How to Purify Water Using the Sun and a Water Bottle

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Written by Bernie Carr

Last week, I posted an article about how sunlight can help you survive. Today, we will look at details on how it can help you disinfect water in an emergency if you don’t have a water purifier.

Purifying water using the sun’s rays is also known as SODIS “solar disinfection.” SODIS is likely the most inexpensive way to disinfect water. The method is used in many developing countries. Originally devised in the 1980s, it was used to inexpensively disinfect water for oral rehydrating solutions, according to the Centers for Disease Control (CDC). Today, around two million people (in 28 countries) use solar disinfection on a daily basis.

How it’s done

All you need is a plastic water or soda bottle – these are PET bottles, which can be identified by “recycling number 1” under the bottle. It should be in good condition.

If the water you will be purifying is too murky, you’ll need to filter it first. Use a bandanna, coffee filter, paper towel or even a clean t-shirt to filter out any soil and other solids from the water.

Fill the bottle with clear water.

Shake the bottle well.

Set the filled bottle out in the sun for six hours on a sunny day. If it cloudy, then you need to leave it out for two days.

How does it work?

SODIS works via:

  • UV rays destroy the cell structures of bacteria.
  • The rays of the sun heat the water – as the water temperature reaches 122 Fahrenheit, the disinfection process accelerates.
  • UV light combined with oxygen in the water produce oxygen free radicals and hydrogen peroxides that can also damage germs.


Solar disinfection kills viruses, bacteria, and parasites such as giardia and cryptosporidia in the water. Therefore, it reduces the likelihood of getting diarrhea from drinking the water.

PET soda bottles are commonly available and can be found almost everywhere. If you take a walk along the beach, the desert or the mountains – anywhere you go, you will find plastic water bottles. As long as the bottle is a PET bottle, and in good condition, you can use it. There is virtually no cost if you are reusing recycled bottles.

The method is very simple and easy to teach to someone.

Soda disinfection also causes very little change in the taste of water.


Solar disinfection kills germs but does not get rid of metals or chemical pollutants.

You need to filter the water first, as it has to be clear water for the method to work.

You can only purify with as many bottles as you have therefore there is no large scale way to do it. The maximum size bottle you can use is a 2-liter bottle.

The method also takes some time to work especially on cloudy days: leave out the bottle for six hours on sunny days, or two days on cloudy days.

There is some concerns about chemicals in plastic leaching into the water, however, studies by a research group in Eawag, the Swiss Federal Institute of Aquatic Science and Technology, have shown that solar disinfection does not pose a health risk.

In conclusion

Of course, ideally you would have a water purifier with you – I rely on Berkey for home use and the Survivor Filter Pro X for camping. I also recommend storing water in your car.

But if you are ever stuck in your apartment and tap water is no longer safe, or stranded somewhere with no water purifier with you, don’t forget that sunlight and a PET plastic water bottle can help you disinfect water. Find a water source (no toxic runoff – as best as you can tell). Filter the water with whatever you have – bandanna or t-shirt, cover and shake the bottle. Leave the bottle out in the sun for six hours if it’s sunny (or two days if it’s cloudy) and you have purified water.

If you are interested in the research behind this method, a great resource is the SODIS site.

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About the author:

Bernie Carr is the founder of Apartment Prepper. She has written several books including the best-selling Prepper’s Pocket Guide, Jake and Miller’s Big Adventure, The Penny-Pinching Prepper and How to Prepare for Most Emergencies on a $50 a Month Budget. Her work appears in sites such as the Allstate Blog and, as well as print magazines such as Backwoods Survival Guide and Prepper Survival Guide. She has been featured in national publications such as Fox Business and Popular Mechanics. Learn more about Bernie here.

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