flawed.

Heat has absolutely nothing to do with the functionality of the SODIS method.

That aside, by blind luck, your design is actually fairly reasonable. You want to avoid punctures, and it helps. You absolutely MUST filter out particulates, and you mention that...if just barely. And the Reflector increases the amount of UV light hitting the plastic bag, thus increasing effectiveness by a slight amount.

Still, you should really take this down, research what SODIS actually is, and re-write the article in a way that covers actual information about the system.

UV radiation alone destroys the bacteria and viruses within six hours. Parasites require more than six hours, though giardia is neutralized in the time period, cryptosporidia needs at least ten hours. And if you live in an area where Amoebas are an issue, you need to have the water at 50c for an hour, something you are not likely to obtain with this method unless you have very, very bright sunny days. And the plastic bags wouldn't survive it, in any case.

riverwalker said...

To; anonymous 4:23

I stand corrected in that it is the UV rays that disinfect the water. In order to Pasteurize the water it would have to get to a temp of 160 degrees Fahrenheit...and like you mentioned that probably wouldn't happen.

Tried the bottle method but scratches eventually make the bottles work inadequately and no rotation of the bag is required.

Still looking for a better and easier way to treat water...just have to put my thinking cap back on.

Thanks for the additional input.


Josh said...

Interesting setup. In addition to the comment about the incorrectness of calling it pasteurization, etc., I guess the first thing I noticed when reading the article was the use of the term “water purification.” What SODIS does is disinfect the water – it kills pathogens in it, but doesn’t remove anything as real water purification would do. Get it – SOlar DISinfection. True water purification would require the removal of any harmful chemicals and dissolved substances in the water. Knowing that you can kill pathogens in water by letting it sit in the sun is definitely handy knowledge to have, but you could conceivably still be drinking water that is poisoning you because of harmful chemicals in it.

Not that the article and the idea isn’t good, but maybe a little flawed in its execution.

riverwalker said...

To: Josh

While there may have been errors in my semantics, the point I was trying to get across is that there are other ways besides boiling, distillation and chemical treatments that can be used to make water safe to drink.

Thanks Josh.


Anonymous said...

One of the ways to use the sun to disinfect water is to use a small soy candle in a bag next to the water bag. When the candle melts, the water has reached pasteurization temperatures. This type of system is used in the desert with a wax insert in the water bag which melts at the correct temperature.

riverwalker said...

To: anonymous 12:27

Great tip!

Thanks anon.


Unknown said...

Nice idea, thanks for sharing that info

Jordan said...

I think this is a great idea. I have read most of the comments, and they are quick to fault the system, although if you have no fresh water, and these are the only supplies you have, this would certainly be better than drinking raw water. Great post!

riverwalker said...

To: Max

Thanks Max.


riverwalker said...

To: Jordan

While it is not as good as a reverse osmosis system, it's a lot easier to put together from simple household items.

The treatment of water by this method if no other method is available may enable you to avoid a bad case of dysentery or diarrhea...which could make you even further dehydrated.

Thanks Jordan.


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