Solar Water Purification
Simple, Cheap and Effective
by Nancy Hearn

Solar water disinfection in Indonesia

Solar water purification is a method of water disinfection that everyone should know about for emergency, natural disaster or wilderness survival situations. It is simple, effective, and cheap.

This method of water disinfection effectively rids the water of disease-causing biological substances such as bacteria, viruses, and protozoa.

The main disadvantage of this method is that it does not remove non-biological substances such as heavy metals and toxic chemicals.  

There are 3 main types of solar disinfection, which use electricity, heat, or ultraviolet radiation.

1. The electric form of solar water purification uses electricity generated by solar panels to disinfect water.
2. Solar thermal disinfection uses solar heat collectors to increase water temperature to 70 to 100 degrees C., which destroys many dangerous biological agents.
3. Solar ultraviolet disinfection of water uses only sunlight and plastic bottles.

Solar Water Disinfection (SODIS)

The ultraviolet form of purification is most widely used throughout the world and is called Solar Water Disinfection, or SODIS for short.  

This simple and effective method can be used by anyone and is also recommended by the World Health Organization as a method of household water treatment and storage.

Benefits of Solar Water Purification

Simply exposing contaminated water to the sun’s rays has many benefits.  Just a few of the known benefits include:

1. The sun’s UVA rays destroys cell structures of pathogens
2. UVA rays activate the oxygen in water, forming oxygen free radicals and hydrogen peroxides, which kill pathogens
3. The cumulative effect of exposing water to solar energy heats the water and will speed the disinfection process.
4. The method is simple, portable and inexpensive, requiring only sunlight and plastic bottles.

Instructions for Using SODIS

The process for household application is simple and requires minimal cost.

1. Acquire plastic bottles.  For effective disinfection, use clear, colorless PET bottles that are free of surface scratches. Remove any labels and thoroughly wash the bottles before use.  PET bottles will have a number 1 on the bottom of the bottle.  Note:  Some glass and polycarbonate bottles (the heavier plastic) block UVA rays and cannot be used. 
2. Fill bottles with water.  Fill a bottle with source water about ¾ full and then shake it up for half a minute or so to activate the oxygen. Then fill the rest of the bottle and seal it with the cap.
3. Expose bottles to sunlight.  Lay the bottles down on their sides to get full exposure to the sun. The length of time depends on the amount of sun exposure.  General recommendations for duration:  sunny (no more than 50% cloud cover) = 6 hours;  cloudy (with little or no rain) = 2 days; and rainy (continuous) = not effective for disinfection.
4. Drinking or storing the water.  After the recommended length of sun exposure, you can either drink the water directly from the bottles or pour into a glass or cup.  Or you can store the water for a few days.

Cautions and Limitations

1. When the source water is very cloudy (turbid), solar water disinfection cannot be used alone.  You would need to run the water through a sediment-type filter before using solar disinfection.
2. Be sure to use the full length of sunlight exposure that is recommended.  Inadequate sun exposure may not completely disinfect the water.
3. We would not recommend storing the solar disinfected water for more than a few days. Some believe it is possible for pathogens to re-grow in the bottles when removed from sunlight.
4. We are also concerned about the leaching of plastic materials into the water, even though some studies have shown that the levels of plastic compounds (such as phthalates and adipates) from PET bottles during solar exposure were far below the World Health Organization guidelines for drinking water. However, according to Medicinenet.com, recent studies have shown that “reusing bottles made of PET can, in fact, be dangerous. PET was found to break down over time and leach into the beverage when the bottles were reused.” However, we have found at least one company, Puralytics, that uses BPA free plastic for a solar bag (see ad below). As of this writing, we are not sure if BPA-free bottles can be used in place of PET bottles. We will update this page when we find out. 
5. We have found at least one company that uses 
6. Solar water purification does not remove toxic chemical and heavy metals in water.

Editor's Comments

Even though I love the concept of solar water purification and would certainly use the method in an emergency or survival situation, I would not want to rely on it for daily water because of the issues referenced above regarding the plastic bottles.  

We do not want to contribute to environmental plastic pollution and we believe most plastic bottles leach unhealthy contaminants into water (especially when exposed to heat and light).

For limited use, we like the Puralytics Solar Bag Water Purifier. It is lightweight, portable, and the plastic is BPA-free!  So far, we are impressed and reviews are excellent.

Reference

Medicinenet.com; What is polyethylene terephthalate (PET, PETE); 2014.

Further reading . . .

Safe Water Bottles: Check to See That They Are BPA-Free   

Return from Solar Water Purification to Filtered Drinking Water