The short answer is YES! At its most basic, solar disinfection (SODIS), requires a PET plastic bottle, some water that needs to be disinfected, and sunlight. Of course, this method has pros and cons so keep reading for the details.

Intro

Whether or not you consider yourself a prepper, you may find yourself in a survival situation and in need of clean drinking water. Solar disinfection (SODIS) is one method that may prove essential. It’s cheap, proven effective, and has been used worldwide.

History

Ancient civilizations in Asia used sunlight to treat drinking water. More recently, in the 1980s researchers confirmed that this can be an effective method of purifying water. In the early 2000s, The Swiss Federal Institute of Aquatic Science and Technology (EAWAG) made this technique accessible to developing countries around the world, especially to poor rural populations, as a safe and effective means of creating safe drinking water.

What SODIS does

Solar disinfection kills or deactivates pathogens in the water. Bacteria, viruses, and protozoa may be harmful to humans and often cause stomach cramps and diarrhea. Some common waterborne pathogens are cryptosporidium, E. coli, cholera, and giardia.

What SODIS does not do

SODIS does not remove chemicals or heavy metals from water. This includes things like fluoride, chlorine, lead, and mercury. SODIS also does not remove suspended particles (turbidity) or sediment. In fact, high turbidity renders solar disinfection ineffective. 

How SODIS works

SODIS uses ultraviolet (UV) light and solar heat to destroy or inactivate water-borne microorganisms. UV light, capable of burning human skin, can also destroy or inactivate single-cell organisms, like water-borne microbes. UV light also causes dissolved oxygen in the water to become reactive, which further damages the microbes. 

And if the UV light alone isn’t enough to destroy the biological contaminants in the water, it is enhanced by the increase in temperature. The water will not get hot enough to boil, but it will become pasteurized. This just means that it is heated to less than boiling temperature. When boiling water for disinfection, water must be boiled for at least 3 minutes. Even though SODIS isn’t heating water to a boiling point, it is heated for a much longer time, which contributes to the disinfection. 

SODIS is effective in all air temperatures, as long as there is sunlight. 

What you need

• Clear containers made of PET plastic with lids

PET plastic bottles can be identified by the recycle symbol with a 1(♳). They are lightweight, shatterproof, and contain no BPA that can leach into the water. Bottles must be a maximum of 2 liters in size and made of clear, not colored plastic. Volumes of water larger than 2 liters may not get enough UV light exposure. Colored plastic can block UV light. Plastic that is excessively scratched can’t be used for the same reason. Labels must be removed to allow for maximum sunlight exposure. It is better to have multiple bottles as the process does take several hours. 

You may use glass containers, such as mason jars if that is what you have on hand. Again, the glass must be clear and the labels removed. Be aware that some types of glass may contain coatings or laminations that inhibit UV light. Also, glass will be heavier than plastic and can potentially break.

• Water that needs to be disinfected

Use the clearest water you can get. If the water is more than minimally turbid (cloudy), it must be filtered first even if just crudely using some fabric. This is crucial because UV light can’t penetrate cloudy water. If you’re unsure about the clarity of the water, remove the lid, place the bottle full of water on top of some newsprint, and look down at the print through the opening of the bottle. If you can read the print, the water is clear enough. 

• Sunlight

Sunny days require the shortest exposure times for SODIS to be effective, but even on a cloudy day UV light is present. SODIS is not effective, however, during days of continuous rain. 

How to use SODIS

• Fill your container about ⅔ full with water
• Place the lid on it and shake for about 20 seconds to oxygenate it well
• Fill the container the rest of the way and recap it
• Place the container horizontally or at an angle facing the sun
• Wait 6 to 8 hours on a sunny day or 48 or more hours on a cloudy day
• Drink up!

Tips for improving SODIS

• Place your water bottle on a reflective surface, like a piece of aluminum or corrugated steel. This maximizes the light and heat available.
• Paint 1 side of the bottle black and face the clear side toward the sun. This allows light to penetrate through the clear side while the black side absorbs the heat.
• If you have any citrus, squeeze a few drops of juice in the water. A natural chemical (psoralen) in the citrus reacts when exposed to UV light and helps speed the process of disinfection.
• Add a dash of table salt. Iodized salt (table salt) will react with some types of clay in the soil. If this is causing the cloudiness in the water, the salt will cause the particles to clump together and settle, making it easier to remove or filter out.

Concerns of plastic

Some people have a legitimate concern about toxic chemicals leaching from plastic bottles into the water, especially since the bottles are exposed to the sun and heat. EAWAG has tested for DEHA and DEHP and found the levels to be far below levels of concern. Water disinfected using SODIS isn’t usually stored in the bottles long term, so there is less concern about leaching toxic chemicals. PET plastic is fortunately a safer plastic option.

Pros and Cons of SODIS

Pros

• It’s cheap – you need minimal, inexpensive supplies 
• It’s effective – it has been tried and tested and, if done correctly, greatly improves the quality of water contaminated with bacteria, viruses, and protozoa
• It does not change the taste of the water

Cons

• Even on a good day, it can take several hours
• You can only treat as much water as you have bottles to hold
• Other methods, such as chlorination and boiling, are more effective if you have the option to use them. 

Conclusion

Solar disinfection may not be the best option for every situation, but it is a great technique to know. You may not always have the equipment or supplies to chlorinate or boil water in an emergency, but if you know how SODIS works you can still be prepared.